From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sd0109e.au.ibm.com (d23rh905.au.ibm.com [202.81.18.225]) by e23smtp01.au.ibm.com (8.13.1/8.13.1) with ESMTP id m656njwE005148 for ; Sat, 5 Jul 2008 16:49:45 +1000 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by sd0109e.au.ibm.com (8.13.8/8.13.8/NCO v9.0) with ESMTP id m656nGbA271922 for ; Sat, 5 Jul 2008 16:49:16 +1000 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m656nGvQ029819 for ; Sat, 5 Jul 2008 16:49:16 +1000 Message-ID: <486F1967.1030207@linux.vnet.ibm.com> Date: Sat, 05 Jul 2008 12:19:11 +0530 From: Balbir Singh Reply-To: balbir@linux.vnet.ibm.com MIME-Version: 1.0 Subject: Re: [PATCH] memcg: handle shmem's swap cache (Was 2.6.26-rc8-mm1 References: <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> In-Reply-To: <20080705151146.206071a4.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: 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" List-ID: 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 reference >> count around could avoid this complexity and from my point, the maintenance >> 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. > 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? > 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 have right now. refcnt is easier to prove as working correct than the checks. -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL -- 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