Commit 03ef83af authored Aug 26, 2009 by Minchan Kim Committed by Linus Torvalds Aug 26, 2009

mm: fix for infinite churning of mlocked pages



An mlocked page might lose the isolatation race.  This causes the page to
clear PG_mlocked while it remains in a VM_LOCKED vma.  This means it can
be put onto the [in]active list.  We can rescue it by using try_to_unmap()
in shrink_page_list().

But now, As Wu Fengguang pointed out, vmscan has a bug.  If the page has
PG_referenced, it can't reach try_to_unmap() in shrink_page_list() but is
put into the active list.  If the page is referenced repeatedly, it can
remain on the [in]active list without being moving to the unevictable
list.

This patch fixes it.

Reported-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <&lt;kosaki.motohiro@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b62e408c

mm/rmap.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -358,6 +358,7 @@ static int page_referenced_one(struct page *page,
		*/
		if (vma->vm_flags & VM_LOCKED) {
		mapcount = 1; / break early from loop */
		*vm_flags \|= VM_LOCKED;
		goto out_unmap;
		}

mm/vmscan.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -630,9 +630,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,

		referenced = page_referenced(page, 1,
		sc->mem_cgroup, &vm_flags);
		/* In active use or really unfreeable? Activate it. */
		/*
		* In active use or really unfreeable? Activate it.
		* If page which have PG_mlocked lost isoltation race,
		* try_to_unmap moves it to unevictable list
		*/
		if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
		referenced && page_mapping_inuse(page))
		referenced && page_mapping_inuse(page)
		&& !(vm_flags & VM_LOCKED))
		goto activate_locked;

		/*