| Message ID | 20220429000947.2172219-2-jiaqiyan@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Memory poison recovery in khugepaged collapsing | expand |
On Thu, Apr 28, 2022 at 5:09 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > Make __collapse_huge_page_copy return whether > collapsing/copying anonymous pages succeeded, > and make collapse_huge_page handle the return status. > > Break existing PTE scan loop into two for-loops. > The first loop copies source pages into target huge page, > and can fail gracefully when running into memory errors in > source pages. Roll back the page table and page states > in the 2nd loop when copying failed: > 1) re-establish the PTEs-to-PMD connection. > 2) release pages back to their LRU list. Could you please include a changelog next time? It is really helpful for reviewers. > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > --- > include/linux/highmem.h | 19 ++++++ > mm/khugepaged.c | 138 ++++++++++++++++++++++++++++++---------- > 2 files changed, 124 insertions(+), 33 deletions(-) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index 39bb9b47fa9cd..0ccb1e92c4b06 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from) > > #endif > > +/* > + * Machine check exception handled version of copy_highpage. > + * Return true if copying page content failed; otherwise false. > + * Note handling #MC requires arch opt-in. > + */ > +static inline bool copy_highpage_mc(struct page *to, struct page *from) > +{ > + char *vfrom, *vto; > + unsigned long ret; > + > + vfrom = kmap_local_page(from); > + vto = kmap_local_page(to); > + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE); > + kunmap_local(vto); > + kunmap_local(vfrom); > + > + return ret > 0; > +} > + > static inline void memcpy_page(struct page *dst_page, size_t dst_off, > struct page *src_page, size_t src_off, > size_t len) > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 131492fd1148b..8e69a0640e551 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -52,6 +52,7 @@ enum scan_result { > SCAN_CGROUP_CHARGE_FAIL, > SCAN_TRUNCATED, > SCAN_PAGE_HAS_PRIVATE, > + SCAN_COPY_MC, You need to update the tracepoint in include/trace/events/huge_memory.h to include the new result. > }; > > #define CREATE_TRACE_POINTS > @@ -739,44 +740,98 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > return 0; > } > > -static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > - struct vm_area_struct *vma, > - unsigned long address, > - spinlock_t *ptl, > - struct list_head *compound_pagelist) > +/* Better to use "/**" so that it could be converted to kernel doc. > + * __collapse_huge_page_copy - attempts to copy memory contents from normal > + * pages to a hugepage. Cleanup the normal pages if copying succeeds; > + * otherwise restore the original pmd page table. Returns true if copying > + * succeeds, otherwise returns false. > + * > + * @pte: starting of the PTEs to copy from > + * @page: the new hugepage to copy contents to > + * @pmd: pointer to the new hugepage's PMD > + * @rollback: the original normal PTEs' PMD You may not need pmd and rollback, please see the below comments for the reason. > + * @address: starting address to copy > + * @pte_ptl: lock on normal pages' PTEs > + * @compound_pagelist: list that stores compound pages > + */ > +static bool __collapse_huge_page_copy(pte_t *pte, > + struct page *page, > + pmd_t *pmd, > + pmd_t rollback, > + struct vm_area_struct *vma, > + unsigned long address, > + spinlock_t *pte_ptl, > + struct list_head *compound_pagelist) > { > struct page *src_page, *tmp; > pte_t *_pte; > - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; > - _pte++, page++, address += PAGE_SIZE) { > - pte_t pteval = *_pte; > + pte_t pteval; > + unsigned long _address; > + spinlock_t *pmd_ptl; > + bool copy_succeeded = true; > > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > + /* > + * Copying pages' contents is subject to memory poison at any iteration. > + */ > + for (_pte = pte, _address = address; > + _pte < pte + HPAGE_PMD_NR; > + _pte++, page++, _address += PAGE_SIZE) { > + pteval = *_pte; > + > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) > clear_user_highpage(page, address); > - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > - if (is_zero_pfn(pte_pfn(pteval))) { > - /* > - * ptl mostly unnecessary. > - */ > - spin_lock(ptl); > - ptep_clear(vma->vm_mm, address, _pte); > - spin_unlock(ptl); > + else { > + src_page = pte_page(pteval); > + if (copy_highpage_mc(page, src_page)) { > + copy_succeeded = false; > + break; > + } > + } > + } > + > + if (!copy_succeeded) { > + /* > + * Copying failed, re-establish the regular PMD that > + * points to regular page table. Since PTEs are still > + * isolated and locked, acquiring anon_vma_lock is unnecessary. > + */ > + pmd_ptl = pmd_lock(vma->vm_mm, pmd); > + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback)); > + spin_unlock(pmd_ptl); > + } I think the above section could be moved to out of __collapse_huge_page_copy(), just like what is done after __collapse_huge_page_isolate() is failed. You don't have to restore the pmd here since khugepaged holds write mmap_lock, there can't be page fault running in parallel. Hence you don't have to add pmd and rollback parameters to __collapse_huge_page_copy(). > + > + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR; > + _pte++, _address += PAGE_SIZE) { > + pteval = *_pte; > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > + if (copy_succeeded) { > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > + if (is_zero_pfn(pte_pfn(pteval))) { > + /* > + * ptl mostly unnecessary. > + */ > + spin_lock(pte_ptl); > + pte_clear(vma->vm_mm, _address, _pte); > + spin_unlock(pte_ptl); > + } > } > } else { > src_page = pte_page(pteval); > - copy_user_highpage(page, src_page, address, vma); > if (!PageCompound(src_page)) > release_pte_page(src_page); > - /* > - * ptl mostly unnecessary, but preempt has to > - * be disabled to update the per-cpu stats > - * inside page_remove_rmap(). > - */ > - spin_lock(ptl); > - ptep_clear(vma->vm_mm, address, _pte); > - page_remove_rmap(src_page, false); > - spin_unlock(ptl); > - free_page_and_swap_cache(src_page); > + > + if (copy_succeeded) { > + /* > + * ptl mostly unnecessary, but preempt has to > + * be disabled to update the per-cpu stats > + * inside page_remove_rmap(). > + */ > + spin_lock(pte_ptl); > + pte_clear(vma->vm_mm, _address, _pte); > + page_remove_rmap(src_page, false); > + spin_unlock(pte_ptl); > + free_page_and_swap_cache(src_page); > + } > } > } > > @@ -784,6 +839,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > list_del(&src_page->lru); > release_pte_page(src_page); > } > + > + return copy_succeeded; > } > > static void khugepaged_alloc_sleep(void) > @@ -1066,6 +1123,7 @@ static void collapse_huge_page(struct mm_struct *mm, > struct vm_area_struct *vma; > struct mmu_notifier_range range; > gfp_t gfp; > + bool copied = false; > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > @@ -1177,9 +1235,13 @@ static void collapse_huge_page(struct mm_struct *mm, > */ > anon_vma_unlock_write(vma->anon_vma); > > - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, > - &compound_pagelist); > + copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd, > + vma, address, pte_ptl, &compound_pagelist); > pte_unmap(pte); > + if (!copied) { > + result = SCAN_COPY_MC; > + goto out_up_write; > + } > /* > * spin_lock() below is not the equivalent of smp_wmb(), but > * the smp_wmb() inside __SetPageUptodate() can be reused to > @@ -1364,9 +1426,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > pte_unmap_unlock(pte, ptl); > if (ret) { > node = khugepaged_find_target_node(); > - /* collapse_huge_page will return with the mmap_lock released */ > - collapse_huge_page(mm, address, hpage, node, > - referenced, unmapped); > + /* > + * collapse_huge_page will return with the mmap_r+w_lock released. > + * It is uncertain if *hpage is NULL or not when collapse_huge_page > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > + * in khugepaged_scan_mm_slot, then *hpage will be freed > + * if collapse failed. > + */ > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > } > out: > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > @@ -2168,6 +2235,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > khugepaged_scan_file(mm, file, pgoff, hpage); > fput(file); > } else { > + /* > + * mmap_read_lock is > + * 1) released if both scan and collapse succeeded; > + * 2) still held if either scan or collapse failed. The #2 doesn't look correct. Even though collapse is failed, the mmap_lock is released as long as scan is succeeded. IIUC the collapse does: read unlock (passed in by scan) read lock read unlock write lock write unlock > + */ > ret = khugepaged_scan_pmd(mm, vma, > khugepaged_scan.address, > hpage); > -- > 2.35.1.1178.g4f1659d476-goog >
