From 31e855ea7173bdb0520f9684580423a9560f66e0 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 14 Dec 2009 17:59:17 -0800 Subject: [PATCH] ksm: remove redundancies when merging page There is no need for replace_page() to calculate a write-protected prot vm_page_prot must already be write-protected for an anonymous page (see mm/memory.c do_anonymous_page() for similar reliance on vm_page_prot). There is no need for try_to_merge_one_page() to get_page and put_page on newpage and oldpage: in every case we already hold a reference to each of them. But some instinct makes me move try_to_merge_one_page()'s unlock_page of oldpage down after replace_page(): that doesn't increase contention on the ksm page, and makes thinking about the transition easier. Signed-off-by: Hugh Dickins Cc: Izik Eidus Cc: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/ksm.c | 26 ++++++-------------------- 1 file changed, 6 insertions(+), 20 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 133ea2ca8384..fdd7d5faa90c 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -647,7 +647,7 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page, * Check that no O_DIRECT or similar I/O is in progress on the * page */ - if ((page_mapcount(page) + 2 + swapped) != page_count(page)) { + if (page_mapcount(page) + 1 + swapped != page_count(page)) { set_pte_at_notify(mm, addr, ptep, entry); goto out_unlock; } @@ -682,11 +682,8 @@ static int replace_page(struct vm_area_struct *vma, struct page *oldpage, pte_t *ptep; spinlock_t *ptl; unsigned long addr; - pgprot_t prot; int err = -EFAULT; - prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE); - addr = page_address_in_vma(oldpage, vma); if (addr == -EFAULT) goto out; @@ -714,7 +711,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *oldpage, flush_cache_page(vma, addr, pte_pfn(*ptep)); ptep_clear_flush(vma, addr, ptep); - set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot)); + set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, vma->vm_page_prot)); page_remove_rmap(oldpage); put_page(oldpage); @@ -746,13 +743,9 @@ static int try_to_merge_one_page(struct vm_area_struct *vma, if (!(vma->vm_flags & VM_MERGEABLE)) goto out; - if (!PageAnon(oldpage)) goto out; - get_page(newpage); - get_page(oldpage); - /* * We need the page lock to read a stable PageSwapCache in * write_protect_page(). We use trylock_page() instead of @@ -761,25 +754,18 @@ static int try_to_merge_one_page(struct vm_area_struct *vma, * then come back to this page when it is unlocked. */ if (!trylock_page(oldpage)) - goto out_putpage; + goto out; /* * If this anonymous page is mapped only here, its pte may need * to be write-protected. If it's mapped elsewhere, all of its * ptes are necessarily already write-protected. But in either * case, we need to lock and check page_count is not raised. */ - if (write_protect_page(vma, oldpage, &orig_pte)) { - unlock_page(oldpage); - goto out_putpage; - } - unlock_page(oldpage); - - if (pages_identical(oldpage, newpage)) + if (write_protect_page(vma, oldpage, &orig_pte) == 0 && + pages_identical(oldpage, newpage)) err = replace_page(vma, oldpage, newpage, orig_pte); -out_putpage: - put_page(oldpage); - put_page(newpage); + unlock_page(oldpage); out: return err; } -- 2.30.2