From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: akpm@linux-foundation.org, Andrea Arcangeli <aarcange@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>, Yang Shi <yang.shi@linux.alibaba.com>,
Ralph Campbell <rcampbell@nvidia.com>,
John Hubbard <jhubbard@nvidia.com>,
William Kucharski <william.kucharski@oracle.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCHv4 2/8] khugepaged: Do not stop collapse if less than half PTEs are referenced
Date: Thu, 16 Apr 2020 19:00:20 +0300 [thread overview]
Message-ID: <20200416160026.16538-3-kirill.shutemov@linux.intel.com> (raw)
In-Reply-To: <20200416160026.16538-1-kirill.shutemov@linux.intel.com>
__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")
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-and-Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
---
mm/khugepaged.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 99d77ffb79c2..6e69dc9a9fb1 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,
--
2.26.1
next prev parent reply other threads:[~2020-04-16 16:01 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-16 16:00 [PATCHv4 0/8] thp/khugepaged improvements and CoW semantics Kirill A. Shutemov
2020-04-16 16:00 ` [PATCHv4 1/8] khugepaged: Add self test Kirill A. Shutemov
2020-04-16 16:00 ` Kirill A. Shutemov [this message]
2020-04-16 16:00 ` [PATCHv4 3/8] khugepaged: Drain all LRU caches before scanning pages Kirill A. Shutemov
2020-04-16 16:00 ` [PATCHv4 4/8] khugepaged: Drain LRU add pagevec after swapin Kirill A. Shutemov
2020-04-17 4:41 ` Andrew Morton
2020-04-17 14:59 ` Kirill A. Shutemov
2020-04-16 16:00 ` [PATCHv4 5/8] khugepaged: Allow to collapse a page shared across fork Kirill A. Shutemov
2020-04-16 16:00 ` [PATCHv4 6/8] khugepaged: Allow to collapse PTE-mapped compound pages Kirill A. Shutemov
2020-04-16 16:00 ` [PATCHv4 7/8] thp: Change CoW semantics for anon-THP Kirill A. Shutemov
2020-04-21 0:48 ` [thp] fd80f22b29: vm-scalability.median 10.3% improvement kernel test robot
2020-04-16 16:00 ` [PATCHv4 8/8] khugepaged: Introduce 'max_ptes_shared' tunable Kirill A. Shutemov
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