From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753542AbaFWLaA (ORCPT ); Mon, 23 Jun 2014 07:30:00 -0400 Received: from cantor2.suse.de ([195.135.220.15]:44001 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752581AbaFWL37 (ORCPT ); Mon, 23 Jun 2014 07:29:59 -0400 Date: Mon, 23 Jun 2014 13:29:55 +0200 From: Michal Hocko To: Xishi Qiu Cc: Rafael Aquini , Andrew Morton , Wanpeng Li , Greg Kroah-Hartman , Peter Zijlstra , Rik van Riel , Johannes Weiner , Linux MM , LKML , Li Zefan Subject: Re: [PATCH 0/8] mm: add page cache limit and reclaim feature Message-ID: <20140623112955.GL9743@dhcp22.suse.cz> References: <539EB7D6.8070401@huawei.com> <20140616111422.GA16915@dhcp22.suse.cz> <20140616125040.GA29993@optiplex.redhat.com> <539F9B6C.1080802@huawei.com> <53A3E948.5020701@huawei.com> <20140620153212.GD23115@dhcp22.suse.cz> <53A78B7C.1050302@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53A78B7C.1050302@huawei.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 23-06-14 10:05:48, Xishi Qiu wrote: > On 2014/6/20 23:32, Michal Hocko wrote: > > > On Fri 20-06-14 15:56:56, Xishi Qiu wrote: > >> On 2014/6/17 9:35, Xishi Qiu wrote: > >> > >>> On 2014/6/16 20:50, Rafael Aquini wrote: > >>> > >>>> On Mon, Jun 16, 2014 at 01:14:22PM +0200, Michal Hocko wrote: > >>>>> On Mon 16-06-14 17:24:38, Xishi Qiu wrote: > >>>>>> When system(e.g. smart phone) running for a long time, the cache often takes > >>>>>> a large memory, maybe the free memory is less than 50M, then OOM will happen > >>>>>> if APP allocate a large order pages suddenly and memory reclaim too slowly. > >>>>> > >>>>> Have you ever seen this to happen? Page cache should be easy to reclaim and > >>>>> if there is too mach dirty memory then you should be able to tune the > >>>>> amount by dirty_bytes/ratio knob. If the page allocator falls back to > >>>>> OOM and there is a lot of page cache then I would call it a bug. I do > >>>>> not think that limiting the amount of the page cache globally makes > >>>>> sense. There are Unix systems which offer this feature but I think it is > >>>>> a bad interface which only papers over the reclaim inefficiency or lack > >>>>> of other isolations between loads. > >>>>> > >>>> +1 > >>>> > >>>> It would be good if you could show some numbers that serve as evidence > >>>> of your theory on "excessive" pagecache acting as a trigger to your > >>>> observed OOMs. I'm assuming, by your 'e.g', you're running a swapless > >>>> system, so I would think your system OOMs are due to inability to > >>>> reclaim anon memory, instead of pagecache. > >>>> > >> > >> I asked some colleagues, when the cache takes a large memory, it will not > >> trigger OOM, but performance regression. > >> > >> It is because that business process do IO high frequency, and this will > >> increase page cache. When there is not enough memory, page cache will > >> be reclaimed first, then alloc a new page, and add it to page cache. This > >> often takes too much time, and causes performance regression. > > > > I cannot say I would understand the problem you are describing. So the > > page cache eats the most of the memory and that increases allocation > > latency for new page cache? Is it because of the direct reclaim? > > Yes, allocation latency causes performance regression. This doesn't make much sense to me. So you have a problem with latency caused by direct reclaim so you add a new way of direct page cache reclaim. > A user process produces page cache frequently, so free memory is not > enough after running a long time. Slow path takes much more time because > direct reclaim. And kswapd will reclaim memory too, but not much. Thus it > always triggers slow path. this will cause performance regression. If I were you I would focus on why the reclaim doesn't catch up with the page cache users. The mechanism you are proposing in unacceptable. -- Michal Hocko SUSE Labs