On Fri, Apr 29, 2022 at 3:15 PM Yang Shi <shy828301@gmail.com> wrote: > > On Thu, Apr 28, 2022 at 5:09 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > Make __collapse_huge_page_copy return whether > > collapsing/copying anonymous pages succeeded, > > and make collapse_huge_page handle the return status. > > > > Break existing PTE scan loop into two for-loops. > > The first loop copies source pages into target huge page, > > and can fail gracefully when running into memory errors in > > source pages. Roll back the page table and page states > > in the 2nd loop when copying failed: > > 1) re-establish the PTEs-to-PMD connection. > > 2) release pages back to their LRU list. > > Could you please include a changelog next time? It is really helpful > for reviewers. Of course, I will include change logs for both v2 + v3 changes. > > > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > --- > > include/linux/highmem.h | 19 ++++++ > > mm/khugepaged.c | 138 ++++++++++++++++++++++++++++++---------- > > 2 files changed, 124 insertions(+), 33 deletions(-) > > > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > > index 39bb9b47fa9cd..0ccb1e92c4b06 100644 > > --- a/include/linux/highmem.h > > +++ b/include/linux/highmem.h > > @@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from) > > > > #endif > > > > +/* > > + * Machine check exception handled version of copy_highpage. > > + * Return true if copying page content failed; otherwise false. > > + * Note handling #MC requires arch opt-in. > > + */ > > +static inline bool copy_highpage_mc(struct page *to, struct page *from) > > +{ > > + char *vfrom, *vto; > > + unsigned long ret; > > + > > + vfrom = kmap_local_page(from); > > + vto = kmap_local_page(to); > > + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE); > > + kunmap_local(vto); > > + kunmap_local(vfrom); > > + > > + return ret > 0; > > +} > > + > > static inline void memcpy_page(struct page *dst_page, size_t dst_off, > > struct page *src_page, size_t src_off, > > size_t len) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 131492fd1148b..8e69a0640e551 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -52,6 +52,7 @@ enum scan_result { > > SCAN_CGROUP_CHARGE_FAIL, > > SCAN_TRUNCATED, > > SCAN_PAGE_HAS_PRIVATE, > > + SCAN_COPY_MC, > > You need to update the tracepoint in > include/trace/events/huge_memory.h to include the new result. Will add tracepoint in v3. > > > }; > > > > #define CREATE_TRACE_POINTS > > @@ -739,44 +740,98 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > > return 0; > > } > > > > -static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > - struct vm_area_struct *vma, > > - unsigned long address, > > - spinlock_t *ptl, > > - struct list_head *compound_pagelist) > > +/* > > Better to use "/**" so that it could be converted to kernel doc. Will update in v3. > > > + * __collapse_huge_page_copy - attempts to copy memory contents from normal > > + * pages to a hugepage. Cleanup the normal pages if copying succeeds; > > + * otherwise restore the original pmd page table. Returns true if copying > > + * succeeds, otherwise returns false. > > + * > > + * @pte: starting of the PTEs to copy from > > + * @page: the new hugepage to copy contents to > > + * @pmd: pointer to the new hugepage's PMD > > + * @rollback: the original normal PTEs' PMD > > You may not need pmd and rollback, please see the below comments for the reason. > > > + * @address: starting address to copy > > + * @pte_ptl: lock on normal pages' PTEs > > + * @compound_pagelist: list that stores compound pages > > + */ > > +static bool __collapse_huge_page_copy(pte_t *pte, > > + struct page *page, > > + pmd_t *pmd, > > + pmd_t rollback, > > + struct vm_area_struct *vma, > > + unsigned long address, > > + spinlock_t *pte_ptl, > > + struct list_head *compound_pagelist) > > { > > struct page *src_page, *tmp; > > pte_t *_pte; > > - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; > > - _pte++, page++, address += PAGE_SIZE) { > > - pte_t pteval = *_pte; > > + pte_t pteval; > > + unsigned long _address; > > + spinlock_t *pmd_ptl; > > + bool copy_succeeded = true; > > > > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > + /* > > + * Copying pages' contents is subject to memory poison at any iteration. > > + */ > > + for (_pte = pte, _address = address; > > + _pte < pte + HPAGE_PMD_NR; > > + _pte++, page++, _address += PAGE_SIZE) { > > + pteval = *_pte; > > + > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) > > clear_user_highpage(page, address); > > - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > - if (is_zero_pfn(pte_pfn(pteval))) { > > - /* > > - * ptl mostly unnecessary. > > - */ > > - spin_lock(ptl); > > - ptep_clear(vma->vm_mm, address, _pte); > > - spin_unlock(ptl); > > + else { > > + src_page = pte_page(pteval); > > + if (copy_highpage_mc(page, src_page)) { > > + copy_succeeded = false; > > + break; > > + } > > + } > > + } > > + > > + if (!copy_succeeded) { > > + /* > > + * Copying failed, re-establish the regular PMD that > > + * points to regular page table. Since PTEs are still > > + * isolated and locked, acquiring anon_vma_lock is unnecessary. > > + */ > > + pmd_ptl = pmd_lock(vma->vm_mm, pmd); > > + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback)); > > + spin_unlock(pmd_ptl); > > + } > > I think the above section could be moved to out of > __collapse_huge_page_copy(), just like what is done after > __collapse_huge_page_isolate() is failed. > > You don't have to restore the pmd here since khugepaged holds write > mmap_lock, there can't be page fault running in parallel. Hence you > don't have to add pmd and rollback parameters to > __collapse_huge_page_copy(). > The reason I re-establish the pmd table here is to avoid anon_vma_lock_write since here PTEs are still isolated and locked. Are you implying that, we should do the PMD re-establishment after PTEs released? and more importantly, with or without holding the anon_vma_lock_write? > > + > > + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR; > > + _pte++, _address += PAGE_SIZE) { > > + pteval = *_pte; > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > + if (copy_succeeded) { > > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > + if (is_zero_pfn(pte_pfn(pteval))) { > > + /* > > + * ptl mostly unnecessary. > > + */ > > + spin_lock(pte_ptl); > > + pte_clear(vma->vm_mm, _address, _pte); > > + spin_unlock(pte_ptl); > > + } > > } > > } else { > > src_page = pte_page(pteval); > > - copy_user_highpage(page, src_page, address, vma); > > if (!PageCompound(src_page)) > > release_pte_page(src_page); > > - /* > > - * ptl mostly unnecessary, but preempt has to > > - * be disabled to update the per-cpu stats > > - * inside page_remove_rmap(). > > - */ > > - spin_lock(ptl); > > - ptep_clear(vma->vm_mm, address, _pte); > > - page_remove_rmap(src_page, false); > > - spin_unlock(ptl); > > - free_page_and_swap_cache(src_page); > > + > > + if (copy_succeeded) { > > + /* > > + * ptl mostly unnecessary, but preempt has to > > + * be disabled to update the per-cpu stats > > + * inside page_remove_rmap(). > > + */ > > + spin_lock(pte_ptl); > > + pte_clear(vma->vm_mm, _address, _pte); > > + page_remove_rmap(src_page, false); > > + spin_unlock(pte_ptl); > > + free_page_and_swap_cache(src_page); > > + } > > } > > } > > > > @@ -784,6 +839,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > list_del(&src_page->lru); > > release_pte_page(src_page); > > } > > + > > + return copy_succeeded; > > } > > > > static void khugepaged_alloc_sleep(void) > > @@ -1066,6 +1123,7 @@ static void collapse_huge_page(struct mm_struct *mm, > > struct vm_area_struct *vma; > > struct mmu_notifier_range range; > > gfp_t gfp; > > + bool copied = false; > > > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > > > @@ -1177,9 +1235,13 @@ static void collapse_huge_page(struct mm_struct *mm, > > */ > > anon_vma_unlock_write(vma->anon_vma); > > > > - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, > > - &compound_pagelist); > > + copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd, > > + vma, address, pte_ptl, &compound_pagelist); > > pte_unmap(pte); > > + if (!copied) { > > + result = SCAN_COPY_MC; > > + goto out_up_write; > > + } > > /* > > * spin_lock() below is not the equivalent of smp_wmb(), but > > * the smp_wmb() inside __SetPageUptodate() can be reused to > > @@ -1364,9 +1426,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > > pte_unmap_unlock(pte, ptl); > > if (ret) { > > node = khugepaged_find_target_node(); > > - /* collapse_huge_page will return with the mmap_lock released */ > > - collapse_huge_page(mm, address, hpage, node, > > - referenced, unmapped); > > + /* > > + * collapse_huge_page will return with the mmap_r+w_lock released. > > + * It is uncertain if *hpage is NULL or not when collapse_huge_page > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > + * if collapse failed. > > + */ > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > } > > out: > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > @@ -2168,6 +2235,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > > khugepaged_scan_file(mm, file, pgoff, hpage); > > fput(file); > > } else { > > + /* > > + * mmap_read_lock is > > + * 1) released if both scan and collapse succeeded; > > + * 2) still held if either scan or collapse failed. > > The #2 doesn't look correct. Even though collapse is failed, the > mmap_lock is released as long as scan is succeeded. > > IIUC the collapse does: > read unlock (passed in by scan) > read lock > read unlock > write lock > write unlock > You are right! I will update this comment block in v3. > > + */ > > ret = khugepaged_scan_pmd(mm, vma, > > khugepaged_scan.address, > > hpage); > > -- > > 2.35.1.1178.g4f1659d476-goog > >
