The patch titled Subject: mm: incorporate read-only pages into transparent huge pages has been removed from the -mm tree. Its filename was mm-incorporate-read-only-pages-into-transparent-huge-pages.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx> Subject: mm: incorporate read-only pages into transparent huge pages This patch aims to improve THP collapse rates, by allowing THP collapse in the presence of read-only ptes, like those left in place by do_swap_page after a read fault. Currently THP can collapse 4kB pages into a THP when there are up to khugepaged_max_ptes_none pte_none ptes in a 2MB range. This patch applies the same limit for read-only ptes. The patch was tested with a test program that allocates 800MB of memory, writes to it, and then sleeps. I force the system to swap out all but 190MB of the program by touching other memory. Afterwards, the test program does a mix of reads and writes to its memory, and the memory gets swapped back in. Without the patch, only the memory that did not get swapped out remained in THPs, which corresponds to 24% of the memory of the program. The percentage did not increase over time. With this patch, after 5 minutes of waiting khugepaged had collapsed 50% of the program's memory back into THPs. Test results: With the patch: After swapped out: cat /proc/pid/smaps: Anonymous: 100464 kB AnonHugePages: 100352 kB Swap: 699540 kB Fraction: 99,88 cat /proc/meminfo: AnonPages: 1754448 kB AnonHugePages: 1716224 kB Fraction: 97,82 After swapped in: In a few seconds: cat /proc/pid/smaps: Anonymous: 800004 kB AnonHugePages: 145408 kB Swap: 0 kB Fraction: 18,17 cat /proc/meminfo: AnonPages: 2455016 kB AnonHugePages: 1761280 kB Fraction: 71,74 In 5 minutes: cat /proc/pid/smaps Anonymous: 800004 kB AnonHugePages: 407552 kB Swap: 0 kB Fraction: 50,94 cat /proc/meminfo: AnonPages: 2456872 kB AnonHugePages: 2023424 kB Fraction: 82,35 Without the patch: After swapped out: cat /proc/pid/smaps: Anonymous: 190660 kB AnonHugePages: 190464 kB Swap: 609344 kB Fraction: 99,89 cat /proc/meminfo: AnonPages: 1740456 kB AnonHugePages: 1667072 kB Fraction: 95,78 After swapped in: cat /proc/pid/smaps: Anonymous: 800004 kB AnonHugePages: 190464 kB Swap: 0 kB Fraction: 23,80 cat /proc/meminfo: AnonPages: 2350032 kB AnonHugePages: 1667072 kB Fraction: 70,93 I waited 10 minutes the fractions did not change without the patch. Signed-off-by: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx> Acked-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Sasha Levin <sasha.levin@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 55 ++++++++++++++++++++++++++++++++++----------- 1 file changed, 42 insertions(+), 13 deletions(-) diff -puN mm/huge_memory.c~mm-incorporate-read-only-pages-into-transparent-huge-pages mm/huge_memory.c --- a/mm/huge_memory.c~mm-incorporate-read-only-pages-into-transparent-huge-pages +++ a/mm/huge_memory.c @@ -2117,7 +2117,8 @@ static int __collapse_huge_page_isolate( { struct page *page; pte_t *_pte; - int referenced = 0, none = 0; + int none = 0; + bool referenced = false, writable = false; for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++, address += PAGE_SIZE) { pte_t pteval = *_pte; @@ -2127,7 +2128,7 @@ static int __collapse_huge_page_isolate( else goto out; } - if (!pte_present(pteval) || !pte_write(pteval)) + if (!pte_present(pteval)) goto out; page = vm_normal_page(vma, address, pteval); if (unlikely(!page)) @@ -2137,9 +2138,6 @@ static int __collapse_huge_page_isolate( VM_BUG_ON_PAGE(!PageAnon(page), page); VM_BUG_ON_PAGE(!PageSwapBacked(page), page); - /* cannot use mapcount: can't collapse if there's a gup pin */ - if (page_count(page) != 1) - goto out; /* * We can do it before isolate_lru_page because the * page can't be freed from under us. NOTE: PG_lock @@ -2148,6 +2146,29 @@ static int __collapse_huge_page_isolate( */ if (!trylock_page(page)) goto out; + + /* + * cannot use mapcount: can't collapse if there's a gup pin. + * The page must only be referenced by the scanned process + * and page swap cache. + */ + if (page_count(page) != 1 + !!PageSwapCache(page)) { + unlock_page(page); + goto out; + } + if (pte_write(pteval)) { + writable = true; + } else { + if (PageSwapCache(page) && !reuse_swap_page(page)) { + unlock_page(page); + goto out; + } + /* + * Page is not in the swap cache. It can be collapsed + * into a THP. + */ + } + /* * Isolate the page to avoid collapsing an hugepage * currently in use by the VM. @@ -2164,9 +2185,9 @@ static int __collapse_huge_page_isolate( /* If there is no mapped pte young don't collapse the page */ if (pte_young(pteval) || PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm, address)) - referenced = 1; + referenced = true; } - if (likely(referenced)) + if (likely(referenced && writable)) return 1; out: release_pte_pages(pte, _pte); @@ -2519,11 +2540,12 @@ static int khugepaged_scan_pmd(struct mm { pmd_t *pmd; pte_t *pte, *_pte; - int ret = 0, referenced = 0, none = 0; + int ret = 0, none = 0; struct page *page; unsigned long _address; spinlock_t *ptl; int node = NUMA_NO_NODE; + bool writable = false, referenced = false; VM_BUG_ON(address & ~HPAGE_PMD_MASK); @@ -2542,8 +2564,11 @@ static int khugepaged_scan_pmd(struct mm else goto out_unmap; } - if (!pte_present(pteval) || !pte_write(pteval)) + if (!pte_present(pteval)) goto out_unmap; + if (pte_write(pteval)) + writable = true; + page = vm_normal_page(vma, _address, pteval); if (unlikely(!page)) goto out_unmap; @@ -2560,14 +2585,18 @@ static int khugepaged_scan_pmd(struct mm VM_BUG_ON_PAGE(PageCompound(page), page); if (!PageLRU(page) || PageLocked(page) || !PageAnon(page)) goto out_unmap; - /* cannot use mapcount: can't collapse if there's a gup pin */ - if (page_count(page) != 1) + /* + * cannot use mapcount: can't collapse if there's a gup pin. + * The page must only be referenced by the scanned process + * and page swap cache. + */ + if (page_count(page) != 1 + !!PageSwapCache(page)) goto out_unmap; if (pte_young(pteval) || PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm, address)) - referenced = 1; + referenced = true; } - if (referenced) + if (referenced && writable) ret = 1; out_unmap: pte_unmap_unlock(pte, ptl); _ Patches currently in -mm which might be from ebru.akagunduz@xxxxxxxxx are origin.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html