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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2020-06-03 16:00:09 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-03 20:09:46 -0700
commitffe945e633b527d5a4577b42cbadec3c7cbcf096 (patch)
treeea7bb830b6d625cf4981465639ca3a1fc2269773 /mm/khugepaged.c
parente0c13f9761df8f97cf5e81495d12ecbc4075684a (diff)
khugepaged: do not stop collapse if less than half PTEs are 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. Fixes: 0db501f7a34c ("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>
Diffstat (limited to 'mm/khugepaged.c')
-rw-r--r--mm/khugepaged.c27
1 files changed, 11 insertions, 16 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index cd280afb246e..c436fd390296 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -899,11 +899,6 @@ 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) {
@@ -943,7 +938,7 @@ 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;
@@ -1000,7 +995,8 @@ 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;
@@ -1233,22 +1229,21 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
mmu_notifier_test_young(vma->vm_mm, address))
referenced++;
}
- if (writable) {
- if (referenced) {
- result = SCAN_SUCCEED;
- ret = 1;
- } else {
- result = SCAN_LACK_REFERENCED_PAGE;
- }
- } else {
+ 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;
}
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,