| Message ID | 20200413125220.663-3-kirill.shutemov@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | thp/khugepaged improvements and CoW semantics | expand |
On 4/13/20 5:52 AM, Kirill A. Shutemov wrote: > __collapse_huge_page_swapin() checks the number of referenced PTE to > decide if the memory range is hot enough to justify swapin. > > We have few problems with the approach: > > - It is way too late: we can do the check much earlier and safe time. > khugepaged_scan_pmd() already knows if we have any pages to swap in > and number of referenced page. > > - It stops collapse altogether if there's not enough referenced pages, > not only swappingin. > > Fix it by making the right check early. We also can avoid additional > page table scanning if khugepaged_scan_pmd() haven't found any swap > entries. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsing to conservative") > --- > mm/khugepaged.c | 25 ++++++++++--------------- > 1 file changed, 10 insertions(+), 15 deletions(-) Acked-by: Yang Shi <yang.shi@linux.alibaba.com> Just a nit below. > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 99bab7e4d05b..5968ec5ddd6b 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -902,11 +902,6 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, > .pgoff = linear_page_index(vma, address), > }; > > - /* we only decide to swapin, if there is enough young ptes */ > - if (referenced < HPAGE_PMD_NR/2) { > - trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); > - return false; > - } > vmf.pte = pte_offset_map(pmd, address); > for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE; > vmf.pte++, vmf.address += PAGE_SIZE) { > @@ -946,7 +941,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, > static void collapse_huge_page(struct mm_struct *mm, > unsigned long address, > struct page **hpage, > - int node, int referenced) > + int node, int referenced, int unmapped) > { > pmd_t *pmd, _pmd; > pte_t *pte; > @@ -1003,7 +998,8 @@ static void collapse_huge_page(struct mm_struct *mm, > * If it fails, we release mmap_sem and jump out_nolock. > * Continuing to collapse causes inconsistency. > */ > - if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) { > + if (unmapped && !__collapse_huge_page_swapin(mm, vma, address, > + pmd, referenced)) { > mem_cgroup_cancel_charge(new_page, memcg, true); > up_read(&mm->mmap_sem); > goto out_nolock; > @@ -1214,22 +1210,21 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > mmu_notifier_test_young(vma->vm_mm, address)) > referenced++; > } > - if (writable) { > - if (referenced) { > + if (!writable) { > + result = SCAN_PAGE_RO; > + } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) { > + result = SCAN_LACK_REFERENCED_PAGE; > + } else { > result = SCAN_SUCCEED; > ret = 1; Shall fix the indentation for the above two statements? > - } else { > - result = SCAN_LACK_REFERENCED_PAGE; > - } > - } else { > - result = SCAN_PAGE_RO; > } > out_unmap: > pte_unmap_unlock(pte, ptl); > if (ret) { > node = khugepaged_find_target_node(); > /* collapse_huge_page will return with the mmap_sem released */ > - collapse_huge_page(mm, address, hpage, node, referenced); > + collapse_huge_page(mm, address, hpage, node, > + referenced, unmapped); > } > out: > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 99bab7e4d05b..5968ec5ddd6b 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -902,11 +902,6 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, .pgoff = linear_page_index(vma, address), }; - /* we only decide to swapin, if there is enough young ptes */ - if (referenced < HPAGE_PMD_NR/2) { - trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); - return false; - } vmf.pte = pte_offset_map(pmd, address); for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE; vmf.pte++, vmf.address += PAGE_SIZE) { @@ -946,7 +941,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, static void collapse_huge_page(struct mm_struct *mm, unsigned long address, struct page **hpage, - int node, int referenced) + int node, int referenced, int unmapped) { pmd_t *pmd, _pmd; pte_t *pte; @@ -1003,7 +998,8 @@ static void collapse_huge_page(struct mm_struct *mm, * If it fails, we release mmap_sem and jump out_nolock. * Continuing to collapse causes inconsistency. */ - if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) { + if (unmapped && !__collapse_huge_page_swapin(mm, vma, address, + pmd, referenced)) { mem_cgroup_cancel_charge(new_page, memcg, true); up_read(&mm->mmap_sem); goto out_nolock; @@ -1214,22 +1210,21 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, mmu_notifier_test_young(vma->vm_mm, address)) referenced++; } - if (writable) { - if (referenced) { + if (!writable) { + result = SCAN_PAGE_RO; + } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) { + result = SCAN_LACK_REFERENCED_PAGE; + } else { result = SCAN_SUCCEED; ret = 1; - } else { - result = SCAN_LACK_REFERENCED_PAGE; - } - } else { - result = SCAN_PAGE_RO; } out_unmap: pte_unmap_unlock(pte, ptl); if (ret) { node = khugepaged_find_target_node(); /* collapse_huge_page will return with the mmap_sem released */ - collapse_huge_page(mm, address, hpage, node, referenced); + collapse_huge_page(mm, address, hpage, node, + referenced, unmapped); } out: trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
__collapse_huge_page_swapin() checks the number of referenced PTE to decide if the memory range is hot enough to justify swapin. We have few problems with the approach: - It is way too late: we can do the check much earlier and safe time. khugepaged_scan_pmd() already knows if we have any pages to swap in and number of referenced page. - It stops collapse altogether if there's not enough referenced pages, not only swappingin. Fix it by making the right check early. We also can avoid additional page table scanning if khugepaged_scan_pmd() haven't found any swap entries. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsing to conservative") --- mm/khugepaged.c | 25 ++++++++++--------------- 1 file changed, 10 insertions(+), 15 deletions(-)