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Date: Wed, 26 May 2010 16:34:59 -0400 From: Larry Woodman <lwoodman@...hat.com> To: Rik van Riel <riel@...hat.com> Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Mel Gorman <mel@....ul.ie>, Andrea Arcangeli <aarcange@...hat.com>, Minchan Kim <minchan.kim@...il.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Lee Schermerhorn <Lee.Schermerhorn@...com> Subject: Re: [PATCH 3/5] track the root (oldest) anon_vma On Wed, 2010-05-26 at 15:40 -0400, Rik van Riel wrote: > Subject: track the root (oldest) anon_vma > > 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. > > Signed-off-by: Rik van Riel <riel@...hat.com> > Acked-by: Mel Gorman <mel@....ul.ie> > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Tested and Acked-by: Larry Woodman <lwoodman@...hat.com> > --- > include/linux/rmap.h | 1 + > mm/rmap.c | 18 ++++++++++++++++-- > 2 files changed, 17 insertions(+), 2 deletions(-) > > Index: linux-2.6.34/include/linux/rmap.h > =================================================================== > --- linux-2.6.34.orig/include/linux/rmap.h > +++ linux-2.6.34/include/linux/rmap.h > @@ -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) > > /* > Index: linux-2.6.34/mm/rmap.c > =================================================================== > --- linux-2.6.34.orig/mm/rmap.c > +++ linux-2.6.34/mm/rmap.c > @@ -132,6 +132,11 @@ int anon_vma_prepare(struct vm_area_stru > 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 > avc = anon_vma_chain_alloc(); > if (!avc) > goto out_error_free_anon_vma; > - anon_vma_chain_link(vma, avc, anon_vma); > + > + /* > + * The root anon_vm'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_str > { > 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); > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@...ck.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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