From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932395Ab3AJAS4 (ORCPT ); Wed, 9 Jan 2013 19:18:56 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:36046 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932206Ab3AJASz (ORCPT ); Wed, 9 Jan 2013 19:18:55 -0500 Date: Wed, 9 Jan 2013 16:18:54 -0800 From: Andrew Morton To: Minchan Kim Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Magenheimer , Sonny Rao , Bryan Freed , Hugh Dickins , Rik van Riel , Johannes Weiner Subject: Re: [PATCH 1/2] mm: prevent to add a page to swap if may_writepage is unset Message-Id: <20130109161854.67412dcc.akpm@linux-foundation.org> In-Reply-To: <1357712474-27595-2-git-send-email-minchan@kernel.org> References: <1357712474-27595-1-git-send-email-minchan@kernel.org> <1357712474-27595-2-git-send-email-minchan@kernel.org> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 9 Jan 2013 15:21:13 +0900 Minchan Kim wrote: > Recently, Luigi reported there are lots of free swap space when > OOM happens. It's easily reproduced on zram-over-swap, where > many instance of memory hogs are running and laptop_mode is enabled. > > Luigi reported there was no problem when he disabled laptop_mode. > The problem when I investigate problem is following as. > > try_to_free_pages disable may_writepage if laptop_mode is enabled. > shrink_page_list adds lots of anon pages in swap cache by > add_to_swap, which makes pages Dirty and rotate them to head of > inactive LRU without pageout. If it is repeated, inactive anon LRU > is full of Dirty and SwapCache pages. > > In case of that, isolate_lru_pages fails because it try to isolate > clean page due to may_writepage == 0. > > The may_writepage could be 1 only if total_scanned is higher than > writeback_threshold in do_try_to_free_pages but unfortunately, > VM can't isolate anon pages from inactive anon lru list by > above reason and we already reclaimed all file-backed pages. > So it ends up OOM killing. > > This patch prevents to add a page to swap cache unnecessary when > may_writepage is unset so anoymous lru list isn't full of > Dirty/Swapcache page. So VM can isolate pages from anon lru list, > which ends up setting may_writepage to 1 and could swap out > anon lru pages. When OOM triggers, I confirmed swap space was full. > > ... > > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -780,6 +780,8 @@ static unsigned long shrink_page_list(struct list_head *page_list, > if (PageAnon(page) && !PageSwapCache(page)) { > if (!(sc->gfp_mask & __GFP_IO)) > goto keep_locked; > + if (!sc->may_writepage) > + goto keep_locked; > if (!add_to_swap(page)) > goto activate_locked; > may_enter_fs = 1; I'm not really getting it, and the description is rather hard to follow :( We should be adding anon pages to swapcache even when laptop_mode is set. And we should be writing them to swap as well, then reclaiming them. The only thing laptop_mode shouild do is make the disk spin up less frequently - that doesn't mean "not at all"! So something seems screwed up here and the patch looks like a heavy-handed workaround. Why aren't these anon pages getting written out in laptop_mode?