From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mt1.gw.fujitsu.co.jp ([10.0.50.74]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id mA508OHv029369 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Wed, 5 Nov 2008 09:08:24 +0900 Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 132F645DD7D for ; Wed, 5 Nov 2008 09:08:24 +0900 (JST) Received: from s8.gw.fujitsu.co.jp (s8.gw.fujitsu.co.jp [10.0.50.98]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 8AD8845DD99 for ; Wed, 5 Nov 2008 09:08:23 +0900 (JST) Received: from s8.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s8.gw.fujitsu.co.jp (Postfix) with ESMTP id 6AD4D1DB803C for ; Wed, 5 Nov 2008 09:08:23 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s8.gw.fujitsu.co.jp (Postfix) with ESMTP id 15DB71DB8042 for ; Wed, 5 Nov 2008 09:08:23 +0900 (JST) Date: Wed, 5 Nov 2008 09:07:49 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC][PATCH 2/5] memcg : handle swap cache Message-Id: <20081105090749.a8756b03.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20081104192822.fc87868b.nishimura@mxp.nes.nec.co.jp> References: <20081031115057.6da3dafd.kamezawa.hiroyu@jp.fujitsu.com> <20081031115411.25478878.kamezawa.hiroyu@jp.fujitsu.com> <20081104174201.9e2dc44c.nishimura@mxp.nes.nec.co.jp> <20081104180429.4e47875e.kamezawa.hiroyu@jp.fujitsu.com> <20081104192822.fc87868b.nishimura@mxp.nes.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Daisuke Nishimura Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "balbir@linux.vnet.ibm.com" , hugh@veritas.com, taka@valinux.co.jp List-ID: On Tue, 4 Nov 2008 19:28:22 +0900 Daisuke Nishimura wrote: > On Tue, 4 Nov 2008 18:04:29 +0900, KAMEZAWA Hiroyuki wrote: > > On Tue, 4 Nov 2008 17:42:01 +0900 > > Daisuke Nishimura wrote: > > > > > > +#ifdef CONFIG_SWAP > > > > +int mem_cgroup_cache_charge_swapin(struct page *page, > > > > + struct mm_struct *mm, gfp_t mask) > > > > +{ > > > > + int ret = 0; > > > > + > > > > + if (mem_cgroup_subsys.disabled) > > > > + return 0; > > > > + if (unlikely(!mm)) > > > > + mm = &init_mm; > > > > + > > > > + ret = mem_cgroup_charge_common(page, mm, mask, > > > > + MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL); > > > > + /* > > > > + * The page may be dropped from SwapCache because we don't have > > > > + * lock_page().This may cause charge-after-uncharge trouble. > > > > + * Fix it up here. (the caller have refcnt to this page and > > > > + * page itself is guaranteed not to be freed.) > > > > + */ > > > > + if (ret && !PageSwapCache(page)) > > > > + mem_cgroup_uncharge_swapcache(page); > > > > + > > > Hmm.. after [5/5], mem_cgroup_cache_charge_swapin has 'locked' parameter, > > > calls lock_page(if !locked), and checks PageSwapCache under page lock. > > > > > > Why not doing it in this patch? > > > > > > > My intention is to guard swap_cgroup by lock_page() against SwapCache. > > In Mem+Swap controller. we get "memcg" from information in page->private. > > I think we need lock_page(), there. > > > > But here, we don't refer page->private information. > > I think we don't need lock_page() because there is no inofrmation we depends on. > > > I just thought it would be simpler to check PageSwapCache after holding > page lock rather than to handle the case that the page might be removed from > swap cache. > > And to be honest, I can't understand the "charge-after-uncharge trouble". > Could you explain more? > Maybe typical case is following. __delete_from_swapcache can happen while the page is unlocked. == some other thread. page = shmem_swapin() swapin_readahead(); # page is SwapCache here. # but this page is not locked. ___delete_from_swapcache(page) # This is not SwapCache. => uncharge swapcache. mem_cgroup_charge_cache_swapin(); { charge(); # charged this page but we don't know this is still swapcache. if (!PageSwapCache(page)) { # Oh we should unroll this. } } = 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