On Fri, May 20, 2022 at 4:34 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > On Fri, Apr 29, 2022 at 3:15 PM Yang Shi <shy828301@gmail.com> wrote: > > > > On Thu, Apr 28, 2022 at 5:09 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > > > Make __collapse_huge_page_copy return whether > > > collapsing/copying anonymous pages succeeded, > > > and make collapse_huge_page handle the return status. > > > > > > Break existing PTE scan loop into two for-loops. > > > The first loop copies source pages into target huge page, > > > and can fail gracefully when running into memory errors in > > > source pages. Roll back the page table and page states > > > in the 2nd loop when copying failed: > > > 1) re-establish the PTEs-to-PMD connection. > > > 2) release pages back to their LRU list. > > > > Could you please include a changelog next time? It is really helpful > > for reviewers. > > Of course, I will include change logs for both v2 + v3 changes. > > > > > > > > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > > --- > > > include/linux/highmem.h | 19 ++++++ > > > mm/khugepaged.c | 138 ++++++++++++++++++++++++++++++---------- > > > 2 files changed, 124 insertions(+), 33 deletions(-) > > > > > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > > > index 39bb9b47fa9cd..0ccb1e92c4b06 100644 > > > --- a/include/linux/highmem.h > > > +++ b/include/linux/highmem.h > > > @@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from) > > > > > > #endif > > > > > > +/* > > > + * Machine check exception handled version of copy_highpage. > > > + * Return true if copying page content failed; otherwise false. > > > + * Note handling #MC requires arch opt-in. > > > + */ > > > +static inline bool copy_highpage_mc(struct page *to, struct page *from) > > > +{ > > > + char *vfrom, *vto; > > > + unsigned long ret; > > > + > > > + vfrom = kmap_local_page(from); > > > + vto = kmap_local_page(to); > > > + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE); > > > + kunmap_local(vto); > > > + kunmap_local(vfrom); > > > + > > > + return ret > 0; > > > +} > > > + > > > static inline void memcpy_page(struct page *dst_page, size_t dst_off, > > > struct page *src_page, size_t src_off, > > > size_t len) > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > index 131492fd1148b..8e69a0640e551 100644 > > > --- a/mm/khugepaged.c > > > +++ b/mm/khugepaged.c > > > @@ -52,6 +52,7 @@ enum scan_result { > > > SCAN_CGROUP_CHARGE_FAIL, > > > SCAN_TRUNCATED, > > > SCAN_PAGE_HAS_PRIVATE, > > > + SCAN_COPY_MC, > > > > You need to update the tracepoint in > > include/trace/events/huge_memory.h to include the new result. > > Will add tracepoint in v3. > > > > > > }; > > > > > > #define CREATE_TRACE_POINTS > > > @@ -739,44 +740,98 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > > > return 0; > > > } > > > > > > -static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > - struct vm_area_struct *vma, > > > - unsigned long address, > > > - spinlock_t *ptl, > > > - struct list_head *compound_pagelist) > > > +/* > > > > Better to use "/**" so that it could be converted to kernel doc. > > Will update in v3. > > > > > > + * __collapse_huge_page_copy - attempts to copy memory contents from normal > > > + * pages to a hugepage. Cleanup the normal pages if copying succeeds; > > > + * otherwise restore the original pmd page table. Returns true if copying > > > + * succeeds, otherwise returns false. > > > + * > > > + * @pte: starting of the PTEs to copy from > > > + * @page: the new hugepage to copy contents to > > > + * @pmd: pointer to the new hugepage's PMD > > > + * @rollback: the original normal PTEs' PMD > > > > You may not need pmd and rollback, please see the below comments for the reason. > > > > > + * @address: starting address to copy > > > + * @pte_ptl: lock on normal pages' PTEs > > > + * @compound_pagelist: list that stores compound pages > > > + */ > > > +static bool __collapse_huge_page_copy(pte_t *pte, > > > + struct page *page, > > > + pmd_t *pmd, > > > + pmd_t rollback, > > > + struct vm_area_struct *vma, > > > + unsigned long address, > > > + spinlock_t *pte_ptl, > > > + struct list_head *compound_pagelist) > > > { > > > struct page *src_page, *tmp; > > > pte_t *_pte; > > > - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; > > > - _pte++, page++, address += PAGE_SIZE) { > > > - pte_t pteval = *_pte; > > > + pte_t pteval; > > > + unsigned long _address; > > > + spinlock_t *pmd_ptl; > > > + bool copy_succeeded = true; > > > > > > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > + /* > > > + * Copying pages' contents is subject to memory poison at any iteration. > > > + */ > > > + for (_pte = pte, _address = address; > > > + _pte < pte + HPAGE_PMD_NR; > > > + _pte++, page++, _address += PAGE_SIZE) { > > > + pteval = *_pte; > > > + > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) > > > clear_user_highpage(page, address); > > > - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > - if (is_zero_pfn(pte_pfn(pteval))) { > > > - /* > > > - * ptl mostly unnecessary. > > > - */ > > > - spin_lock(ptl); > > > - ptep_clear(vma->vm_mm, address, _pte); > > > - spin_unlock(ptl); > > > + else { > > > + src_page = pte_page(pteval); > > > + if (copy_highpage_mc(page, src_page)) { > > > + copy_succeeded = false; > > > + break; > > > + } > > > + } > > > + } > > > + > > > + if (!copy_succeeded) { > > > + /* > > > + * Copying failed, re-establish the regular PMD that > > > + * points to regular page table. Since PTEs are still > > > + * isolated and locked, acquiring anon_vma_lock is unnecessary. > > > + */ > > > + pmd_ptl = pmd_lock(vma->vm_mm, pmd); > > > + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback)); > > > + spin_unlock(pmd_ptl); > > > + } > > > > I think the above section could be moved to out of > > __collapse_huge_page_copy(), just like what is done after > > __collapse_huge_page_isolate() is failed. > > > > You don't have to restore the pmd here since khugepaged holds write > > mmap_lock, there can't be page fault running in parallel. Hence you > > don't have to add pmd and rollback parameters to > > __collapse_huge_page_copy(). > > > > The reason I re-establish the pmd table here is to avoid anon_vma_lock_write > since here PTEs are still isolated and locked. Are you implying that, we should > do the PMD re-establishment after PTEs released? and more importantly, > with or without holding the anon_vma_lock_write? I think you mean "pages" are still isolated and locked. I see the point. If the pages are unisolated before PMD is restored, the parallel try_to_unmap/migrate() may fail prematurely. > > > > + > > > + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR; > > > + _pte++, _address += PAGE_SIZE) { > > > + pteval = *_pte; > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > + if (copy_succeeded) { > > > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > + if (is_zero_pfn(pte_pfn(pteval))) { > > > + /* > > > + * ptl mostly unnecessary. > > > + */ > > > + spin_lock(pte_ptl); > > > + pte_clear(vma->vm_mm, _address, _pte); > > > + spin_unlock(pte_ptl); > > > + } > > > } > > > } else { > > > src_page = pte_page(pteval); > > > - copy_user_highpage(page, src_page, address, vma); > > > if (!PageCompound(src_page)) > > > release_pte_page(src_page); > > > - /* > > > - * ptl mostly unnecessary, but preempt has to > > > - * be disabled to update the per-cpu stats > > > - * inside page_remove_rmap(). > > > - */ > > > - spin_lock(ptl); > > > - ptep_clear(vma->vm_mm, address, _pte); > > > - page_remove_rmap(src_page, false); > > > - spin_unlock(ptl); > > > - free_page_and_swap_cache(src_page); > > > + > > > + if (copy_succeeded) { > > > + /* > > > + * ptl mostly unnecessary, but preempt has to > > > + * be disabled to update the per-cpu stats > > > + * inside page_remove_rmap(). > > > + */ > > > + spin_lock(pte_ptl); > > > + pte_clear(vma->vm_mm, _address, _pte); > > > + page_remove_rmap(src_page, false); > > > + spin_unlock(pte_ptl); > > > + free_page_and_swap_cache(src_page); > > > + } > > > } > > > } > > > > > > @@ -784,6 +839,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > list_del(&src_page->lru); > > > release_pte_page(src_page); > > > } > > > + > > > + return copy_succeeded; > > > } > > > > > > static void khugepaged_alloc_sleep(void) > > > @@ -1066,6 +1123,7 @@ static void collapse_huge_page(struct mm_struct *mm, > > > struct vm_area_struct *vma; > > > struct mmu_notifier_range range; > > > gfp_t gfp; > > > + bool copied = false; > > > > > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > > > > > @@ -1177,9 +1235,13 @@ static void collapse_huge_page(struct mm_struct *mm, > > > */ > > > anon_vma_unlock_write(vma->anon_vma); > > > > > > - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, > > > - &compound_pagelist); > > > + copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd, > > > + vma, address, pte_ptl, &compound_pagelist); > > > pte_unmap(pte); > > > + if (!copied) { > > > + result = SCAN_COPY_MC; > > > + goto out_up_write; > > > + } > > > /* > > > * spin_lock() below is not the equivalent of smp_wmb(), but > > > * the