| Message ID | 20220524025352.1381911-2-jiaqiyan@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Memory poison recovery in khugepaged collapsing | expand |
On Mon, May 23, 2022 at 07:53:51PM -0700, Jiaqi Yan 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 > when copying failed: > 1) re-establish the PTEs-to-PMD connection. > 2) release pages back to their LRU list. If you spell out what the first loop does, just tell what the second loop does as wel, it just gets easier. > +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; > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > + src_page, SCAN_COPY_MC); You seem to assume that if there is an error, it will always happen on the page we are copying from. What if the page we are copying to is the fauly one? Can that happen? Can that be detected by copy_mc_to_kernel? And if so, can that be differentiated?
On Tue, May 24, 2022 at 3:48 AM Oscar Salvador <osalvador@suse.de> wrote: > > On Mon, May 23, 2022 at 07:53:51PM -0700, Jiaqi Yan 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 > > when copying failed: > > 1) re-establish the PTEs-to-PMD connection. > > 2) release pages back to their LRU list. > > If you spell out what the first loop does, just tell > what the second loop does as wel, it just gets easier. > > > +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; > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > + src_page, SCAN_COPY_MC); > > You seem to assume that if there is an error, it will always happen on > the page we are copying from. What if the page we are copying to is the > fauly one? Can that happen? Can that be detected by copy_mc_to_kernel? > And if so, can that be differentiated? It's possible that the copy to page has some uncorrectable memory errors. Yet only read transactions signals machine check exceptions while write transactions do not. It's the reading from the source page with uncorrectable errors causing system panics most (since khugepaged is a kernel context thread). Thanks, -Jue > > -- > Oscar Salvador > SUSE Labs
On Tue, May 24, 2022 at 7:05 AM Jue Wang <juew@google.com> wrote: > > On Tue, May 24, 2022 at 3:48 AM Oscar Salvador <osalvador@suse.de> wrote: > > > > On Mon, May 23, 2022 at 07:53:51PM -0700, Jiaqi Yan 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 > > > when copying failed: > > > 1) re-establish the PTEs-to-PMD connection. > > > 2) release pages back to their LRU list. > > > > If you spell out what the first loop does, just tell > > what the second loop does as wel, it just gets easier. > > Thanks for the suggestion. I will amend the commit msg in the next version as follows: If copying all pages succeeds, the second loop releases and clears up these normal pages. Otherwise, the second loop does the followings to roll back the page table and page states: 1) re-establish the original PTEs-to-PMD connection. 2) release source pages back to their LRU list. > > > > +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; > > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > > + src_page, SCAN_COPY_MC); > > > > You seem to assume that if there is an error, it will always happen on > > the page we are copying from. What if the page we are copying to is the > > fauly one? Can that happen? Can that be detected by copy_mc_to_kernel? > > And if so, can that be differentiated? > It's possible that the copy to page has some uncorrectable memory errors. > > Yet only read transactions signals machine check exceptions while > write transactions do not. > > It's the reading from the source page with uncorrectable errors > causing system panics most (since khugepaged is a kernel context > thread). > > > Thanks, > -Jue > > > > -- > > Oscar Salvador > > SUSE Labs
On Mon, May 23, 2022 at 7:54 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 > 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 ++++ > include/trace/events/huge_memory.h | 27 +++++- > mm/khugepaged.c | 146 ++++++++++++++++++++++------- > 3 files changed, 158 insertions(+), 34 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/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > index 4fdb14a81108b..7e02c0aa2f728 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -34,7 +34,8 @@ > EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ > EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ > EM( SCAN_TRUNCATED, "truncated") \ > - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > + EMe(SCAN_COPY_MC, "copy_poisoned_page") \ > > #undef EM > #undef EMe > @@ -167,5 +168,29 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, > __entry->ret) > ); > > +TRACE_EVENT(mm_collapse_huge_page_copy, You may misunderstand my point. I don't mean we need a new tracepoint, IMHO trace_mm_collapse_huge_page() is good enough. When copy is failed you