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mm: extend KSM refcounts to the anon_vma root

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KSM reference counts can cause an anon_vma to exist after the processe it
belongs to have already exited.  Because the anon_vma lock now lives in
the root anon_vma, we need to ensure that the root anon_vma stays around
until after all the "child" anon_vmas have been freed.

The obvious way to do this is to have a "child" anon_vma take a reference
to the root in anon_vma_fork.  When the anon_vma is freed at munmap or
process exit, we drop the refcount in anon_vma_unlink and possibly free
the root anon_vma.

The KSM anon_vma reference count function also needs to be modified to
deal with the possibility of freeing 2 levels of anon_vma.  The easiest
way to do this is to break out the KSM magic and make it generic.

When compiling without CONFIG_KSM, this code is compiled out.

Signed-off-by: Rik van Riel <[email protected]>
Tested-by: Larry Woodman <[email protected]>
Acked-by: Larry Woodman <[email protected]>
Reviewed-by: Minchan Kim <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Tested-by: Dave Young <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Rik van Riel 2010-08-09 17:18:41 -07:00 • committed by Linus Torvalds
commit 76545066c8
4 changed files with 69 additions and 19 deletions
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10
mm/migrate.c
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@ -639,7 +639,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
* exist when the page is remapped later
*/
anon_vma = page_anon_vma(page);
atomic_inc(&anon_vma->external_refcount);
get_anon_vma(anon_vma);
}
}
@ -682,12 +682,8 @@ skip_unmap:
rcu_unlock:
/* Drop an anon_vma reference if we took one */
if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
int empty = list_empty(&anon_vma->head);
anon_vma_unlock(anon_vma);
if (empty)
anon_vma_free(anon_vma);
}
if (anon_vma)
drop_anon_vma(anon_vma);
if (rcu_locked)
rcu_read_unlock();