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Commit 31e855ea authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 93d17715

mm/ksm.c

+6 −20
Original line number Diff line number Diff line
@@ -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;

}