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khugepaged: do not stop collapse if less than half PTEs are referenced

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__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.

Fixes: 0db501f7a3 ("mm, thp: convert from optimistic swapin collapsing to conservative")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Link: http://lkml.kernel.org/r/20200416160026.16538-3-kirill.shutemov@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2020-06-03 16:00:09 -07:00 committed by Linus Torvalds
parent e0c13f9761
commit ffe945e633
1 changed files with 11 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
mm/khugepaged.c
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@ -899,11 +899,6 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
.pgoff = linear_page_index(vma, address), .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); vmf.pte = pte_offset_map(pmd, address);
for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE; for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
vmf.pte++, vmf.address += PAGE_SIZE) { vmf.pte++, vmf.address += PAGE_SIZE) {
@ -943,7 +938,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
static void collapse_huge_page(struct mm_struct *mm, static void collapse_huge_page(struct mm_struct *mm,
unsigned long address, unsigned long address,
struct page **hpage, struct page **hpage,
int node, int referenced) int node, int referenced, int unmapped)
{ {
pmd_t *pmd, _pmd; pmd_t *pmd, _pmd;
pte_t *pte; pte_t *pte;
@ -1000,7 +995,8 @@ static void collapse_huge_page(struct mm_struct *mm,
* If it fails, we release mmap_sem and jump out_nolock. * If it fails, we release mmap_sem and jump out_nolock.
* Continuing to collapse causes inconsistency. * 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); mem_cgroup_cancel_charge(new_page, memcg, true);
up_read(&mm->mmap_sem); up_read(&mm->mmap_sem);
goto out_nolock; goto out_nolock;
@ -1233,22 +1229,21 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
mmu_notifier_test_young(vma->vm_mm, address)) mmu_notifier_test_young(vma->vm_mm, address))
referenced++; referenced++;
} }
if (writable) { if (!writable) {
if (referenced) {
result = SCAN_SUCCEED;
ret = 1;
} else {
result = SCAN_LACK_REFERENCED_PAGE;
}
} else {
result = SCAN_PAGE_RO; result = SCAN_PAGE_RO;
} else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
ret = 1;
} }
out_unmap: out_unmap:
pte_unmap_unlock(pte, ptl); pte_unmap_unlock(pte, ptl);
if (ret) { if (ret) {
node = khugepaged_find_target_node(); node = khugepaged_find_target_node();
/* collapse_huge_page will return with the mmap_sem released */ /* 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: out:
trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,