do have "result = SCAN_COPY_MC" and the result will be consumed by trace_mm_collapse_huge_page(). You just need have trace interpret the new result as the above section does. > + > + TP_PROTO(struct page *start, struct page *poisoned, int status), > + > + TP_ARGS(start, poisoned, status), > + > + TP_STRUCT__entry( > + __field(unsigned long, start_pfn) > + __field(unsigned long, poisoned_pfn) > + __field(int, status) > + ), > + > + TP_fast_assign( > + __entry->start_pfn = start ? page_to_pfn(start) : -1; > + __entry->poisoned_pfn = poisoned ? page_to_pfn(poisoned) : -1; > + __entry->status = status; > + ), > + > + TP_printk("start_pfn=0x%lx, poisoned_pfn=0x%lx, status=%s", > + __entry->start_pfn, > + __entry->poisoned_pfn, > + __print_symbolic(__entry->status, SCAN_STATUS)) > +); > + > #endif /* __HUGE_MEMORY_H */ > #include <trace/define_trace.h> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 131492fd1148b..1b08e31ba081a 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 +740,104 @@ 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 page table and release isolated normal pages. > + * 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 orginal normal pages' PMD s/orginal/original > + * @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; > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > + src_page, SCAN_COPY_MC); As aforementioned I don't think we need a new trace point. > + break; > + } > + } > + } > + > + if (copy_succeeded) > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > + NULL, SCAN_SUCCEED); > + else { > + /* > + * Copying failed, re-establish the regular PMD that points to > + * the regular page table. Restoring PMD needs to be done prior > + * to releasing pages. Since pages are still isolated and locked > + * here, acquiring anon_vma_lock_write 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 +845,8 @@ 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 +1129,7 @@ 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 +1241,13 @@ 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 +1432,14 @@ 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 Why is it uncertain? > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock "ret=1" means scan succeeded so mmap_lock is released. But this happens in the caller. > + * in khugepaged_scan_mm_slot, then *hpage will be freed > + * if collapse failed. It depends. For CONFIG_NUMA, it will be freed since next scan may need a page from a different node, but !CONFIG_NUMA may not free it, it may be reused IIUC. We do intend to remove this optimization, but it has not happened yet. TBH I don't think the comment is helpful here and actually confusing, I'd prefer to have it right before calling khugepaged_scan_pmd() if you would like to keep it. > + */ > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > } > out: > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > @@ -2168,6 +2241,13 @@ 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) still held if scan failed; > + * 2) released if scan succeeded. > + * It is not affected by collapsing or copying > + * operations. > + */ > ret = khugepaged_scan_pmd(mm, vma, > khugepaged_scan.address, > hpage); > -- > 2.36.1.124.g0e6072fb45-goog >
On Tue, May 24, 2022 at 11:41 AM Yang Shi <shy828301@gmail.com> wrote: > > On Mon, May 23, 2022 at 7:54 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 > > 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 ++++ > > include/trace/events/huge_memory.h | 27 +++++- > > mm/khugepaged.c | 146 ++++++++++++++++++++++------- > > 3 files changed, 158 insertions(+), 34 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/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > > index 4fdb14a81108b..7e02c0aa2f728 100644 > > --- a/include/trace/events/huge_memory.h > > +++ b/include/trace/events/huge_memory.h > > @@ -34,7 +34,8 @@ > > EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ > > EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ > > EM( SCAN_TRUNCATED, "truncated") \ > > - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > > + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > > + EMe(SCAN_COPY_MC, "copy_poisoned_page") \ > > > > #undef EM > > #undef EMe > > @@ -167,5 +168,29 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, > > __entry->ret) > > ); > > > > +TRACE_EVENT(mm_collapse_huge_page_copy, > > You may misunderstand my point. I don't mean we need a new tracepoint, > IMHO trace_mm_collapse_huge_page() is good enough. When copy is failed > you do have "result = SCAN_COPY_MC" and the result will be consumed by > trace_mm_collapse_huge_page(). You just need have trace interpret the > new result as the above section does. I see. To make sure we are on the same page, I think we only need to add: EMe(SCAN_COPY_MC, "copy_poisoned_page") I