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mm: track the root (oldest) anon_vma

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Track the root (oldest) anon_vma in each anon_vma tree.  Because we only
take the lock on the root anon_vma, we cannot use the lock on higher-up
anon_vmas to lock anything.  This makes it impossible to do an indirect
lookup of the root anon_vma, since the data structures could go away from
under us.

However, a direct pointer is safe because the root anon_vma is always the
last one that gets freed on munmap or exit, by virtue of the same_vma list
order and unlink_anon_vmas walking the list forward.

[akpm@linux-foundation.org: fix typo]
Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: Larry Woodman <lwoodman@redhat.com>
Acked-by: Larry Woodman <lwoodman@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rik van Riel 2010-08-09 17:18:39 -07:00 committed by Linus Torvalds
parent cba48b98f2
commit 5c341ee1df
2 changed files with 17 additions and 2 deletions
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1
include/linux/rmap.h
View file

@ -26,6 +26,7 @@
*/
struct anon_vma {
spinlock_t lock; /* Serialize access to vma list */
struct anon_vma *root; /* Root of this anon_vma tree */
#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
/*

18
mm/rmap.c
View file

@ -132,6 +132,11 @@ int anon_vma_prepare(struct vm_area_struct *vma)
if (unlikely(!anon_vma))
goto out_enomem_free_avc;
allocated = anon_vma;
/*
* This VMA had no anon_vma yet. This anon_vma is
* the root of any anon_vma tree that might form.
*/
anon_vma->root = anon_vma;
}
anon_vma_lock(anon_vma);
@ -224,9 +229,15 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
avc = anon_vma_chain_alloc();
if (!avc)
goto out_error_free_anon_vma;
anon_vma_chain_link(vma, avc, anon_vma);
/*
* The root anon_vma's spinlock is the lock actually used when we
* lock any of the anon_vmas in this anon_vma tree.
*/
anon_vma->root = pvma->anon_vma->root;
/* Mark this anon_vma as the one where our new (COWed) pages go. */
vma->anon_vma = anon_vma;
anon_vma_chain_link(vma, avc, anon_vma);
return 0;
@ -261,7 +272,10 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
{
struct anon_vma_chain *avc, *next;
/* Unlink each anon_vma chained to the VMA. */
/*
* Unlink each anon_vma chained to the VMA. This list is ordered
* from newest to oldest, ensuring the root anon_vma gets freed last.
*/
list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
anon_vma_unlink(avc);
list_del(&avc->same_vma);