From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id C2A0A6B0022 for ; Sun, 15 May 2011 18:40:44 -0400 (EDT) Received: by qyk30 with SMTP id 30so2834967qyk.14 for ; Sun, 15 May 2011 15:40:43 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110515152747.GA25905@localhost> References: <20110512054631.GI6008@one.firstfloor.org> <20110514165346.GV6008@one.firstfloor.org> <20110514174333.GW6008@one.firstfloor.org> <20110515152747.GA25905@localhost> Date: Mon, 16 May 2011 07:40:42 +0900 Message-ID: Subject: Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux) From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Wu Fengguang Cc: Andi Kleen , "linux-mm@kvack.org" , Andrew Lutomirski , LKML On Mon, May 16, 2011 at 12:27 AM, Wu Fengguang wro= te: > 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. =C2=A0Even if the RA allocation doesn't go into recla= im >> >> 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. > > The sequential readahead memory consumption can be estimated by > > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A02 * (number of con= current 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. :) > > - shrink readahead window on readahead thrashing > =C2=A0(current readahead heuristic can somehow do this, and I have patche= s > =C2=A0to further improve it) Good to hear. :) I don't want RA steals high order page in memory pressure. My patch and shrinking RA window helps this case. --=20 Kind regards, Minchan Kim -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org