don't think we need to add a 'copied' arg in mm_collapse_huge_page() as "copy_poisoned_page" is the only reason copied=false. My intention to add a new tracepoint is for showing the poisoned PFN but I feel you don't think this is very important information w.r.t khugepaged. The important thing is we skipped the poisoned page(s). > > > + > > + TP_PROTO(struct page *start, struct page *poisoned, int status), > > + > > + TP_ARGS(start, poisoned, status), > > + > > + TP_STRUCT__entry( > > + __field(unsigned long, start_pfn) > > + __field(unsigned long, poisoned_pfn) > > + __field(int, status) > > + ), > > + > > + TP_fast_assign( > > + __entry->start_pfn = start ? page_to_pfn(start) : -1; > > + __entry->poisoned_pfn = poisoned ? page_to_pfn(poisoned) : -1; > > + __entry->status = status; > > + ), > > + > > + TP_printk("start_pfn=0x%lx, poisoned_pfn=0x%lx, status=%s", > > + __entry->start_pfn, > > + __entry->poisoned_pfn, > > + __print_symbolic(__entry->status, SCAN_STATUS)) > > +); > > + > > #endif /* __HUGE_MEMORY_H */ > > #include <trace/define_trace.h> > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 131492fd1148b..1b08e31ba081a 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 +740,104 @@ 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 page table and release isolated normal pages. > > + * 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 orginal normal pages' PMD > > s/orginal/original > > > + * @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; > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > + src_page, SCAN_COPY_MC); > > As aforementioned I don't think we need a new trace point. > > > + break; > > + } > > + } > > + } > > + > > + if (copy_succeeded) > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > + NULL, SCAN_SUCCEED); > > + else { > > + /* > > + * Copying failed, re-establish the regular PMD that points to > > + * the regular page table. Restoring PMD needs to be done prior > > + * to releasing pages. Since pages are still isolated and locked > > + * here, acquiring anon_vma_lock_write 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 +845,8 @@ 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 +1129,7 @@ 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 +1241,13 @@ 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 +1432,14 @@ 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 > > Why is it uncertain? By "uncertain" I mean *hpage may not be set to NULL near the end of collapse_huge_page if swapin/isolation/copying failed. > > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > "ret=1" means scan succeeded so mmap_lock is released. But this > happens in the caller. > > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > + * if collapse failed. > > It depends. For CONFIG_NUMA, it will be freed since next scan may need > a page from a different node, but !CONFIG_NUMA may not free it, it may > be reused IIUC. We do intend to remove this optimization, but it has > not happened yet. Yes, you are right if !CONFIG_NUMA, khugepaged_prealloc_page only free *hpage when page_count(*hpage) > 1. > > TBH I don't think the comment is helpful here and actually confusing, > I'd prefer to have it right before calling khugepaged_scan_pmd() if > you would like to keep it. I will remove the comment and revert this part. > > > + */ > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > } > > out: > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > @@ -2168,6 +2241,13 @@ 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) still held if scan failed; > > + * 2) released if scan succeeded. > > + * It is not affected by collapsing or copying > > + * operations. > > + */ > > ret = khugepaged_scan_pmd(mm, vma, > > khugepaged_scan.address, > > hpage); > > -- > > 2.36.1.124.g0e6072fb45-goog > >
On Thu, May 26, 2022 at 5:06 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > On Tue, May 24, 2022 at 11:41 AM Yang Shi <shy828301@gmail.com> wrote: > > > > On Mon, May 23, 2022 at 7:54 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 > > > 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 ++++ > > > include/trace/events/huge_memory.h | 27 +++++- > > > mm/khugepaged.c | 146 ++++++++++++++++++++++------- > > > 3 files changed, 158 insertions(+), 34 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/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > > > index 4fdb14a81108b..7e02c0aa2f728 100644 > > > --- a/include/trace/events/huge_memory.h > > > +++ b/include/trace/events/huge_memory.h > > > @@ -34,7 +34,8 @@ > > > EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ > > > EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ > > > EM( SCAN_TRUNCATED, "truncated") \ > > > - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > > > + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > > > + EMe(SCAN_COPY_MC, "copy_poisoned_page") \ > > > > > > #undef EM > > > #undef EMe > > > @@ -167,5 +168,29 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, > > > __entry->ret) > > > ); > > > > > > +TRACE_EVENT(mm_collapse_huge_page_copy, > > > > You may misunderstand my point. I don't mean we need a new tracepoint, > > IMHO trace_mm_collapse_huge_page() is good enough. When copy is failed > > you do have "result = SCAN_COPY_MC" and the result will be consumed by > > trace_mm_collapse_huge_page(). You just need have trace interpret the > > new result as the above section does. > > I see. To make sure we are on the same page, I think we only need to add: > > EMe(SCAN_COPY_MC, "copy_poisoned_page") Yes > > I don't think we need to add a 'copied' arg in mm_collapse_huge_page() as > "copy_poisoned_page" is the only reason copied=false. > > My intention to add a new tracepoint is for showing the poisoned PFN but I feel > you don't think this is very important information w.r.t khugepaged. > The important > thing is we skipped the poisoned page(s). I think memory failure will report the detailed information later. Khugepaged just needs to know the reason IMHO. > > > > > > + > > > + TP_PROTO(struct page *start, struct page *poisoned, int status), > > > + > > > + TP_ARGS(start, poisoned, status), > > > + > > > + TP_STRUCT__entry( > > > + __field(unsigned long, start_pfn) > > > + __field(unsigned long, poisoned_pfn) > > > + __field(int, status) > > > + ), > > > + > > > + TP_fast_assign( > > > + __entry->start_pfn = start ? page_to_pfn(start) : -1; > > > + __entry->poisoned_pfn = poisoned ? page_to_pfn(poisoned) : -1; > > > + __entry->status = status; > > > + ), > > > + > > > + TP_printk("start_pfn=0x%lx, poisoned_pfn=0x%lx, status=%s", > > > + __entry->start_pfn, > > > + __entry->poisoned_pfn, > > > + __print_symbolic(__entry->status, SCAN_STATUS)) > > > +); > > > + > > > #endif /* __HUGE_MEMORY_H */ > > > #include <trace/define_trace.h> > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > index 131492fd1148b..1b08e31ba081a 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 +740,104 @@ 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 page table and release isolated normal pages. > > > + * 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 orginal normal pages' PMD > > > > s/orginal/original > > > > > + * @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; > > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > > + src_page, SCAN_COPY_MC); > > > > As aforementioned I don't think we need a new trace point. > > > > > + break; > > > + } > > > + } > > > + } > > > + > > > + if (copy_succeeded) > > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > > + NULL, SCAN_SUCCEED); > > > + else { > > > + /* > > > + * Copying failed, re-establish the regular PMD that points to > > > + * the regular page table. Restoring PMD needs to be done prior > > > + * to releasing pages. Since pages are still isolated and locked > > > + * here, acquiring anon_vma_lock_write 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 +845,8 @@ 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 +1129,7 @@ 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 +1241,13 @@ 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 +1432,14 @@ 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 > > > > Why is it uncertain? > > By "uncertain" I mean *hpage may not be set to NULL near the end of > collapse_huge_page > if swapin/isolation/copying failed. > > > > > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > > > "ret=1" means scan succeeded so mmap_lock is released. But this > > happens in the caller. > > > > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > > + * if collapse failed. > > > > It depends. For CONFIG_NUMA, it will be freed since next scan may need > > a page from a different node, but !CONFIG_NUMA may not free it, it may > > be reused IIUC. We do intend to remove this optimization, but it has > > not happened yet. > > Yes, you are right if !CONFIG_NUMA, khugepaged_prealloc_page only > free *hpage when page_count(*hpage) > 1. > > > > > TBH I don't think the comment is helpful here and actually confusing, > > I'd prefer to have it right before calling khugepaged_scan_pmd() if > > you would like to keep it. > > I will remove the comment and revert this part. > > > > > > + */ > > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > > } > > > out: > > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > > @@ -2168,6 +2241,13 @@ 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) still held if scan failed; > > > + * 2) released if scan succeeded. > > > + * It is not affected by collapsing or copying > > > + * operations. > > > + */ > > > ret = khugepaged_scan_pmd(mm, vma, > > > khugepaged_scan.address, > > > hpage); > > > -- > > > 2.36.1.124.g0e6072fb45-goog > > >
