From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id D070A6B01F0 for ; Mon, 5 Apr 2010 22:06:24 -0400 (EDT) Received: from m5.gw.fujitsu.co.jp ([10.0.50.75]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o3626Lsc027177 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Tue, 6 Apr 2010 11:06:21 +0900 Received: from smail (m5 [127.0.0.1]) by outgoing.m5.gw.fujitsu.co.jp (Postfix) with ESMTP id 5047845DE54 for ; Tue, 6 Apr 2010 11:06:21 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (s5.gw.fujitsu.co.jp [10.0.50.95]) by m5.gw.fujitsu.co.jp (Postfix) with ESMTP id 226D745DE51 for ; Tue, 6 Apr 2010 11:06:21 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id EDBD31DB805E for ; Tue, 6 Apr 2010 11:06:20 +0900 (JST) Received: from m108.s.css.fujitsu.com (m108.s.css.fujitsu.com [10.249.87.108]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 904C71DB8043 for ; Tue, 6 Apr 2010 11:06:20 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio In-Reply-To: <20100406015045.GA7870@localhost> References: <20100406012536.GB18672@sli10-desk.sh.intel.com> <20100406015045.GA7870@localhost> Message-Id: <20100406105324.7E30.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Tue, 6 Apr 2010 11:06:19 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: kosaki.motohiro@jp.fujitsu.com, "Li, Shaohua" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , Rik van Riel List-ID: > On Tue, Apr 06, 2010 at 09:25:36AM +0800, Li, Shaohua wrote: > > On Sun, Apr 04, 2010 at 10:19:06PM +0800, KOSAKI Motohiro wrote: > > > > On Fri, Apr 02, 2010 at 05:14:38PM +0800, KOSAKI Motohiro wrote: > > > > > > > > This patch makes a lot of sense than previous. however I think <1% anon ratio > > > > > > > > shouldn't happen anyway because file lru doesn't have reclaimable pages. > > > > > > > > <1% seems no good reclaim rate. > > > > > > > > > > > > > > Oops, the above mention is wrong. sorry. only 1 page is still too big. > > > > > > > because under streaming io workload, the number of scanning anon pages should > > > > > > > be zero. this is very strong requirement. if not, backup operation will makes > > > > > > > a lot of swapping out. > > > > > > Sounds there is no big impact for the workload which you mentioned with the patch. > > > > > > please see below descriptions. > > > > > > I updated the description of the patch as fengguang suggested. > > > > > > > > > > Umm.. sorry, no. > > > > > > > > > > "one fix but introduce another one bug" is not good deal. instead, > > > > > I'll revert the guilty commit at first as akpm mentioned. > > > > Even we revert the commit, the patch still has its benefit, as it increases > > > > calculation precision, right? > > > > > > no, you shouldn't ignore the regression case. > > > I don't think this is serious. In my calculation, there is only 1 page swapped out > > for 6G anonmous memory. 1 page should haven't any performance impact. > > 1 anon page scanned for every N file pages scanned? > > Is N a _huge_ enough ratio so that the anon list will be very light scanned? > > Rik: here is a little background. The problem is, the VM are couteniously discarding no longer used file cache. if we are scan extra anon 1 page, we will observe tons swap usage after few days. please don't only think benchmark. > Under streaming IO, the current get_scan_ratio() will get a percent[0] > that is (much) less than 1, so underflows to 0. > > It has the bad effect of completely disabling the scan of anon list, > which leads to OOM in Shaohua's test case. OTOH, it also has the good > side effect of keeping anon pages in memory and totally prevent swap > IO. > > Shaohua's patch improves the computation precision by computing nr[] > directly in get_scan_ratio(). This is good in general, however will > enable light scan of the anon list on streaming IO. In such case, percent[0] should be big. I think underflowing is not point. His test case is merely streaming io copy, why can't we drop tmpfs cached page? his /proc/meminfo describe his machine didn't have droppable file cache. so, big percent[1] value seems makes no sense. no? I'm not sure we need either below detection. I need more investigate. 1) detect no discardable file cache 2) detect streaming io on tmpfs (as regular file) -- 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