From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 491266B007B for ; Tue, 14 Sep 2010 23:47:41 -0400 (EDT) Date: Wed, 15 Sep 2010 11:47:35 +0800 From: Wu Fengguang Subject: Re: Deadlock possibly caused by too_many_isolated. Message-ID: <20100915034734.GA12264@localhost> References: <20100915091118.3dbdc961@notabene> <4C90139A.1080809@redhat.com> <20100915122334.3fa7b35f@notabene> <20100915023735.GA9175@localhost> <20100915025454.GA10230@localhost> <20100915030640.GA11141@localhost> <20100915131735.08899288@notabene> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100915131735.08899288@notabene> Sender: owner-linux-mm@kvack.org To: Neil Brown Cc: Rik van Riel , Andrew Morton , KOSAKI Motohiro , KAMEZAWA Hiroyuki , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" List-ID: On Wed, Sep 15, 2010 at 11:17:35AM +0800, Neil Brown wrote: > On Wed, 15 Sep 2010 11:06:40 +0800 > Wu Fengguang wrote: > > > On Wed, Sep 15, 2010 at 10:54:54AM +0800, Wu Fengguang wrote: > > > On Wed, Sep 15, 2010 at 10:37:35AM +0800, Wu Fengguang wrote: > > > > On Wed, Sep 15, 2010 at 10:23:34AM +0800, Neil Brown wrote: > > > > > On Tue, 14 Sep 2010 20:30:18 -0400 > > > > > Rik van Riel wrote: > > > > > > > > > > > On 09/14/2010 07:11 PM, Neil Brown wrote: > > > > > > > > > > > > > Index: linux-2.6.32-SLE11-SP1/mm/vmscan.c > > > > > > > =================================================================== > > > > > > > --- linux-2.6.32-SLE11-SP1.orig/mm/vmscan.c 2010-09-15 08:37:32.000000000 +1000 > > > > > > > +++ linux-2.6.32-SLE11-SP1/mm/vmscan.c 2010-09-15 08:38:57.000000000 +1000 > > > > > > > @@ -1106,6 +1106,11 @@ static unsigned long shrink_inactive_lis > > > > > > > /* We are about to die and free our memory. Return now. */ > > > > > > > if (fatal_signal_pending(current)) > > > > > > > return SWAP_CLUSTER_MAX; > > > > > > > + if (!(sc->gfp_mask& __GFP_IO)) > > > > > > > + /* Not allowed to do IO, so mustn't wait > > > > > > > + * on processes that might try to > > > > > > > + */ > > > > > > > + return SWAP_CLUSTER_MAX; > > > > > > > } > > > > > > > > > > > > > > /* > > > > > > > > > > > > Close. We must also be sure that processes without __GFP_FS > > > > > > set in their gfp_mask do not wait on processes that do have > > > > > > __GFP_FS set. > > > > > > > > > > > > Considering how many times we've run into a bug like this, > > > > > > I'm kicking myself for not having thought of it :( > > > > > > > > > > > > > > > > So maybe this? I've added the test for __GFP_FS, and moved the test before > > > > > the congestion_wait on the basis that we really want to get back up the stack > > > > > and try the mempool ASAP. > > > > > > > > The patch may well fail the !__GFP_IO page allocation and then > > > > quickly exhaust the mempool. > > > > > > > > Another approach may to let too_many_isolated() use much higher > > > > thresholds for !__GFP_IO/FS and lower ones for __GFP_IO/FS. ie. to > > > > allow at least nr2 NOIO/FS tasks to be blocked independent of the > > > > IO/FS ones. Since NOIO vmscans typically completes fast, it will then > > > > very hard to accumulate enough NOIO processes to be actually blocked. > > > > > > > > > > > > IO/FS tasks NOIO/FS tasks full > > > > block here block here LRU size > > > > |-----------------|--------------------------|-----------------------| > > > > | nr1 | nr2 | > > > > > > How about this fix? We may need very high threshold for NOIO/NOFS to > > > prevent possible regressions. > > > > Plus __GFP_WAIT.. > > > > --- > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 225a759..6a896eb 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -1135,6 +1135,7 @@ static int too_many_isolated(struct zone *zone, int file, > > struct scan_control *sc) > > { > > unsigned long inactive, isolated; > > + int ratio; > > > > if (current_is_kswapd()) > > return 0; > > @@ -1150,7 +1151,15 @@ static int too_many_isolated(struct zone *zone, int file, > > isolated = zone_page_state(zone, NR_ISOLATED_ANON); > > } > > > > - return isolated > inactive; > > + ratio = 1; > > + if (!(sc->gfp_mask & (__GFP_FS))) > > + ratio <<= 1; > > + if (!(sc->gfp_mask & (__GFP_IO))) > > + ratio <<= 1; > > + if (!(sc->gfp_mask & (__GFP_WAIT))) > > + ratio <<= 1; > > + > > + return isolated > inactive * ratio; > > } > > > > /* > > > Are you suggesting this instead of my patch, or as well as my patch? Your patch surely breaks the deadlock, however might reintroduce the old problem too_many_isolated() tried to address.. > Because while I think it sounds like a good idea I don't think it actually > removes the chance of a deadlock, just makes it a lot less likely. > So I think your patch combined with my patch would be a good total solution. Deadlock means IO/FS tasks (blocked on FS lock) blocking the NOIO/FS tasks? I think raising the threshold for NOIO/FS would be sufficient to break the deadlock: The NOIO/FS tasks will be blocked simply because there are so many NOIO/FS tasks competing with each other. They do not inherently depend on the release of FS locks to proceed. The too_many_isolated() was introduced initially to prevent OOM for some fork-bomb workload, where no IO is involved (so no FS locks). If removing the congestion wait for NOIO/FS tasks, the OOM may raise again for the fork-bomb workload. So I'd suggest to use sufficient high threshold for NOIO/FS, but still limit the number of concurrent NOIO/FS allocations. Thanks, Fengguang -- 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