From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 7B1946B002D for ; Tue, 25 Oct 2011 04:08:15 -0400 (EDT) Received: by vcbfk1 with SMTP id fk1so235225vcb.14 for ; Tue, 25 Oct 2011 01:08:13 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1319524789-22818-1-git-send-email-ccross@android.com> Date: Tue, 25 Oct 2011 11:08:13 +0300 Message-ID: Subject: Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations From: Pekka Enberg Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Colin Cross Cc: linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman , KAMEZAWA Hiroyuki , Andrea Arcangeli , David Rientjes , linux-mm@kvack.org Hi Colin, 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. On Tue, Oct 25, 2011 at 12:40 AM, Pekka Enberg wro= te: >> Why does it do that? Why don't we fix the gfp mask instead? On Tue, Oct 25, 2011 at 10:51 AM, Colin Cross wrote: > It disables __GFP_IO and __GFP_FS because the IO drivers may be suspended= . Sure but why doesn't it clear __GFP_WAIT too? >>> 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 = try the OOM killer, give up */ >>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!(gfp_mask & __GFP_NO= FAIL)) >>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto nopa= ge; >>> =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. =A0Once 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. =A0Under 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. Right. Please include that information in the changelog. > 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. Why would anyone want to combine __GFP_WAIT, __GFP_NOFAIL and !__GFP_IO on purpose? What is it useful for? As for your patch: Acked-by: Pekka Enberg but I'd love to hear why we shouldn't also fix the suspend gfp mask to clear __GFP_WAIT and add a WARN_ON_ONCE to your new code path. Pekka -- 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