From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id DE2018D0039 for ; Mon, 7 Mar 2011 21:06:08 -0500 (EST) Date: Tue, 8 Mar 2011 11:04:43 +0900 From: Daisuke Nishimura Subject: Re: [PATCH] memcg: fix to leave pages on wrong LRU with FUSE. Message-Id: <20110308110443.47136fc1.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20110308100242.3075e2c7.kamezawa.hiroyu@jp.fujitsu.com> References: <20110307150049.d42d046d.kamezawa.hiroyu@jp.fujitsu.com> <20110308095939.58100cfd.nishimura@mxp.nes.nec.co.jp> <20110308100242.3075e2c7.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "balbir@linux.vnet.ibm.com" , "akpm@linux-foundation.org" , miklos@szeredi.hu, Daisuke Nishimura On Tue, 8 Mar 2011 10:02:42 +0900 KAMEZAWA Hiroyuki wrote: > On Tue, 8 Mar 2011 09:59:39 +0900 > Daisuke Nishimura wrote: > > > On Mon, 7 Mar 2011 15:00:49 +0900 > > KAMEZAWA Hiroyuki wrote: > > > > > At this point, I'm not sure this is a fix for > > > https://bugzilla.kernel.org/show_bug.cgi?id=30432. > > > > > > The behavior seems very similar to SwapCache case and this is a possible > > > bug and this patch can be a fix. Nishimura-san, how do you think ? > > > > > As long as I can read the source code, I also think this is a possible bug. > > > > > But I'm not sure how to test this....please review. > > > > > > = > > > fs/fuse/dev.c::fuse_try_move_page() does > > > > > > (1) remove a page from page cache by ->steal() > > > (2) re-add the page to page cache > > > (3) link the page to LRU if it was _not_ on LRU at (1) > > > > > > > > > This implies the page can be _on_ LRU when add_to_page_cache_locked() is called. > > > So, the page is added to a memory cgroup while it's on LRU. > > > > > > This is the same behavior as SwapCache, 'newly charged pages may be on LRU' > > > and needs special care as > > > - remove page from old memcg's LRU before overwrite pc->mem_cgroup. > > > - add page to new memcg's LRU after overwrite pc->mem_cgroup. > > > > > > So, reusing SwapCache code with renaming for fix. > > > > > > Note: a page on pagevec(LRU). > > > > > > If a page is not PageLRU(page) but on pagevec(LRU), it may be added to LRU > > > while we overwrite page->mapping. But in that case, PCG_USED bit of > > > the page_cgroup is not set and the page_cgroup will not be added to > > > wrong memcg's LRU. So, this patch's logic will work fine. > > > (It has been tested with SwapCache.) > > > > > As for SwapCache, mem_cgroup_lru_add_after_commit() will be allways called, > > and it will link the page to LRU. But, if I read this patch correctly, > > a page cache on pagevec may not be added to a *proper* memcg's LRU. > > > > lru_add_drain() mem_cgroup_cache_charge() > > ---------------------------------------------------------- > > if (!PageLRU()) > > SetPageLRU() > > add_page_to_lru_list() > > mem_cgroup_add_lru_list() > > -> do nothing > > mem_cgroup_charge_common() > > mem_cgroup_commit_charge() > > -> set PCG_USED > > > > Hmm, yes, that's possible case. > > So, PageLRU() && !PcgAcctLru(pc) should be checked after commit ? > I think so, as mem_cgroup_lru_add_after_commit() does. > I think we can add optimization later (add per-memcg-lru-pegecgrou-vec or some) > In current mmotm, fuse uses replace_page_cache(), which uses mem_cgroup_(prepare|end)_migration(), so I think we can handle this problem in a different way instead of changing mem_cgroup_cache_charge(), which I think is a fast-path operation. Thanks, Daisuke Nishimura. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org