Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752206Ab1EQFwK (ORCPT ); Tue, 17 May 2011 01:52:10 -0400 Received: from mga01.intel.com ([192.55.52.88]:12397 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751841Ab1EQFwG (ORCPT ); Tue, 17 May 2011 01:52:06 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,223,1304319600"; d="scan'208";a="3161184" Date: Tue, 17 May 2011 13:52:04 +0800 From: Wu Fengguang To: Minchan Kim Cc: Andi Kleen , "linux-mm@kvack.org" , Andrew Lutomirski , LKML Subject: Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux) Message-ID: <20110517055204.GB24069@localhost> References: <20110512054631.GI6008@one.firstfloor.org> <20110514165346.GV6008@one.firstfloor.org> <20110514174333.GW6008@one.firstfloor.org> <20110515152747.GA25905@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2777 Lines: 70 On Mon, May 16, 2011 at 07:40:42AM +0900, Minchan Kim wrote: > On Mon, May 16, 2011 at 12:27 AM, Wu Fengguang wrote: > > On Sun, May 15, 2011 at 09:37:58AM +0800, Minchan Kim wrote: > >> On Sun, May 15, 2011 at 2:43 AM, Andi Kleen wrote: > >> > Copying back linux-mm. > >> > > >> >> Recently, we added following patch. > >> >> https://lkml.org/lkml/2011/4/26/129 > >> >> If it's a culprit, the patch should solve the problem. > >> > > >> > It would be probably better to not do the allocations at all under > >> > memory pressure.  Even if the RA allocation doesn't go into reclaim > >> > >> Fair enough. > >> I think we can do it easily now. > >> If page_cache_alloc_readahead(ie, GFP_NORETRY) is fail, we can adjust > >> RA window size or turn off a while. The point is that we can use the > >> fail of __do_page_cache_readahead as sign of memory pressure. > >> Wu, What do you think? > > > > No, disabling readahead can hardly help. > > I don't mean we have to disable RA. > As I said, the point is that we can use __GFP_NORETRY alloc fail as > _sign_ of memory pressure. I see. > > > > The sequential readahead memory consumption can be estimated by > > > >                2 * (number of concurrent read streams) * (readahead window size) > > > > And you can double that when there are two level of readaheads. > > > > Since there are hardly any concurrent read streams in Andy's case, > > the readahead memory consumption will be ignorable. > > > > Typically readahead thrashing will happen long before excessive > > GFP_NORETRY failures, so the reasonable solutions are to > > If it is, RA thrashing could be better sign than failure of __GFP_NORETRY. > If we can do it easily, I don't object it. :) Yeah, the RA thrashing is much better sign because it not only happens long before normal __GFP_NORETRY failures, but also offers hint on how tight memory pressure it is. We can then shrink the readahead window adaptively to the available page cache memory :) > > > > - shrink readahead window on readahead thrashing > >  (current readahead heuristic can somehow do this, and I have patches > >  to further improve it) > > Good to hear. :) > I don't want RA steals high order page in memory pressure. More often than not it won't be RA's fault :) When you see RA page allocations stealing high order pages, it may actually be reflecting some more general order-0 steal order-N problem.. > My patch and shrinking RA window helps this case. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/