From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 0194D6B0026 for ; Tue, 17 May 2011 02:26:21 -0400 (EDT) Received: by qyk2 with SMTP id 2so2284818qyk.14 for ; Mon, 16 May 2011 23:26:17 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110517055204.GB24069@localhost> References: <20110512054631.GI6008@one.firstfloor.org> <20110514165346.GV6008@one.firstfloor.org> <20110514174333.GW6008@one.firstfloor.org> <20110515152747.GA25905@localhost> <20110517055204.GB24069@localhost> Date: Tue, 17 May 2011 15:26:17 +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 Tue, May 17, 2011 at 2:52 PM, Wu Fengguang wrot= e: > 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 wro= te: >> >> > 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 re= claim >> >> >> >> 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 >> > >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A02 * (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_NORETR= Y. >> 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 >> > =C2=A0(current readahead heuristic can somehow do this, and I have pat= ches >> > =C2=A0to 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 :) =C2=A0When you see RA page > allocations stealing high order pages, it may actually be reflecting > some more general order-0 steal order-N problem.. Agree. As I said to Andy, it's a general problem but RA has a possibility to reduce it while others don't have a any solution. :( --=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