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Commit 746b18d4 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
Browse files

mm: use refcounts for page_lock_anon_vma() 



Convert page_lock_anon_vma() over to use refcounts.  This is done to
prepare for the conversion of anon_vma from spinlock to mutex.

Sadly this inceases the cost of page_lock_anon_vma() from one to two
atomics, a follow up patch addresses this, lets keep that simple for now.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Miller <davem@davemloft.net>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6111e4ca

mm/migrate.c

+4 −13
Original line number Diff line number Diff line
@@ -721,15 +721,11 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, 
		 * Only page_lock_anon_vma() understands the subtleties of

		 * getting a hold on an anon_vma from outside one of its mms.

		 */

		anon_vma = page_lock_anon_vma(page);

		anon_vma = page_get_anon_vma(page);

		if (anon_vma) {

			/*

			 * Take a reference count on the anon_vma if the

			 * page is mapped so that it is guaranteed to

			 * exist when the page is remapped later

			 * Anon page

			 */

			get_anon_vma(anon_vma);

			page_unlock_anon_vma(anon_vma);

		} else if (PageSwapCache(page)) {

			/*

			 * We cannot be sure that the anon_vma of an unmapped
@@ -857,13 +853,8 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, 
		lock_page(hpage);

	}



	if (PageAnon(hpage)) {

		anon_vma = page_lock_anon_vma(hpage);

		if (anon_vma) {

			get_anon_vma(anon_vma);

			page_unlock_anon_vma(anon_vma);

		}

	}

	if (PageAnon(hpage))

		anon_vma = page_get_anon_vma(hpage);



	try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);

mm/rmap.c

+27 −15
Original line number Diff line number Diff line
@@ -337,9 +337,9 @@ void __init anon_vma_init(void) 
 * that the anon_vma pointer from page->mapping is valid if there is a

 * mapcount, we can dereference the anon_vma after observing those.

 */

struct anon_vma *page_lock_anon_vma(struct page *page)

struct anon_vma *page_get_anon_vma(struct page *page)

{

	struct anon_vma *anon_vma, *root_anon_vma;

	struct anon_vma *anon_vma = NULL;

	unsigned long anon_mapping;



	rcu_read_lock();
@@ -350,30 +350,42 @@ struct anon_vma *page_lock_anon_vma(struct page *page) 
		goto out;



	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);

	root_anon_vma = ACCESS_ONCE(anon_vma->root);

	spin_lock(&root_anon_vma->lock);

	if (!atomic_inc_not_zero(&anon_vma->refcount)) {

		anon_vma = NULL;

		goto out;

	}



	/*

	 * If this page is still mapped, then its anon_vma cannot have been

	 * freed.  But if it has been unmapped, we have no security against

	 * the anon_vma structure being freed and reused (for another anon_vma:

	 * SLAB_DESTROY_BY_RCU guarantees that - so the spin_lock above cannot

	 * corrupt): with anon_vma_prepare() or anon_vma_fork() redirecting

	 * anon_vma->root before page_unlock_anon_vma() is called to unlock.

	 * freed.  But if it has been unmapped, we have no security against the

	 * anon_vma structure being freed and reused (for another anon_vma:

	 * SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()

	 * above cannot corrupt).

	 */

	if (page_mapped(page))

		return anon_vma;



	spin_unlock(&root_anon_vma->lock);

	if (!page_mapped(page)) {

		put_anon_vma(anon_vma);

		anon_vma = NULL;

	}

out:

	rcu_read_unlock();

	return NULL;



	return anon_vma;

}



struct anon_vma *page_lock_anon_vma(struct page *page)

{

	struct anon_vma *anon_vma = page_get_anon_vma(page);



	if (anon_vma)

		anon_vma_lock(anon_vma);



	return anon_vma;

}



void page_unlock_anon_vma(struct anon_vma *anon_vma)

{

	anon_vma_unlock(anon_vma);

	rcu_read_unlock();

	put_anon_vma(anon_vma);

}



/*