From: Chengming Zhou <chengming.zhou@linux.dev> mainline inclusion from mainline-v6.11-rc1 commit ac90c56bbd734addc9bfb4567f64f1c180c64f5d category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/10169 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- Patch series "mm/ksm: cmp_and_merge_page() optimizations and cleanup", v2. This series mainly optimizes cmp_and_merge_page() to have more efficient separate code flow for ksm page and non-ksm anon page. - ksm page: don't need to calculate the checksum obviously. - anon page: don't need to search stable tree if changing fast and try to merge with zero page before searching ksm page on stable tree. Please see the patch-2 for details. Patch-3 is cleanup also a little optimization for the chain()/chain_prune interfaces, which made the stable_tree_search()/stable_tree_insert() over complex. I have done simple testing using "hackbench -g 1 -l 300000" (maybe I need to use a better workload) on my machine, have seen a little CPU usage decrease of ksmd and some improvements of cmp_and_merge_page() latency: We can see the latency of cmp_and_merge_page() when handling non-ksm anon pages has been improved. This patch (of 3): In preparation for later changes, refactor out a new function called try_to_merge_with_zero_page(), which tries to merge with zero page. Link: https://lkml.kernel.org/r/20240621-b4-ksm-scan-optimize-v2-0-1c328aa9e30b@li... Link: https://lkml.kernel.org/r/20240621-b4-ksm-scan-optimize-v2-1-1c328aa9e30b@li... Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Stefan Roesch <shr@devkernel.io> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com> --- mm/hugetlb.c | 1 - mm/ksm.c | 70 ++++++++++++++++++++++++++++++---------------------- 2 files changed, 40 insertions(+), 31 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index f9ecf50a8f74..88164254cebc 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2703,7 +2703,6 @@ static int gather_surplus_pages(struct hstate *h, long delta) retry: spin_unlock_irq(&hugetlb_lock); for (i = 0; i < needed; i++) { - folio = NULL; for_each_node_mask(node, cpuset_current_mems_allowed) { if (!mbind_nodemask || node_isset(node, *mbind_nodemask)) { folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h), diff --git a/mm/ksm.c b/mm/ksm.c index 0de3de6df144..7e1738b0fb69 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1347,6 +1347,44 @@ static int try_to_merge_one_page(struct vm_area_struct *vma, return err; } +/* + * This function returns 0 if the pages were merged or if they are + * no longer merging candidates (e.g., VMA stale), -EFAULT otherwise. + */ +static int try_to_merge_with_zero_page(struct ksm_rmap_item *rmap_item, + struct page *page) +{ + struct mm_struct *mm = rmap_item->mm; + int err = -EFAULT; + + /* + * Same checksum as an empty page. We attempt to merge it with the + * appropriate zero page if the user enabled this via sysfs. + */ + if (ksm_use_zero_pages && (rmap_item->oldchecksum == zero_checksum)) { + struct vm_area_struct *vma; + + mmap_read_lock(mm); + vma = find_mergeable_vma(mm, rmap_item->address); + if (vma) { + err = try_to_merge_one_page(vma, page, + ZERO_PAGE(rmap_item->address)); + trace_ksm_merge_one_page( + page_to_pfn(ZERO_PAGE(rmap_item->address)), + rmap_item, mm, err); + } else { + /* + * If the vma is out of date, we do not need to + * continue. + */ + err = 0; + } + mmap_read_unlock(mm); + } + + return err; +} + /* * try_to_merge_with_ksm_page - like try_to_merge_two_pages, * but no new kernel page is allocated: kpage must already be a ksm page. @@ -2117,7 +2155,6 @@ static void stable_tree_append(struct ksm_rmap_item *rmap_item, */ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item) { - struct mm_struct *mm = rmap_item->mm; struct ksm_rmap_item *tree_rmap_item; struct page *tree_page = NULL; struct ksm_stable_node *stable_node; @@ -2186,36 +2223,9 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite return; } - /* - * Same checksum as an empty page. We attempt to merge it with the - * appropriate zero page if the user enabled this via sysfs. - */ - if (ksm_use_zero_pages && (checksum == zero_checksum)) { - struct vm_area_struct *vma; + if (!try_to_merge_with_zero_page(rmap_item, page)) + return; - mmap_read_lock(mm); - vma = find_mergeable_vma(mm, rmap_item->address); - if (vma) { - err = try_to_merge_one_page(vma, page, - ZERO_PAGE(rmap_item->address)); - trace_ksm_merge_one_page( - page_to_pfn(ZERO_PAGE(rmap_item->address)), - rmap_item, mm, err); - } else { - /* - * If the vma is out of date, we do not need to - * continue. - */ - err = 0; - } - mmap_read_unlock(mm); - /* - * In case of failure, the page was not really empty, so we - * need to continue. Otherwise we're done. - */ - if (!err) - return; - } tree_rmap_item = unstable_tree_search_insert(rmap_item, page, &tree_page); if (tree_rmap_item) { -- 2.43.0