On Fri, May 27, 2022 at 8:42 AM Yang Shi <shy828301@gmail.com> wrote: > > On Thu, May 26, 2022 at 5:06 PM Jiaqi Yan <jiaqiyan@google.com> wrote: > > > > On Tue, May 24, 2022 at 11:41 AM Yang Shi <shy828301@gmail.com> wrote: > > > > > > On Mon, May 23, 2022 at 7:54 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 > > > > 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 ++++ > > > > include/trace/events/huge_memory.h | 27 +++++- > > > > mm/khugepaged.c | 146 ++++++++++++++++++++++------- > > > > 3 files changed, 158 insertions(+), 34 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/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > > > > index 4fdb14a81108b..7e02c0aa2f728 100644 > > > > --- a/include/trace/events/huge_memory.h > > > > +++ b/include/trace/events/huge_memory.h > > > > @@ -34,7 +34,8 @@ > > > > EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ > > > > EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ > > > > EM( SCAN_TRUNCATED, "truncated") \ > > > > - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > > > > + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > > > > + EMe(SCAN_COPY_MC, "copy_poisoned_page") \ > > > > > > > > #undef EM > > > > #undef EMe > > > > @@ -167,5 +168,29 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, > > > > __entry->ret) > > > > ); > > > > > > > > +TRACE_EVENT(mm_collapse_huge_page_copy, > > > > > > You may misunderstand my point. I don't mean we need a new tracepoint, > > > IMHO trace_mm_collapse_huge_page() is good enough. When copy is failed > > > you do have "result = SCAN_COPY_MC" and the result will be consumed by > > > trace_mm_collapse_huge_page(). You just need have trace interpret the > > > new result as the above section does. > > > > I see. To make sure we are on the same page, I think we only need to add: > > > > EMe(SCAN_COPY_MC, "copy_poisoned_page") > > Yes > > > > > I don't think we need to add a 'copied' arg in mm_collapse_huge_page() as > > "copy_poisoned_page" is the only reason copied=false. > > > > My intention to add a new tracepoint is for showing the poisoned PFN but I feel > > you don't think this is very important information w.r.t khugepaged. > > The important > > thing is we skipped the poisoned page(s). > > I think memory failure will report the detailed information later. > Khugepaged just needs to know the reason IMHO. > Eventually yes. For example if userspace accesses the memory error, then memory_failure() will be invoked in the MCE handling code path. A future workitem could be to make the memory_failure() happen right away in the khugepaged context. But for now I don't have a very good concrete scenario to demonstrate that doing this is better than wait memory_failure() happening later. Anyway, this is not intended to be included in this patch series. I will send out v4 asap. > > > > > > > > > + > > > > + TP_PROTO(struct page *start, struct page *poisoned, int status), > > > > + > > > > + TP_ARGS(start, poisoned, status), > > > > + > > > > + TP_STRUCT__entry( > > > > + __field(unsigned long, start_pfn) > > > > + __field(unsigned long, poisoned_pfn) > > > > + __field(int, status) > > > > + ), > > > > + > > > > + TP_fast_assign( > > > > + __entry->start_pfn = start ? page_to_pfn(start) : -1; > > > > + __entry->poisoned_pfn = poisoned ? page_to_pfn(poisoned) : -1; > > > > + __entry->status = status; > > > > + ), > > > > + > > > > + TP_printk("start_pfn=0x%lx, poisoned_pfn=0x%lx, status=%s", > > > > + __entry->start_pfn, > > > > + __entry->poisoned_pfn, > > > > + __print_symbolic(__entry->status, SCAN_STATUS)) > > > > +); > > > > + > > > > #endif /* __HUGE_MEMORY_H */ > > > > #include <trace/define_trace.h> > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > > > index 131492fd1148b..1b08e31ba081a 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 +740,104 @@ 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 page table and release isolated normal pages. > > > > + * 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 orginal normal pages' PMD > > > > > > s/orginal/original > > > > > > > + * @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; > > > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > > > + src_page, SCAN_COPY_MC); > > > > > > As aforementioned I don't think we need a new trace point. > > > > > > > + break; > > > > + } > > > > + } > > > > + } > > > > + > > > > + if (copy_succeeded) > > > > + trace_mm_collapse_huge_page_copy(pte_page(*pte), > > > > + NULL, SCAN_SUCCEED); > > > > + else { > > > > + /* > > > > + * Copying failed, re-establish the regular PMD that points to > > > > + * the regular page table. Restoring PMD needs to be done prior > > > > + * to releasing pages. Since pages are still isolated and