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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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17
mm/ksm.c
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@ -318,19 +318,14 @@ static void hold_anon_vma(struct rmap_item *rmap_item,
struct anon_vma *anon_vma)
{
rmap_item->anon_vma = anon_vma;
atomic_inc(&anon_vma->external_refcount);
get_anon_vma(anon_vma);
}
static void drop_anon_vma(struct rmap_item *rmap_item)
static void ksm_drop_anon_vma(struct rmap_item *rmap_item)
{
struct anon_vma *anon_vma = rmap_item->anon_vma;
if (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);
}
drop_anon_vma(anon_vma);
}
/*
@ -415,7 +410,7 @@ static void break_cow(struct rmap_item *rmap_item)
* It is not an accident that whenever we want to break COW
* to undo, we also need to drop a reference to the anon_vma.
*/
drop_anon_vma(rmap_item);
ksm_drop_anon_vma(rmap_item);
down_read(&mm->mmap_sem);
if (ksm_test_exit(mm))
@ -470,7 +465,7 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node)
ksm_pages_sharing--;
else
ksm_pages_shared--;
drop_anon_vma(rmap_item);
ksm_drop_anon_vma(rmap_item);
rmap_item->address &= PAGE_MASK;
cond_resched();
}
@ -558,7 +553,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
else
ksm_pages_shared--;
drop_anon_vma(rmap_item);
ksm_drop_anon_vma(rmap_item);
rmap_item->address &= PAGE_MASK;
} else if (rmap_item->address & UNSTABLE_FLAG) {