From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id 9C60F6B0225 for ; Thu, 13 May 2010 09:12:04 -0400 (EDT) Message-ID: <4BEBFA82.2000301@redhat.com> Date: Thu, 13 May 2010 09:11:30 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 5/5] extend KSM refcounts to the anon_vma root References: <20100512134111.467fb6c2@annuminas.surriel.com> <20100512210706.GQ24989@csn.ul.ie> <4BEB18FE.1090808@redhat.com> <20100513112603.GB27949@csn.ul.ie> In-Reply-To: <20100513112603.GB27949@csn.ul.ie> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Andrew Morton , Andrea Arcangeli , Minchan Kim , Linux-MM , KAMEZAWA Hiroyuki , LKML , Linus Torvalds List-ID: On 05/13/2010 07:26 AM, Mel Gorman wrote: > On Wed, May 12, 2010 at 05:09:18PM -0400, Rik van Riel wrote: >> On 05/12/2010 05:07 PM, Mel Gorman wrote: >>> On Wed, May 12, 2010 at 01:41:11PM -0400, Rik van Riel wrote: >>>> Subject: extend KSM refcounts to the anon_vma root >>>> >>>> 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 >>>> --- >>>> include/linux/rmap.h | 12 ++++++++++++ >>>> mm/ksm.c | 17 ++++++----------- >>>> mm/rmap.c | 45 ++++++++++++++++++++++++++++++++++++++++++++- >>>> 3 files changed, 62 insertions(+), 12 deletions(-) >>>> >>>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >>>> index 33ffe14..387d40c 100644 >>>> --- a/include/linux/rmap.h >>>> +++ b/include/linux/rmap.h >>>> @@ -126,6 +126,18 @@ int anon_vma_fork(struct vm_area_struct *, struct vm_area_struct *); >>>> void __anon_vma_link(struct vm_area_struct *); >>>> void anon_vma_free(struct anon_vma *); >>>> >>>> +#ifdef CONFIG_KSM >>>> +static inline void get_anon_vma(struct anon_vma *anon_vma) >>>> +{ >>>> + atomic_inc(&anon_vma->ksm_refcount); >>>> +} >>>> + >>>> +void drop_anon_vma(struct anon_vma *); >>>> +#else >>>> +#define get_anon_vma(x) do {} while(0) >>>> +#define drop_anon_vma(x) do {} while(0) >>>> +#endif >>>> + >>>> static inline void anon_vma_merge(struct vm_area_struct *vma, >>>> struct vm_area_struct *next) >>>> { >>>> diff --git a/mm/ksm.c b/mm/ksm.c >>>> index 7ca0dd7..9f2acc9 100644 >>>> --- a/mm/ksm.c >>>> +++ b/mm/ksm.c >>>> @@ -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->ksm_refcount); >>>> + get_anon_vma(anon_vma); >>>> } >>> >>> I'm not quite getting this. Here, we get the local anon_vma so we >>> increment its reference count and later we drop it but without a >>> refcount taken on the root anon_vma, why is it guaranteed to stay >>> around? >> >> Because anon_vma_fork takes a reference count on the root anon_vma, >> the VMA we take a refcount on will either have a refcount on the >> root, or it is the root. >> > > Sorry, I'm still not getting it. anon_vma_fork keeps the refcount around > during fork but what about during exit? It is kept around all the way from fork until exit. -- All rights reversed -- 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