From 29ad768cfc08611a4c1070d0f13f82eeea2bac7b Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Thu, 13 Jan 2011 15:47:19 -0800 Subject: [PATCH] thp: KSM on THP This makes KSM full operational with THP pages. Subpages are scanned while the hugepage is still in place and delivering max cpu performance, and only if there's a match and we're going to deduplicate memory, the single hugepages with the subpage match is split. There will be no false sharing between ksmd and khugepaged. khugepaged won't collapse 2m virtual regions with KSM pages inside. ksmd also should only split pages when the checksum matches and we're likely to split an hugepage for some long living ksm page (usual ksm heuristic to avoid sharing pages that get de-cowed). Signed-off-by: Andrea Arcangeli Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/ksm.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 58 insertions(+), 9 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index e2b0afd0a031..4d5a681923bb 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -412,6 +412,29 @@ out: up_read(&mm->mmap_sem); } +static struct page *page_trans_compound_anon(struct page *page) +{ + if (PageTransCompound(page)) { + struct page *head; + head = compound_head(page); + /* + * head may be a dangling pointer. + * __split_huge_page_refcount clears PageTail + * before overwriting first_page, so if + * PageTail is still there it means the head + * pointer isn't dangling. + */ + if (head != page) { + smp_rmb(); + if (!PageTransCompound(page)) + return NULL; + } + if (PageAnon(head)) + return head; + } + return NULL; +} + static struct page *get_mergeable_page(struct rmap_item *rmap_item) { struct mm_struct *mm = rmap_item->mm; @@ -431,7 +454,7 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item) page = follow_page(vma, addr, FOLL_GET); if (IS_ERR_OR_NULL(page)) goto out; - if (PageAnon(page) && !PageTransCompound(page)) { + if (PageAnon(page) || page_trans_compound_anon(page)) { flush_anon_page(vma, page, addr); flush_dcache_page(page); } else { @@ -709,6 +732,7 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page, if (addr == -EFAULT) goto out; + BUG_ON(PageTransCompound(page)); ptep = page_check_address(page, mm, addr, &ptl, 0); if (!ptep) goto out; @@ -784,6 +808,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, goto out; pmd = pmd_offset(pud, addr); + BUG_ON(pmd_trans_huge(*pmd)); if (!pmd_present(*pmd)) goto out; @@ -811,6 +836,33 @@ out: return err; } +static int page_trans_compound_anon_split(struct page *page) +{ + int ret = 0; + struct page *transhuge_head = page_trans_compound_anon(page); + if (transhuge_head) { + /* Get the reference on the head to split it. */ + if (get_page_unless_zero(transhuge_head)) { + /* + * Recheck we got the reference while the head + * was still anonymous. + */ + if (PageAnon(transhuge_head)) + ret = split_huge_page(transhuge_head); + else + /* + * Retry later if split_huge_page run + * from under us. + */ + ret = 1; + put_page(transhuge_head); + } else + /* Retry later if split_huge_page run from under us. */ + ret = 1; + } + return ret; +} + /* * try_to_merge_one_page - take two pages and merge them into one * @vma: the vma that holds the pte pointing to page @@ -831,6 +883,9 @@ static int try_to_merge_one_page(struct vm_area_struct *vma, if (!(vma->vm_flags & VM_MERGEABLE)) goto out; + if (PageTransCompound(page) && page_trans_compound_anon_split(page)) + goto out; + BUG_ON(PageTransCompound(page)); if (!PageAnon(page)) goto out; @@ -1285,14 +1340,8 @@ next_mm: cond_resched(); continue; } - if (PageTransCompound(*page)) { - put_page(*page); - ksm_scan.address &= HPAGE_PMD_MASK; - ksm_scan.address += HPAGE_PMD_SIZE; - cond_resched(); - continue; - } - if (PageAnon(*page)) { + if (PageAnon(*page) || + page_trans_compound_anon(*page)) { flush_anon_page(vma, *page, ksm_scan.address); flush_dcache_page(*page); rmap_item = get_next_rmap_item(slot, -- 2.34.1