From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 26 Sep 2008 15:54:33 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 9/12] memcg allocate all page_cgroup at boot Message-Id: <20080926155433.81eb520b.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20080926145422.327fb53f.nishimura@mxp.nes.nec.co.jp> References: <20080925151124.25898d22.kamezawa.hiroyu@jp.fujitsu.com> <20080925153206.281243dc.kamezawa.hiroyu@jp.fujitsu.com> <20080926100022.8bfb8d4d.nishimura@mxp.nes.nec.co.jp> <20080926104336.d96ab5bd.kamezawa.hiroyu@jp.fujitsu.com> <20080926110550.2292287b.kamezawa.hiroyu@jp.fujitsu.com> <20080926145422.327fb53f.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" , "balbir@linux.vnet.ibm.com" , "xemul@openvz.org" , Andrew Morton , LKML , Dave Hansen , ryov@valinux.co.jp List-ID: On Fri, 26 Sep 2008 14:54:22 +0900 Daisuke Nishimura wrote: > > > There is a SwapCache which is referred from 2 process, A, B. > > > A maps it. > > > B doesn't maps it. > > > > > > And now, process A exits. > > > > > > CPU0(process A) CPU1 (process B) > > > > > > zap_pte_range() > > > => page remove from rmap => charge() (do_swap_page) > > > => set page->mapcount->0 > > > => uncharge() => set page->mapcount=1 > > > > > > This race is what patch 12/12 is fixed. > > > This only happens on cursed SwapCache. > > > > > Sorry, my brain seems to be sleeping.. above page_mapped() check doesn't > > help this situation. Maybe this page_mapped() check is not necessary > > because it's of no use. > > > > I think this kind of problem will not be fixed until we handle SwapCache. > > > I've not fully understood yet what [12/12] does, but if we handle > swapcache properly, [12/12] would become unnecessary? > Maybe yes. we treat swapcache under lock_page(). > If so, how about handling swapcache instead of adding new interface? > I think it can be done independent of mem+swap. > Hmm, worth to be considered. But I'll reuse the interface itself for othres (shmem, migrate, move_account etc) But, in previous trial of SwapCache handling, we saw many troubles. Then, I'd like to go carefully step by step to handle that. 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