From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id A868A600385 for ; Thu, 27 May 2010 09:48:51 -0400 (EDT) Received: by pzk11 with SMTP id 11so4073412pzk.28 for ; Thu, 27 May 2010 06:48:50 -0700 (PDT) Date: Thu, 27 May 2010 22:48:41 +0900 From: Minchan Kim Subject: Re: [PATCH 3/5] track the root (oldest) anon_vma Message-ID: <20100527134841.GC2112@barrios-desktop> References: <20100526153819.6e5cec0d@annuminas.surriel.com> <20100526154010.3904df5c@annuminas.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100526154010.3904df5c@annuminas.surriel.com> Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mel Gorman , Andrea Arcangeli , KAMEZAWA Hiroyuki , Lee Schermerhorn List-ID: On Wed, May 26, 2010 at 03:40:10PM -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 > Acked-by: Mel Gorman > Acked-by: KAMEZAWA Hiroyuki Reviewed-by: Minchan Kim Except below one minor type. > --- > 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 anon_vma's -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org