From mboxrd@z Thu Jan 1 00:00:00 1970 From: kamezawa.hiroyu@jp.fujitsu.com Message-ID: <20795958.1215245782985.kamezawa.hiroyu@jp.fujitsu.com> Date: Sat, 5 Jul 2008 17:16:22 +0900 (JST) Subject: Re: Re: [PATCH] memcg: handle shmem's swap cache (Was 2.6.26-rc8-mm1 In-Reply-To: <486F1967.1030207@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-2022-jp" Content-Transfer-Encoding: 7bit References: <486F1967.1030207@linux.vnet.ibm.com> <20080703020236.adaa51fa.akpm@linux-foundation.org> <20080704180913.bb1a3fc6.kamezawa.hiroyu@jp.fujitsu.com> <486F0976.7010104@linux.vnet.ibm.com> <20080705151146.206071a4.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org Return-Path: To: balbir@linux.vnet.ibm.com Cc: KAMEZAWA Hiroyuki , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, hugh@veritas.com, nishimura@mxp.nes.nec.co.jp, yamamoto@valinux.co.jp List-ID: ----- Original Message ----- >Date: Sat, 05 Jul 2008 12:19:11 +0530 >From: Balbir Singh >To: KAMEZAWA Hiroyuki >CC: Andrew Morton , linux-kernel@vger.kernel.org, > linux-mm@kvack.org, "hugh@veritas.com" , > "nishimura@mxp.nes.nec.co.jp" , > "yamamoto@valinux.co.jp" >Subject: Re: [PATCH] memcg: handle shmem's swap cache (Was 2.6.26-rc8-mm1 > > >KAMEZAWA Hiroyuki wrote: >> On Sat, 05 Jul 2008 11:11:10 +0530 >> Balbir Singh wrote: >> >>> KAMEZAWA Hiroyuki wrote: >>>> My swapcache accounting under memcg patch failed to catch tmpfs(shmem)'s one. >>>> Can I test this under -mm tree ? >>>> (If -mm is busy, I'm not in hurry.) >>>> This patch works well in my box. >>>> = >>>> SwapCache handling fix. >>>> >>>> shmem's swapcache behavior is a little different from anonymous's one and >>>> memcg failed to handle it. This patch tries to fix it. >>>> >>>> After this: >>>> >>>> Any page marked as SwapCache is not uncharged. (delelte_from_swap_cache() >>>> delete the SwapCache flag.) >>>> >>>> To check a shmem-page-cache is alive or not we use >>>> page->mapping && !PageAnon(page) instead of >>>> pc->flags & PAGE_CGROUP_FLAG_CACHE. >>>> >>>> Signed-off-by: KAMEZAWA Hiroyuki >>> Though I am not opposed to this, I do sit up and think if keeping the refe rence >>> count around could avoid this complexity and from my point, the maintenanc e >>> overhead of this logic/code (I fear there might be more special cases :( ) >> >> yes, to me. but we have to fix.. >> >> But I don't like old code's refcnt handling which does >> - increment >> - does this increment was really neccesary ? >> No? ok, decrement it again. >> >> This was much more complex to me than current code. >> At first, what I have to say is "this is a fix against handle-swapcache patch not against remove-refcnt" This complex comes from handle-swapcache. (But it's necessary.) > >That can be redone -- the moment a page is used by a path, refcnt (increment) >it. Undo the same when the page is no longer in use. > >I expect > >rmap path to increment/decrement it on mapping >radix-tree (cache's) to do the same > > >Using a kref we should be able to get this logic right - no? > no What the old code does was - a page is added to rmap (mapcount 0->1) +1 - a page is removed from rmap (mapcount ->0) -1 - a page is added to radix-tree (+1) - a page is removed from radix-tree (-1) All information is recorded in struct page because it exists for. Then, why duplicates information ? It's usually bad habit. >> And old ones will needs the check at treating swap-cache. (it couldn't but if we want) >> >>> The trade-off is complexity versus the overhead of reference counting. >>> >> refcnt was also very complex ;) > >I think that is easier to simply, instead of adding the complex checks we hav e >right now. refcnt is easier to prove as working correct than the checks. About swap-cache, refcnt is just obstacle because you can't handle add-to-swapcache by refcnt. If you want to add refcnt (or some code) for "debug", I have no objection. Thanks, -Kame -- 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