From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 22 Apr 2007 23:39:36 -0700 From: Andrew Morton Subject: Re: [PATCH 10/10] mm: per device dirty threshold Message-Id: <20070422233936.97d78677.akpm@linux-foundation.org> In-Reply-To: References: <20070420155154.898600123@chello.nl> <20070420155503.608300342@chello.nl> <20070421025532.916b1e2e.akpm@linux-foundation.org> <20070421035444.f7a42fad.akpm@linux-foundation.org> <1177308889.26937.1.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Miklos Szeredi Cc: a.p.zijlstra@chello.nl, linux-mm@kvack.org, linux-kernel@vger.kernel.org, neilb@suse.de, dgc@sgi.com, tomoki.sekiyama.qu@hitachi.com, nikita@clusterfs.com, trond.myklebust@fys.uio.no, yingchao.zhou@gmail.com List-ID: On Mon, 23 Apr 2007 08:29:59 +0200 Miklos Szeredi wrote: > > > What about swapout? That can increase the number of writeback pages, > > > without decreasing the number of dirty pages, no? > > > > Could we not solve that by enabling cap_account_writeback on > > swapper_space, and thereby account swap writeback pages. Then the VM > > knows it has outstanding IO and need not panic. > > Hmm, I'm not sure that would be right, because then those writeback > pages would be accounted twice: once for swapper_space, and once for > the real device. > > So there's a condition, when lots of anonymous pages are turned into > swap-cache writeback pages, and we should somehow throttle this, because > > >>> This means that all memory is pinned and unreclaimable and the VM gets > >>> upset and goes oom. > > although, it's not quite clear in my mind, how the VM gets upset about > this. I've been scratching my head on and off for a couple of days over this. We've traditionally had reclaim problems when there's a huge amount of dirty MAP_SHARED data, which the VM didn't know was dirty. It's the old "map a file which is the same size as physical memory and write to it all" stresstest. But we do not have such problems with anonymous memory, and I'm darned if I can remember why :( -- 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