smp_wmb() inside __SetPageUptodate() can be reused to > > > @@ -1364,9 +1426,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > > > pte_unmap_unlock(pte, ptl); > > > if (ret) { > > > node = khugepaged_find_target_node(); > > > - /* collapse_huge_page will return with the mmap_lock released */ > > > - collapse_huge_page(mm, address, hpage, node, > > > - referenced, unmapped); > > > + /* > > > + * collapse_huge_page will return with the mmap_r+w_lock released. > > > + * It is uncertain if *hpage is NULL or not when collapse_huge_page > > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > > + * if collapse failed. > > > + */ > > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > > } > > > out: > > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > > @@ -2168,6 +2235,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > > > khugepaged_scan_file(mm, file, pgoff, hpage); > > > fput(file); > > > } else { > > > + /* > > > + * mmap_read_lock is > > > + * 1) released if both scan and collapse succeeded; > > > + * 2) still held if either scan or collapse failed. > > > > The #2 doesn't look correct. Even though collapse is failed, the > > mmap_lock is released as long as scan is succeeded. > > > > IIUC the collapse does: > > read unlock (passed in by scan) > > read lock > > read unlock > > write lock > > write unlock > > > > You are right! I will update this comment block in v3. > > > > + */ > > > ret = khugepaged_scan_pmd(mm, vma, > > > khugepaged_scan.address, > > > hpage); > > > -- > > > 2.35.1.1178.g4f1659d476-goog > > >
On Mon, May 23, 2022 at 11:48 AM Yang Shi <shy828301@gmail.com> wrote: > > On Fri, May 20, 2022 at 4:34 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > On Fri, Apr 29, 2022 at 3:15 PM Yang Shi <shy828301@gmail.com> wrote: > > > > > > On Thu, Apr 28, 2022 at 5:09 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > > > > > Make __collapse_huge_page_copy return whether > > > > collapsing/copying anonymous pages succeeded, > > > > and make collapse_huge_page handle the return status. > > > > > > > > Break existing PTE scan loop into two for-loops. > > > > The first loop copies source pages into target huge page, > > > > and can fail gracefully when running into memory errors in > > > > source pages. Roll back the page table and page states > > > > in the 2nd loop when copying failed: > > > > 1) re-establish the PTEs-to-PMD connection. > > > > 2) release pages back to their LRU list. > > > > > > Could you please include a changelog next time? It is really helpful > > > for reviewers. > > > > Of course, I will include change logs for both v2 + v3 changes. > > > > > > > > > > > > > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > > > --- > > > > include/linux/highmem.h | 19 ++++++ > > > > mm/khugepaged.c | 138 ++++++++++++++++++++++++++++++---------- > > > > 2 files changed, 124 insertions(+), 33 deletions(-) > > > > > > > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > > > > index 39bb9b47fa9cd..0ccb1e92c4b06 100644 > > > > --- a/include/linux/highmem.h > > > > +++ b/include/linux/highmem.h > > > > @@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from) > > > > > > > > #endif > > > > > > > > +/* > > > > + * Machine check exception handled version of copy_highpage. > > > > + * Return true if copying page content failed; otherwise false. > > > > + * Note handling #MC requires arch opt-in. > > > > + */ > > > > +static inline bool copy_highpage_mc(struct page *to, struct page *from) > > > > +{ > > > > + char *vfrom, *vto; > > > > + unsigned long ret; > > > > + > > > > + vfrom = kmap_local_page(from); > > > > + vto = kmap_local_page(to); > > > > + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE); > > > > + kunmap_local(vto); > > > > + kunmap_local(vfrom); > > > > + > > > > + return ret > 0; > > > > +} > > > > + > > > > static inline void memcpy_page(struct page *dst_page, size_t dst_off, > > > > struct page *src_page, size_t src_off, > > > > size_t len) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > > index 131492fd1148b..8e69a0640e551 100644 > > > > --- a/mm/khugepaged.c > > > > +++ b/mm/khugepaged.c > > > > @@ -52,6 +52,7 @@ enum scan_result { > > > > SCAN_CGROUP_CHARGE_FAIL, > > > > SCAN_TRUNCATED, > > > > SCAN_PAGE_HAS_PRIVATE, > > > > + SCAN_COPY_MC, > > > > > > You need to update the tracepoint in > > > include/trace/events/huge_memory.h to include the new result. > > > > Will add tracepoint in v3. > > > > > > > > > }; > > > > > > > > #define CREATE_TRACE_POINTS > > > > @@ -739,44 +740,98 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > > > > return 0; > > > > } > > > > > > > > -static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > > - struct vm_area_struct *vma, > > > > - unsigned long address, > > > > - spinlock_t *ptl, > > > > - struct list_head *compound_pagelist) > > > > +/* > > > > > > Better to use "/**" so that it could be converted to kernel doc. > > > > Will update in v3. > > > > > > > > > + * __collapse_huge_page_copy - attempts to copy memory contents from normal > > > > + * pages to a hugepage. Cleanup the normal pages if copying succeeds; > > > > + * otherwise restore the original pmd page table. Returns true if copying > > > > + * succeeds, otherwise returns false. > > > > + * > > > > + * @pte: starting of the PTEs to copy from > > > > + * @page: the new hugepage to copy contents to > > > > + * @pmd: pointer to the new hugepage's PMD > > > > + * @rollback: the original normal PTEs' PMD > > > > > > You may not need pmd and rollback, please see the below comments for the reason. > > > > > > > + * @address: starting address to copy > > > > + * @pte_ptl: lock on normal pages' PTEs > > > > + * @compound_pagelist: list that stores compound pages > > > > + */ > > > > +static bool __collapse_huge_page_copy(pte_t *pte, > > > > + struct page *page, > > > > + pmd_t *pmd, > > > > + pmd_t rollback, > > > > + struct vm_area_struct *vma, > > > > + unsigned long address, > > > > + spinlock_t *pte_ptl, > > > > + struct list_head *compound_pagelist) > > > > { > > > > struct page *src_page, *tmp; > > > > pte_t *_pte; > > > > - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; > > > > - _pte++, page++, address += PAGE_SIZE) { > > > > - pte_t pteval = *_pte; > > > > + pte_t pteval; > > > > + unsigned long _address; > > > > + spinlock_t *pmd_ptl; > > > > + bool copy_succeeded = true; > > > > > > > > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > > + /* > > > > + * Copying pages' contents is subject to memory poison at any iteration. > > > > + */ > > > > + for (_pte = pte, _address = address; > > > > + _pte < pte + HPAGE_PMD_NR; > > > > + _pte++, page++, _address += PAGE_SIZE) { > > > > + pteval = *_pte; > > > > + > > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) > > > > clear_user_highpage(page, address); > > > > - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > > - if (is_zero_pfn(pte_pfn(pteval))) { > > > > - /* > > > > - * ptl mostly unnecessary. > > > > - */ > > > > - spin_lock(ptl); > > > > - ptep_clear(vma->vm_mm, address, _pte); > > > > - spin_unlock(ptl); > > > > + else { > > > > + src_page = pte_page(pteval); > > > > + if (copy_highpage_mc(page, src_page)) { > > > > + copy_succeeded = false; > > > > + break; > > > > + } > > > > + } > > > > + } > > > > + > > > > + if (!copy_succeeded) { > > > > + /* > > > > + * Copying failed, re-establish the regular PMD that > > > > + * points to regular page table. Since PTEs are still > > > > + * isolated and locked, acquiring anon_vma_lock is unnecessary. > > > > + */ > > > > + pmd_ptl = pmd_lock(vma->vm_mm, pmd); > > > > + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback)); > > > > + spin_unlock(pmd_ptl); > > > > + } > > > > > > I think the above section could be moved to out of > > > __collapse_huge_page_copy(), just like what is done after > > > __collapse_huge_page_isolate() is failed. > > > > > > You don't have to restore the pmd here since khugepaged holds write > > > mmap_lock, there can't be page fault running in parallel. Hence you > > > don't have to add pmd and rollback parameters to > > > __collapse_huge_page_copy(). > > > > > > > The reason I re-establish the pmd table here is to avoid anon_vma_lock_write > > since here PTEs are still isolated and locked. Are you implying that, we should > > do the PMD re-establishment after PTEs released? and more importantly, > > with or without holding the anon_vma_lock_write? > > I think you mean "pages" are still isolated and locked. I see the > point. If the pages are unisolated before PMD is restored, the > parallel try_to_unmap/migrate() may fail prematurely. > Yes, I mean "pages". Therefore I think PMD re-establishing should happen inside __collapse_huge_page_copy as one of the rollback operations (and requiring passing @pmd and @rollback). Agree? > > > > > > + > > > > + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR; > > > > + _pte++, _address += PAGE_SIZE) { > > > > + pteval = *_pte; > > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > > + if (copy_succeeded) { > > > > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > > + if (is_zero_pfn(pte_pfn(pteval))) { > > > > + /* > > > > + * ptl mostly unnecessary. > > > > + */ > > > > + spin_lock(pte_ptl); > > > > + pte_clear(vma->vm_mm, _address, _pte); > > > > + spin_unlock(pte_ptl); > > > > + } > > > > } > > > > } else { > > > > src_page = pte_page(pteval); > > > > - copy_user_highpage(page, src_page, address, vma); > > > > if (!PageCompound(src_page)) > > > > release_pte_page(src_page); > > > > - /* > > > > - * ptl mostly unnecessary, but preempt has to > > > > - * be disabled to update the per-cpu stats > > > > - * inside page_remove_rmap(). > > > > - */ > > > > - spin_lock(ptl); > > > > - ptep_clear(vma->vm_mm, address, _pte); > > > > - page_remove_rmap(src_page, false); > > > > - spin_unlock(ptl); > > > > - free_page_and_swap_cache(src_page); > > > > + > > > > + if (copy_succeeded) { > > > > + /* > > > > + * ptl mostly unnecessary, but preempt has to > > > > + * be disabled to update the per-cpu stats > > > > + * inside page_remove_rmap(). > > > > + */ > > > > + spin_lock(pte_ptl); > > > > + pte_clear(vma->vm_mm, _address, _pte); > > > > + page_remove_rmap(src_page, false); > > > > + spin_unlock(pte_ptl); > > > > + free_page_and_swap_cache(src_page); > > > > + } > > > > } > > > > } > > > > > > > > @@ -784,6 +839,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > > list_del(&src_page->lru); > > > > release_pte_page(src_page); > > > > } > > > > + > > > > + return copy_succeeded; > > > > } > > > > > > > > static void khugepaged_alloc_sleep(void) > > > > @@ -1066,6 +1123,7 @@ static void collapse_huge_page(struct mm_struct *mm, > > > > struct vm_area_struct *vma; > > > > struct mmu_notifier_range range; > > > > gfp_t gfp; > > > > + bool copied = false; > > > > > > > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > > > > > > > @@ -1177,9 +1235,13 @@ static void collapse_huge_page(struct mm_struct *mm, > > > > */ > > > > anon_vma_unlock_write(vma->anon_vma); > > > > > > > > - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, > > > > - &compound_pagelist); > > > > + copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd, > > > > + vma, address, pte_ptl, &compound_pagelist); > > > > pte_unmap(pte); > > > > + if (!copied) { > > > > + result = SCAN_COPY_MC; > > > > + goto out_up_write; > > > > + } > > > > /* > > > > * spin_lock() below is not the equivalent of smp_wmb(), but > > > > * the smp_wmb() inside __SetPageUptodate() can be reused to > > > > @@ -1364,9 +1426,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > > > > pte_unmap_unlock(pte, ptl); > > > > if (ret) { > > > > node = khugepaged_find_target_node(); > > > > - /* collapse_huge_page will return with the mmap_lock released */ > > > > - collapse_huge_page(mm, address, hpage, node, > > > > - referenced, unmapped); > > > > + /* > > > > + * collapse_huge_page will return with the mmap_r+w_lock released. > > > > + * It is uncertain if *hpage is NULL or not when collapse_huge_page > > > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > > > + * if collapse failed. > > > > + */ > > > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > > > } > > > > out: > > > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > > > @@ -2168,6 +2235,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > > > > khugepaged_scan_file(mm, file, pgoff, hpage); > > > > fput(file); > > > > } else { > > > > + /* > > > > + * mmap_read_lock is > > > > + * 1) released if both scan and collapse succeeded; > > > > + * 2) still held if either scan or collapse failed. > > > > > > The #2 doesn't look correct. Even though collapse is failed, the > > > mmap_lock is released as long as scan is succeeded. > > > > > > IIUC the collapse does: > > > read unlock (passed in by scan) > > > read lock > > > read unlock > > > write lock > > > write unlock > > > > > > > You are right! I will update this comment block in v3. > > > > > > + */ > > > > ret = khugepaged_scan_pmd(mm, vma, > > > > khugepaged_scan.address, > > > > hpage); > > > > -- > > > > 2.35.1.1178.g4f1659d476-goog > > > >
On Mon, May 23, 2022 at 12:02 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > On Mon, May 23, 2022 at 11:48 AM Yang Shi <shy828301@gmail.com> wrote: > > > > On Fri, May 20, 2022 at 4:34 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > > > On Fri, Apr 29, 2022 at 3:15 PM Yang Shi <shy828301@gmail.com> wrote: > > > > > > > > On Thu, Apr 28, 2022 at 5:09 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > > > > > > > Make __collapse_huge_page_copy return whether > > > > > collapsing/copying anonymous pages succeeded, > > > > > and make collapse_huge_page handle the return status. > > > > > > > > > > Break existing PTE scan loop into two for-loops. > > > > > The first loop copies source pages into target huge page, > > > > > and can fail gracefully when running into memory errors in > > > > > source pages. Roll back the page table and page states > > > > > in the 2nd loop when copying failed: > > > > > 1) re-establish the PTEs-to-PMD connection. > > > > > 2) release pages back to their LRU list. > > > > > > > > Could you please include a changelog next time? It is really helpful > > > > for reviewers. > > > > > > Of course, I will include change logs for both v2 + v3 changes. > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > > > > --- > > > > > include/linux/highmem.h | 19 ++++++ > > > > > mm/khugepaged.c | 138 ++++++++++++++++++++++++++++++---------- > > > > > 2 files changed, 124 insertions(+), 33 deletions(-) > > > > > > > > > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > > > > > index 39bb9b47fa9cd..0ccb1e92c4b06 100644 > > > > > --- a/include/linux/highmem.h > > > > > +++ b/include/linux/highmem.h > > > > > @@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from) > > > > > > > > > > #endif > > > > > > > > > > +/* > > > > > + * Machine check exception handled version of copy_highpage. > > > > > + * Return true if copying page content failed; otherwise false. > > > > > + * Note handling #MC requires arch opt-in. > > > > > + */ > > > > > +static inline bool copy_highpage_mc(struct page *to, struct page *from) > > > > > +{ > > > > > + char *vfrom, *vto; > > > > > + unsigned long ret; > > > > > + > > > > > + vfrom = kmap_local_page(from); > > > > > + vto = kmap_local_page(to); > > > > > + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE); > > > > > + kunmap_local(vto); > > > > > + kunmap_local(vfrom); > > > > > + > > > > > + return ret > 0; > > > > > +} > > > > > + > > > > > static inline void memcpy_page(struct page *dst_page, size_t dst_off, > > > > > struct page *src_page, size_t src_off, > > > > > size_t len) > > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > > > index 131492fd1148b..8e69a0640e551 100644 > > > > > --- a/mm/khugepaged.c > > > > > +++ b/mm/khugepaged.c > > > > > @@ -52,6 +52,7 @@ enum scan_result { > > > > > SCAN_CGROUP_CHARGE_FAIL, > > > > > SCAN_TRUNCATED, > > > > > SCAN_PAGE_HAS_PRIVATE, > > > > > + SCAN_COPY_MC, > > > > > > > > You need to update the tracepoint in > > > > include/trace/events/huge_memory.h to include the new result. > > > > > > Will add tracepoint in v3. > > > > > > > > > > > > }; > > > > > > > > > > #define CREATE_TRACE_POINTS > > > > > @@ -739,44 +740,98 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > > > > > return 0; > > > > > } > > > > > > > > > > -static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > > > - struct vm_area_struct *vma, > > > > > - unsigned long address, > > > > > - spinlock_t *ptl, > > > > > - struct list_head *compound_pagelist) > > > > > +/* > > > > > > > > Better to use "/**" so that it could be converted to kernel doc. > > > > > > Will update in v3. > > > > > > > > > > > > + * __collapse_huge_page_copy - attempts to copy memory contents from normal > > > > > + * pages to a hugepage. Cleanup the normal pages if copying succeeds; > > > > > + * otherwise restore the original pmd page table. Returns true if copying > > > > > + * succeeds, otherwise returns false. > > > > > + * > > > > > + * @pte: starting of the PTEs to copy from > > > > > + * @page: the new hugepage to copy contents to > > > > > + * @pmd: pointer to the new hugepage's PMD > > > > > + * @rollback: the original normal PTEs' PMD > > > > > > > > You may not need pmd and rollback, please see the below comments for the reason. > > > > > > > > > + * @address: starting address to copy > > > > > + * @pte_ptl: lock on normal pages' PTEs > > > > > + * @compound_pagelist: list that stores compound pages > > > > > + */ > > > > > +static bool __collapse_huge_page_copy(pte_t *pte, > > > > > + struct page *page, > > > > > + pmd_t *pmd, > > > > > + pmd_t rollback, > > > > > + struct vm_area_struct *vma, > > > > > + unsigned long address, > > > > > + spinlock_t *pte_ptl, > > > > > + struct list_head *compound_pagelist) > > > > > { > > > > > struct page *src_page, *tmp; > > > > > pte_t *_pte; > > > > > - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; > > > > > - _pte++, page++, address += PAGE_SIZE) { > > > > > - pte_t pteval = *_pte; > > > > > + pte_t pteval; > > > > > + unsigned long _address; > > > > > + spinlock_t *pmd_ptl; > > > > > + bool copy_succeeded = true; > > > > > > > > > > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > > > + /* > > > > > + * Copying pages' contents is subject to memory poison at any iteration. > > > > > + */ > > > > > + for (_pte = pte, _address = address; > > > > > + _pte < pte + HPAGE_PMD_NR; > > > > > + _pte++, page++, _address += PAGE_SIZE) { > > > > > + pteval = *_pte; > > > > > + > > > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) > > > > > clear_user_highpage(page, address); > > > > > - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > > > - if (is_zero_pfn(pte_pfn(pteval))) { > > > > > - /* > > > > > - * ptl mostly unnecessary. > > > > > - */ > > > > > - spin_lock(ptl); > > > > > - ptep_clear(vma->vm_mm, address, _pte); > > > > > - spin_unlock(ptl); > > > > > + else { > > > > > + src_page = pte_page(pteval); > > > > > + if (copy_highpage_mc(page, src_page)) { > > > > > + copy_succeeded = false; > > > > > + break; > > > > > + } > > > > > + } > > > > > + } > > > > > + > > > > > + if (!copy_succeeded) { > > > > > + /* > > > > > + * Copying failed, re-establish the regular PMD that > > > > > + * points to regular page table. Since PTEs are still > > > > > + * isolated and locked, acquiring anon_vma_lock is unnecessary. > > > > > + */ > > > > > + pmd_ptl = pmd_lock(vma->vm_mm, pmd); > > > > > + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback)); > > > > > + spin_unlock(pmd_ptl); > > > > > + } > > > > > > > > I think the above section could be moved to out of > > > > __collapse_huge_page_copy(), just like what is done after > > > > __collapse_huge_page_isolate() is failed. > > > > > > > > You don't have to restore the pmd here since khugepaged holds write > > > > mmap_lock, there can't be page fault running in parallel. Hence you > > > > don't have to add pmd and rollback parameters to > > > > __collapse_huge_page_copy(). > > > > > > > > > > The reason I re-establish the pmd table here is to avoid anon_vma_lock_write > > > since here PTEs are still isolated and locked. Are you implying that, we should > > > do the PMD re-establishment after PTEs released? and more importantly, > > > with or without holding the anon_vma_lock_write? > > > > I think you mean "pages" are still isolated and locked. I see the > > point. If the pages are unisolated before PMD is restored, the > > parallel try_to_unmap/migrate() may fail prematurely. > > > > Yes, I mean "pages". Therefore I think PMD re-establishing should > happen inside __collapse_huge_page_copy as one of the rollback > operations (and requiring passing @pmd and @rollback). Agree? Yeah, I didn't think of a better alternative to simply the code. If restoring PMD is handled outside of copy, the release_pte_page() should be called outside of copy too. I'm not sure if it is worth it or not. > > > > > > > > > + > > > > > + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR; > > > > > + _pte++, _address += PAGE_SIZE) { > > > > > + pteval = *_pte; > > > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > > > + if (copy_succeeded) { > > > > > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > > > + if (is_zero_pfn(pte_pfn(pteval))) { > > > > > + /* > > > > > + * ptl mostly unnecessary. > > > > > + */ > > > > > + spin_lock(pte_ptl); > > > > > + pte_clear(vma->vm_mm, _address, _pte); > > > > > + spin_unlock(pte_ptl); > > > > > + } > > > > > } > > > > > } else { > > > > > src_page = pte_page(pteval); > > > > > - copy_user_highpage(page, src_page, address, vma); > > > > > if (!PageCompound(src_page)) > > > > > release_pte_page(src_page); > > > > > - /* > > > > > - * ptl mostly unnecessary, but preempt has to > > > > > - * be disabled to update the per-cpu stats > > > > > - * inside page_remove_rmap(). > > > > > - */ > > > > > - spin_lock(ptl); > > > > > - ptep_clear(vma->vm_mm, address, _pte); > > > > > - page_remove_rmap(src_page, false); > > > > > - spin_unlock(ptl); > > > > > - free_page_and_swap_cache(src_page); > > > > > + > > > > > + if (copy_succeeded) { > > > > > + /* > > > > > + * ptl mostly unnecessary, but preempt has to > > > > > + * be disabled to update the per-cpu stats > > > > > + * inside page_remove_rmap(). > > > > > + */ > > > > > + spin_lock(pte_ptl); > > > > > + pte_clear(vma->vm_mm, _address, _pte); > > > > > + page_remove_rmap(src_page, false); > > > > > + spin_unlock(pte_ptl); > > > > > + free_page_and_swap_cache(src_page); > > > > > + } > > > > > } > > > > > } > > > > > > > > > > @@ -784,6 +839,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > > > list_del(&src_page->lru); > > > > > release_pte_page(src_page); > > > > > } > > > > > + > > > > > + return copy_succeeded; > > > > > } > > > > > > > > > > static void khugepaged_alloc_sleep(void) > > > > > @@ -1066,6 +1123,7 @@ static void collapse_huge_page(struct mm_struct *mm, > > > > > struct vm_area_struct *vma; > > > > > struct mmu_notifier_range range; > > > > > gfp_t gfp; > > > > > + bool copied = false; > > > > > > > > > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > > > > > > > > > @@ -1177,9 +1235,13 @@ static void collapse_huge_page(struct mm_struct *mm, > > > > > */ > > > > > anon_vma_unlock_write(vma->anon_vma); > > > > > > > > > > - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, > > > > > - &compound_pagelist); > > > > > + copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd, > > > > > + vma, address, pte_ptl, &compound_pagelist); > > > > > pte_unmap(pte); > > > > > + if (!copied) { > > > > > + result = SCAN_COPY_MC; > > > > > + goto out_up_write; > > > > > + } > > > > > /* > > > > > * spin_lock() below is not the equivalent of smp_wmb(), but > > > > > * the smp_wmb() inside __SetPageUptodate() can be reused to > > > > > @@ -1364,9 +1426,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > > > > > pte_unmap_unlock(pte, ptl); > > > > > if (ret) { > > > > > node = khugepaged_find_target_node(); > > > > > - /* collapse_huge_page will return with the mmap_lock released */ > > > > > - collapse_huge_page(mm, address, hpage, node, > > > > > - referenced, unmapped); > > > > > + /* > > > > > + * collapse_huge_page will return with the mmap_r+w_lock released. > > > > > + * It is uncertain if *hpage is NULL or not when collapse_huge_page > > > > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > > > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > > > > + * if collapse failed. > > > > > + */ > > > > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > > > > } > > > > > out: > > > > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > > > > @@ -2168,6 +2235,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > > > > > khugepaged_scan_file(mm, file, pgoff, hpage); > > > > > fput(file); > > > > > } else { > > > > > + /* > > > > > + * mmap_read_lock is > > > > > + * 1) released if both scan and collapse succeeded; > > > > > + * 2) still held if either scan or collapse failed. > > > > > > > > The #2 doesn't look correct. Even though collapse is failed, the > > > > mmap_lock is released as long as scan is succeeded. > > > > > > > > IIUC the collapse does: > > > > read unlock (passed in by scan) > > > > read lock > > > > read unlock > > > > write lock > > > > write unlock > > > > > > > > > > You are right! I will update this comment block in v3. > > > > > > > > + */ > > > > > ret = khugepaged_scan_pmd(mm, vma, > > > > > khugepaged_scan.address, > > > > > hpage); > > > > > -- > > > > > 2.35.1.1178.g4f1659d476-goog > > > > >
On Mon, May 23, 2022 at 2:13 PM Yang Shi <shy828301@gmail.com> wrote: > > On Mon, May 23, 2022 at 12:02 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > On Mon, May 23, 2022 at 11:48 AM Yang Shi <shy828301@gmail.com> wrote: > > > > > > On Fri, May 20, 2022 at 4:34 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > > > > > On Fri, Apr 29, 2022 at 3:15 PM Yang Shi <shy828301@gmail.com> wrote: > > > > > > > > > > On Thu, Apr 28, 2022 at 5:09 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > > > > > > > > > Make __collapse_huge_page_copy return whether > > > > > > collapsing/copying anonymous pages succeeded, > > > > > > and make collapse_huge_page handle the return status. > > > > > > > > > > > > Break existing PTE scan loop into two for-loops. > > > > > > The first loop copies source pages into target huge page, > > > > > > and can fail gracefully when running into memory errors in > > > > > > source pages. Roll back the page table and page states > > > > > > in the 2nd loop when copying failed: > > > > > > 1) re-establish the PTEs-to-PMD connection. > > > > > > 2) release pages back to their LRU list. > > > > > > > > > > Could you please include a changelog next time? It is really helpful > > > > > for reviewers. > > > > > > > > Of course, I will include change logs for both v2 + v3 changes. > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> > > > > > > --- > > > > > > include/linux/highmem.h | 19 ++++++ > > > > > > mm/khugepaged.c | 138 ++++++++++++++++++++++++++++++---------- > > > > > > 2 files changed, 124 insertions(+), 33 deletions(-) > > > > > > > > > > > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > > > > > > index 39bb9b47fa9cd..0ccb1e92c4b06 100644 > > > > > > --- a/include/linux/highmem.h > > > > > > +++ b/include/linux/highmem.h > > > > > > @@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from) > > > > > > > > > > > > #endif > > > > > > > > > > > > +/* > > > > > > + * Machine check exception handled version of copy_highpage. > > > > > > + * Return true if copying page content failed; otherwise false. > > > > > > + * Note handling #MC requires arch opt-in. > > > > > > + */ > > > > > > +static inline bool copy_highpage_mc(struct page *to, struct page *from) > > > > > > +{ > > > > > > + char *vfrom, *vto; > > > > > > + unsigned long ret; > > > > > > + > > > > > > + vfrom = kmap_local_page(from); > > > > > > + vto = kmap_local_page(to); > > > > > > + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE); > > > > > > + kunmap_local(vto); > > > > > > + kunmap_local(vfrom); > > > > > > + > > > > > > + return ret > 0; > > > > > > +} > > > > > > + > > > > > > static inline void memcpy_page(struct page *dst_page, size_t dst_off, > > > > > > struct page *src_page, size_t src_off, > > > > > > size_t len) > > > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > > > > index 131492fd1148b..8e69a0640e551 100644 > > > > > > --- a/mm/khugepaged.c > > > > > > +++ b/mm/khugepaged.c > > > > > > @@ -52,6 +52,7 @@ enum scan_result { > > > > > > SCAN_CGROUP_CHARGE_FAIL, > > > > > > SCAN_TRUNCATED, > > > > > > SCAN_PAGE_HAS_PRIVATE, > > > > > > + SCAN_COPY_MC, > > > > > > > > > > You need to update the tracepoint in > > > > > include/trace/events/huge_memory.h to include the new result. > > > > > > > > Will add tracepoint in v3. > > > > > > > > > > > > > > > }; > > > > > > > > > > > > #define CREATE_TRACE_POINTS > > > > > > @@ -739,44 +740,98 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > > > > > > return 0; > > > > > > } > > > > > > > > > > > > -static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > > > > - struct vm_area_struct *vma, > > > > > > - unsigned long address, > > > > > > - spinlock_t *ptl, > > > > > > - struct list_head *compound_pagelist) > > > > > > +/* > > > > > > > > > > Better to use "/**" so that it could be converted to kernel doc. > > > > > > > > Will update in v3. > > > > > > > > > > > > > > > + * __collapse_huge_page_copy - attempts to copy memory contents from normal > > > > > > + * pages to a hugepage. Cleanup the normal pages if copying succeeds; > > > > > > + * otherwise restore the original pmd page table. Returns true if copying > > > > > > + * succeeds, otherwise returns false. > > > > > > + * > > > > > > + * @pte: starting of the PTEs to copy from > > > > > > + * @page: the new hugepage to copy contents to > > > > > > + * @pmd: pointer to the new hugepage's PMD > > > > > > + * @rollback: the original normal PTEs' PMD > > > > > > > > > > You may not need pmd and rollback, please see the below comments for the reason. > > > > > > > > > > > + * @address: starting address to copy > > > > > > + * @pte_ptl: lock on normal pages' PTEs > > > > > > + * @compound_pagelist: list that stores compound pages > > > > > > + */ > > > > > > +static bool __collapse_huge_page_copy(pte_t *pte, > > > > > > + struct page *page, > > > > > > + pmd_t *pmd, > > > > > > + pmd_t rollback, > > > > > > + struct vm_area_struct *vma, > > > > > > + unsigned long address, > > > > > > + spinlock_t *pte_ptl, > > > > > > + struct list_head *compound_pagelist) > > > > > > { > > > > > > struct page *src_page, *tmp; > > > > > > pte_t *_pte; > > > > > > - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; > > > > > > - _pte++, page++, address += PAGE_SIZE) { > > > > > > - pte_t pteval = *_pte; > > > > > > + pte_t pteval; > > > > > > + unsigned long _address; > > > > > > + spinlock_t *pmd_ptl; > > > > > > + bool copy_succeeded = true; > > > > > > > > > > > > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > > > > + /* > > > > > > + * Copying pages' contents is subject to memory poison at any iteration. > > > > > > + */ > > > > > > + for (_pte = pte, _address = address; > > > > > > + _pte < pte + HPAGE_PMD_NR; > > > > > > + _pte++, page++, _address += PAGE_SIZE) { > > > > > > + pteval = *_pte; > > > > > > + > > > > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) > > > > > > clear_user_highpage(page, address); > > > > > > - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > > > > - if (is_zero_pfn(pte_pfn(pteval))) { > > > > > > - /* > > > > > > - * ptl mostly unnecessary. > > > > > > - */ > > > > > > - spin_lock(ptl); > > > > > > - ptep_clear(vma->vm_mm, address, _pte); > > > > > > - spin_unlock(ptl); > > > > > > + else { > > > > > > + src_page = pte_page(pteval); > > > > > > + if (copy_highpage_mc(page, src_page)) { > > > > > > + copy_succeeded = false; > > > > > > + break; > > > > > > + } > > > > > > + } > > > > > > + } > > > > > > + > > > > > > + if (!copy_succeeded) { > > > > > > + /* > > > > > > + * Copying failed, re-establish the regular PMD that > > > > > > + * points to regular page table. Since PTEs are still > > > > > > + * isolated and locked, acquiring anon_vma_lock is unnecessary. > > > > > > + */ > > > > > > + pmd_ptl = pmd_lock(vma->vm_mm, pmd); > > > > > > + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback)); > > > > > > + spin_unlock(pmd_ptl); > > > > > > + } > > > > > > > > > > I think the above section could be moved to out of > > > > > __collapse_huge_page_copy(), just like what is done after > > > > > __collapse_huge_page_isolate() is failed. > > > > > > > > > > You don't have to restore the pmd here since khugepaged holds write > > > > > mmap_lock, there can't be page fault running in parallel. Hence you > > > > > don't have to add pmd and rollback parameters to > > > > > __collapse_huge_page_copy(). > > > > > > > > > > > > > The reason I re-establish the pmd table here is to avoid anon_vma_lock_write > > > > since here PTEs are still isolated and locked. Are you implying that, we should > > > > do the PMD re-establishment after PTEs released? and more importantly, > > > > with or without holding the anon_vma_lock_write? > > > > > > I think you mean "pages" are still isolated and locked. I see the > > > point. If the pages are unisolated before PMD is restored, the > > > parallel try_to_unmap/migrate() may fail prematurely. > > > > > > > Yes, I mean "pages". Therefore I think PMD re-establishing should > > happen inside __collapse_huge_page_copy as one of the rollback > > operations (and requiring passing @pmd and @rollback). Agree? > > Yeah, I didn't think of a better alternative to simply the code. If > restoring PMD is handled outside of copy, the release_pte_page() > should be called outside of copy too. I'm not sure if it is worth it > or not. > Thanks, I will leave this part as it is, and send out V3 soon. > > > > > > > > > > > > + > > > > > > + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR; > > > > > > + _pte++, _address += PAGE_SIZE) { > > > > > > + pteval = *_pte; > > > > > > + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > > > > > > + if (copy_succeeded) { > > > > > > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > > > > > > + if (is_zero_pfn(pte_pfn(pteval))) { > > > > > > + /* > > > > > > + * ptl mostly unnecessary. > > > > > > + */ > > > > > > + spin_lock(pte_ptl); > > > > > > + pte_clear(vma->vm_mm, _address, _pte); > > > > > > + spin_unlock(pte_ptl); > > > > > > + } > > > > > > } > > > > > > } else { > > > > > > src_page = pte_page(pteval); > > > > > > - copy_user_highpage(page, src_page, address, vma); > > > > > > if (!PageCompound(src_page)) > > > > > > release_pte_page(src_page); > > > > > > - /* > > > > > > - * ptl mostly unnecessary, but preempt has to > > > > > > - * be disabled to update the per-cpu stats > > > > > > - * inside page_remove_rmap(). > > > > > > - */ > > > > > > - spin_lock(ptl); > > > > > > - ptep_clear(vma->vm_mm, address, _pte); > > > > > > - page_remove_rmap(src_page, false); > > > > > > - spin_unlock(ptl); > > > > > > - free_page_and_swap_cache(src_page); > > > > > > + > > > > > > + if (copy_succeeded) { > > > > > > + /* > > > > > > + * ptl mostly unnecessary, but preempt has to > > > > > > + * be disabled to update the per-cpu stats > > > > > > + * inside page_remove_rmap(). > > > > > > + */ > > > > > > + spin_lock(pte_ptl); > > > > > > + pte_clear(vma->vm_mm, _address, _pte); > > > > > > + page_remove_rmap(src_page, false); > > > > > > + spin_unlock(pte_ptl); > > > > > > + free_page_and_swap_cache(src_page); > > > > > > + } > > > > > > } > > > > > > } > > > > > > > > > > > > @@ -784,6 +839,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > > > > > > list_del(&src_page->lru); > > > > > > release_pte_page(src_page); > > > > > > } > > > > > > + > > > > > > + return copy_succeeded; > > > > > > } > > > > > > > > > > > > static void khugepaged_alloc_sleep(void) > > > > > > @@ -1066,6 +1123,7 @@ static void collapse_huge_page(struct mm_struct *mm, > > > > > > struct vm_area_struct *vma; > > > > > > struct mmu_notifier_range range; > > > > > > gfp_t gfp; > > > > > > + bool copied = false; > > > > > > > > > > > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > > > > > > > > > > > @@ -1177,9 +1235,13 @@ static void collapse_huge_page(struct mm_struct *mm, > > > > > > */ > > > > > > anon_vma_unlock_write(vma->anon_vma); > > > > > > > > > > > > - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, > > > > > > - &compound_pagelist); > > > > > > + copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd, > > > > > > + vma, address, pte_ptl, &compound_pagelist); > > > > > > pte_unmap(pte); > > > > > > + if (!copied) { > > > > > > + result = SCAN_COPY_MC; > > > > > > + goto out_up_write; > > > > > > + } > > > > > > /* > > > > > > * spin_lock() below is not the equivalent of