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 ESMTP id 308DF6B002D for ; Tue, 25 Oct 2011 03:51:29 -0400 (EDT) Received: from wpaz37.hot.corp.google.com (wpaz37.hot.corp.google.com [172.24.198.101]) by smtp-out.google.com with ESMTP id p9P7pLXt004161 for ; Tue, 25 Oct 2011 00:51:23 -0700 Received: from vcbfo14 (vcbfo14.prod.google.com [10.220.205.14]) by wpaz37.hot.corp.google.com with ESMTP id p9P7nW9X027567 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for ; Tue, 25 Oct 2011 00:51:20 -0700 Received: by vcbfo14 with SMTP id fo14so321378vcb.4 for ; Tue, 25 Oct 2011 00:51:20 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1319524789-22818-1-git-send-email-ccross@android.com> Date: Tue, 25 Oct 2011 00:51:19 -0700 Message-ID: Subject: Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations From: Colin Cross Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Pekka Enberg Cc: linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman , KAMEZAWA Hiroyuki , Andrea Arcangeli , David Rientjes , linux-mm@kvack.org On Tue, Oct 25, 2011 at 12:40 AM, Pekka Enberg wro= te: > On Tue, Oct 25, 2011 at 9:39 AM, Colin Cross wrote: >> Under the following conditions, __alloc_pages_slowpath can loop >> forever: >> gfp_mask & __GFP_WAIT is true >> gfp_mask & __GFP_FS is false >> reclaim and compaction make no progress >> order <=3D PAGE_ALLOC_COSTLY_ORDER >> >> These conditions happen very often during suspend and resume, >> when pm_restrict_gfp_mask() effectively converts all GFP_KERNEL >> allocations into __GFP_WAIT. > > Why does it do that? Why don't we fix the gfp mask instead? It disables __GFP_IO and __GFP_FS because the IO drivers may be suspended. >> The oom killer is not run because gfp_mask & __GFP_FS is false, >> but should_alloc_retry will always return true when order is less >> than PAGE_ALLOC_COSTLY_ORDER. >> >> Fix __alloc_pages_slowpath to skip retrying when oom killer is >> not allowed by the GFP flags, the same way it would skip if the >> oom killer was allowed but disabled. >> >> Signed-off-by: Colin Cross >> --- >> >> An alternative patch would add a did_some_progress argument to >> __alloc_pages_may_oom, and remove the checks in >> __alloc_pages_slowpath that require knowledge of when >> __alloc_pages_may_oom chooses to run out_of_memory. If >> did_some_progress was still zero, it would goto nopage whether >> or not __alloc_pages_may_oom was actually called. >> >> =A0mm/page_alloc.c | =A0 =A04 ++++ >> =A01 files changed, 4 insertions(+), 0 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index fef8dc3..dcd99b3 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -2193,6 +2193,10 @@ rebalance: >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto restart; >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 } else { >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* If we aren't going to t= ry the OOM killer, give up */ >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!(gfp_mask & __GFP_NOF= AIL)) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto nopag= e; >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} >> =A0 =A0 =A0 =A0} > > I don't quite understand how __GFP_WAIT is involved here. Which path > is causing the infinite loop? GFP_KERNEL is __GFP_WAIT | __GFP_IO | __GFP_FS. Once driver suspend has started, gfp_allowed_mask is ~(__GFP_IO | GFP_FS), so any call to __alloc_pages_nodemask(GFP_KERNEL, ...) gets masked to effectively __alloc_pages_nodemask(__GFP_WAIT, ...). The loop is in __alloc_pages_slowpath, from the rebalance label to should_alloc_retry. Under the conditions I listed in the commit message, there is no path to the nopage label, because all the relevant "goto nopage" lines that would normally allow a GFP_KERNEL allocation to fail are inside a check for __GFP_FS. Modifying the gfp_allowed_mask would not completely fix the issue, a GFP_NOIO allocation can meet the conditions outside of suspend. gfp_allowed_mask just makes the issue more likely, by converting GFP_KERNEL into GFP_NOIO. -- 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