locked > > > > + * here, acquiring anon_vma_lock_write 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 +845,8 @@ 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 +1129,7 @@ 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 +1241,13 @@ 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 +1432,14 @@ 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 > > > > > > Why is it uncertain? > > > > By "uncertain" I mean *hpage may not be set to NULL near the end of > > collapse_huge_page > > if swapin/isolation/copying failed. > > > > > > > > > + * returns, so keep ret=1 to jump to breakouterloop_mmap_lock > > > > > > "ret=1" means scan succeeded so mmap_lock is released. But this > > > happens in the caller. > > > > > > > + * in khugepaged_scan_mm_slot, then *hpage will be freed > > > > + * if collapse failed. > > > > > > It depends. For CONFIG_NUMA, it will be freed since next scan may need > > > a page from a different node, but !CONFIG_NUMA may not free it, it may > > > be reused IIUC. We do intend to remove this optimization, but it has > > > not happened yet. > > > > Yes, you are right if !CONFIG_NUMA, khugepaged_prealloc_page only > > free *hpage when page_count(*hpage) > 1. > > > > > > > > TBH I don't think the comment is helpful here and actually confusing, > > > I'd prefer to have it right before calling khugepaged_scan_pmd() if > > > you would like to keep it. > > > > I will remove the comment and revert this part. > > > > > > > > > + */ > > > > + collapse_huge_page(mm, address, hpage, node, referenced, unmapped); > > > > } > > > > out: > > > > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, > > > > @@ -2168,6 +2241,13 @@ 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) still held if scan failed; > > > > + * 2) released if scan succeeded. > > > > + * It is not affected by collapsing or copying > > > > + * operations. > > > > + */ > > > > ret = khugepaged_scan_pmd(mm, vma, > > > > khugepaged_scan.address, > > > > hpage); > > > > -- > > > > 2.36.1.124.g0e6072fb45-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/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 4fdb14a81108b..7e02c0aa2f728 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -34,7 +34,8 @@ EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ EM( SCAN_TRUNCATED, "truncated") \ - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ + EMe(SCAN_COPY_MC, "copy_poisoned_page") \ #undef EM #undef EMe @@ -167,5 +168,29 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, __entry->ret) ); +TRACE_EVENT(mm_collapse_huge_page_copy, + + TP_PROTO(struct page *start, struct page *poisoned, int status), + + TP_ARGS(start, poisoned, status), + + TP_STRUCT__entry( + __field(unsigned long, start_pfn) + __field(unsigned long, poisoned_pfn) + __field(int, status) + ), + + TP_fast_assign( + __entry->start_pfn = start ? page_to_pfn(start) : -1; + __entry->poisoned_pfn = poisoned ? page_to_pfn(poisoned) : -1; + __entry->status = status; + ), + + TP_printk("start_pfn=0x%lx, poisoned_pfn=0x%lx, status=%s", + __entry->start_pfn, + __entry->poisoned_pfn, + __print_symbolic(__entry->status, SCAN_STATUS)) +); + #endif /* __HUGE_MEMORY_H */ #include <trace/define_trace.h> diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 131492fd1148b..1b08e31ba081a 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 +740,104 @@ 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 page table and release isolated normal pages. + * 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 orginal normal pages' 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; + trace_mm_collapse_huge_page_copy(pte_page(*pte), + src_page, SCAN_COPY_MC); + break; + } + } + } + + if (copy_succeeded) + trace_mm_collapse_huge_page_copy(pte_page(*pte), + NULL, SCAN_SUCCEED); + else { + /* + * Copying failed, re-establish the regular PMD that points to + * the regular page table. Restoring PMD needs to be done prior + * to releasing pages. Since pages are still isolated and locked + * here, acquiring anon_vma_lock_write 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 +845,8 @@ 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 +1129,7 @@ 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 +1241,13 @@ 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 +1432,14 @@ 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 +2241,13 @@ 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) still held if scan failed; + * 2) released if scan succeeded. + * It is not affected by collapsing or copying + * operations. + */ 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 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 ++++ include/trace/events/huge_memory.h | 27 +++++- mm/khugepaged.c | 146 ++++++++++++++++++++++------- 3 files changed, 158 insertions(+), 34 deletions(-)