smp_wmb(), but > > > > > > * the smp_wmb() inside __SetPageUptodate() can be reused to > > > > > > @@ -1364,9 +1426,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > > > > > > pte_unmap_unlock(pte, ptl); > > > > > > if (ret) { > > > > > > node = khugepaged_find_target_node(); > > > > > > - /* collapse_huge_page will return with the mmap_lock released */ > > > > > > - collapse_huge_page(mm, address, hpage, node, > > > > > > - referenced, unmapped); > > > > > > + /* > > > > > > + * collapse_huge_page will return with the mmap_r+w_lock released. > > > > > > + * It is uncertain if *hpage is NULL or not when collapse_huge_page > > > > > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > > > > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > > > > > + * if collapse failed. > > > > > > + */ > > > > > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > > > > > } > > > > > > out: > > > > > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > > > > > @@ -2168,6 +2235,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > > > > > > khugepaged_scan_file(mm, file, pgoff, hpage); > > > > > > fput(file); > > > > > > } else { > > > > > > + /* > > > > > > + * mmap_read_lock is > > > > > > + * 1) released if both scan and collapse succeeded; > > > > > > + * 2) still held if either scan or collapse failed. > > > > > > > > > > The #2 doesn't look correct. Even though collapse is failed, the > > > > > mmap_lock is released as long as scan is succeeded. > > > > > > > > > > IIUC the collapse does: > > > > > read unlock (passed in by scan) > > > > > read lock > > > > > read unlock > > > > > write lock > > > > > write unlock > > > > > > > > > > > > > You are right! I will update this comment block in v3. > > > > > > > > > > + */ > > > > > > ret = khugepaged_scan_pmd(mm, vma, > > > > > > khugepaged_scan.address, > > > > > > hpage); > > > > > > -- > > > > > > 2.35.1.1178.g4f1659d476-goog > > > > > >
diff --git a/include/linux/highmem.h b/include/linux/highmem.h index 39bb9b47fa9cd..0ccb1e92c4b06 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -298,6 +298,25 @@ static inline void copy_highpage(struct page *to, struct page *from) #endif +/* + * Machine check exception handled version of copy_highpage. + * Return true if copying page content failed; otherwise false. + * Note handling #MC requires arch opt-in. + */ +static inline bool copy_highpage_mc(struct page *to, struct page *from) +{ + char *vfrom, *vto; + unsigned long ret; + + vfrom = kmap_local_page(from); + vto = kmap_local_page(to); + ret = copy_mc_to_kernel(vto, vfrom, PAGE_SIZE); + kunmap_local(vto); + kunmap_local(vfrom); + + return ret > 0; +} + static inline void memcpy_page(struct page *dst_page, size_t dst_off, struct page *src_page, size_t src_off, size_t len) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 131492fd1148b..8e69a0640e551 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -52,6 +52,7 @@ enum scan_result { SCAN_CGROUP_CHARGE_FAIL, SCAN_TRUNCATED, SCAN_PAGE_HAS_PRIVATE, + SCAN_COPY_MC, }; #define CREATE_TRACE_POINTS @@ -739,44 +740,98 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, return 0; } -static void __collapse_huge_page_copy(pte_t *pte, struct page *page, - struct vm_area_struct *vma, - unsigned long address, - spinlock_t *ptl, - struct list_head *compound_pagelist) +/* + * __collapse_huge_page_copy - attempts to copy memory contents from normal + * pages to a hugepage. Cleanup the normal pages if copying succeeds; + * otherwise restore the original pmd page table. Returns true if copying + * succeeds, otherwise returns false. + * + * @pte: starting of the PTEs to copy from + * @page: the new hugepage to copy contents to + * @pmd: pointer to the new hugepage's PMD + * @rollback: the original normal PTEs' PMD + * @address: starting address to copy + * @pte_ptl: lock on normal pages' PTEs + * @compound_pagelist: list that stores compound pages + */ +static bool __collapse_huge_page_copy(pte_t *pte, + struct page *page, + pmd_t *pmd, + pmd_t rollback, + struct vm_area_struct *vma, + unsigned long address, + spinlock_t *pte_ptl, + struct list_head *compound_pagelist) { struct page *src_page, *tmp; pte_t *_pte; - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; - _pte++, page++, address += PAGE_SIZE) { - pte_t pteval = *_pte; + pte_t pteval; + unsigned long _address; + spinlock_t *pmd_ptl; + bool copy_succeeded = true; - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + /* + * Copying pages' contents is subject to memory poison at any iteration. + */ + for (_pte = pte, _address = address; + _pte < pte + HPAGE_PMD_NR; + _pte++, page++, _address += PAGE_SIZE) { + pteval = *_pte; + + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) clear_user_highpage(page, address); - add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); - if (is_zero_pfn(pte_pfn(pteval))) { - /* - * ptl mostly unnecessary. - */ - spin_lock(ptl); - ptep_clear(vma->vm_mm, address, _pte); - spin_unlock(ptl); + else { + src_page = pte_page(pteval); + if (copy_highpage_mc(page, src_page)) { + copy_succeeded = false; + break; + } + } + } + + if (!copy_succeeded) { + /* + * Copying failed, re-establish the regular PMD that + * points to regular page table. Since PTEs are still + * isolated and locked, acquiring anon_vma_lock is unnecessary. + */ + pmd_ptl = pmd_lock(vma->vm_mm, pmd); + pmd_populate(vma->vm_mm, pmd, pmd_pgtable(rollback)); + spin_unlock(pmd_ptl); + } + + for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR; + _pte++, _address += PAGE_SIZE) { + pteval = *_pte; + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + if (copy_succeeded) { + add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); + if (is_zero_pfn(pte_pfn(pteval))) { + /* + * ptl mostly unnecessary. + */ + spin_lock(pte_ptl); + pte_clear(vma->vm_mm, _address, _pte); + spin_unlock(pte_ptl); + } } } else { src_page = pte_page(pteval); - copy_user_highpage(page, src_page, address, vma); if (!PageCompound(src_page)) release_pte_page(src_page); - /* - * ptl mostly unnecessary, but preempt has to - * be disabled to update the per-cpu stats - * inside page_remove_rmap(). - */ - spin_lock(ptl); - ptep_clear(vma->vm_mm, address, _pte); - page_remove_rmap(src_page, false); - spin_unlock(ptl); - free_page_and_swap_cache(src_page); + + if (copy_succeeded) { + /* + * ptl mostly unnecessary, but preempt has to + * be disabled to update the per-cpu stats + * inside page_remove_rmap(). + */ + spin_lock(pte_ptl); + pte_clear(vma->vm_mm, _address, _pte); + page_remove_rmap(src_page, false); + spin_unlock(pte_ptl); + free_page_and_swap_cache(src_page); + } } } @@ -784,6 +839,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, list_del(&src_page->lru); release_pte_page(src_page); } + + return copy_succeeded; } static void khugepaged_alloc_sleep(void) @@ -1066,6 +1123,7 @@ static void collapse_huge_page(struct mm_struct *mm, struct vm_area_struct *vma; struct mmu_notifier_range range; gfp_t gfp; + bool copied = false; VM_BUG_ON(address & ~HPAGE_PMD_MASK); @@ -1177,9 +1235,13 @@ static void collapse_huge_page(struct mm_struct *mm, */ anon_vma_unlock_write(vma->anon_vma); - __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, - &compound_pagelist); + copied = __collapse_huge_page_copy(pte, new_page, pmd, _pmd, + vma, address, pte_ptl, &compound_pagelist); pte_unmap(pte); + if (!copied) { + result = SCAN_COPY_MC; + goto out_up_write; + } /* * spin_lock() below is not the equivalent of smp_wmb(), but * the smp_wmb() inside __SetPageUptodate() can be reused to @@ -1364,9 +1426,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, pte_unmap_unlock(pte, ptl); if (ret) { node = khugepaged_find_target_node(); - /* collapse_huge_page will return with the mmap_lock released */ - collapse_huge_page(mm, address, hpage, node, - referenced, unmapped); + /* + * collapse_huge_page will return with the mmap_r+w_lock released. + * It is uncertain if *hpage is NULL or not when collapse_huge_page + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock + * in khugepaged_scan_mm_slot, then *hpage will be freed + * if collapse failed. + */ + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); } out: trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, @@ -2168,6 +2235,11 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, khugepaged_scan_file(mm, file, pgoff, hpage); fput(file); } else { + /* + * mmap_read_lock is + * 1) released if both scan and collapse succeeded; + * 2) still held if either scan or collapse failed. + */ ret = khugepaged_scan_pmd(mm, vma, khugepaged_scan.address, hpage);
Make __collapse_huge_page_copy return whether collapsing/copying anonymous pages succeeded, and make collapse_huge_page handle the return status. Break existing PTE scan loop into two for-loops. The first loop copies source pages into target huge page, and can fail gracefully when running into memory errors in source pages. Roll back the page table and page states in the 2nd loop when copying failed: 1) re-establish the PTEs-to-PMD connection. 2) release pages back to their LRU list. Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> --- include/linux/highmem.h | 19 ++++++ mm/khugepaged.c | 138 ++++++++++++++++++++++++++++++---------- 2 files changed, 124 insertions(+), 33 deletions(-)