Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754782Ab1EXIgU (ORCPT ); Tue, 24 May 2011 04:36:20 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:48866 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754560Ab1EXIgR (ORCPT ); Tue, 24 May 2011 04:36:17 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Message-ID: <4DDB6DF6.2050700@jp.fujitsu.com> Date: Tue, 24 May 2011 17:36:06 +0900 From: KOSAKI Motohiro User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; ja; rv:1.9.2.17) Gecko/20110414 Lightning/1.0b2 Thunderbird/3.1.10 MIME-Version: 1.0 To: mgorman@suse.de CC: minchan.kim@gmail.com, abarry@cray.com, akpm@linux-foundation.org, linux-mm@kvack.org, riel@redhat.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org Subject: Re: Unending loop in __alloc_pages_slowpath following OOM-kill; rfc: patch. References: <4DCDA347.9080207@cray.com> <4DD2991B.5040707@cray.com> <20110520164924.GB2386@barrios-desktop> <4DDB3A1E.6090206@jp.fujitsu.com> <20110524083008.GA5279@suse.de> In-Reply-To: <20110524083008.GA5279@suse.de> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4758 Lines: 115 (2011/05/24 17:30), Mel Gorman wrote: > On Tue, May 24, 2011 at 01:54:54PM +0900, KOSAKI Motohiro wrote: >>> >From 8bd3f16736548375238161d1bd85f7d7c381031f Mon Sep 17 00:00:00 2001 >>> From: Minchan Kim >>> Date: Sat, 21 May 2011 01:37:41 +0900 >>> Subject: [PATCH] Prevent unending loop in __alloc_pages_slowpath >>> >>> From: Andrew Barry >>> >>> I believe I found a problem in __alloc_pages_slowpath, which allows a process to >>> get stuck endlessly looping, even when lots of memory is available. >>> >>> Running an I/O and memory intensive stress-test I see a 0-order page allocation >>> with __GFP_IO and __GFP_WAIT, running on a system with very little free memory. >>> Right about the same time that the stress-test gets killed by the OOM-killer, >>> the utility trying to allocate memory gets stuck in __alloc_pages_slowpath even >>> though most of the systems memory was freed by the oom-kill of the stress-test. >>> >>> The utility ends up looping from the rebalance label down through the >>> wait_iff_congested continiously. Because order=0, __alloc_pages_direct_compact >>> skips the call to get_page_from_freelist. Because all of the reclaimable memory >>> on the system has already been reclaimed, __alloc_pages_direct_reclaim skips the >>> call to get_page_from_freelist. Since there is no __GFP_FS flag, the block with >>> __alloc_pages_may_oom is skipped. The loop hits the wait_iff_congested, then >>> jumps back to rebalance without ever trying to get_page_from_freelist. This loop >>> repeats infinitely. >>> >>> The test case is pretty pathological. Running a mix of I/O stress-tests that do >>> a lot of fork() and consume all of the system memory, I can pretty reliably hit >>> this on 600 nodes, in about 12 hours. 32GB/node. >>> >>> Signed-off-by: Andrew Barry >>> Reviewed-by: Minchan Kim >>> Cc: Mel Gorman >>> --- >>> mm/page_alloc.c | 2 +- >>> 1 files changed, 1 insertions(+), 1 deletions(-) >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 3f8bce2..e78b324 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -2064,6 +2064,7 @@ restart: >>> first_zones_zonelist(zonelist, high_zoneidx, NULL, >>> &preferred_zone); >>> >>> +rebalance: >>> /* This is the last chance, in general, before the goto nopage. */ >>> page = get_page_from_freelist(gfp_mask, nodemask, order, zonelist, >>> high_zoneidx, alloc_flags & ~ALLOC_NO_WATERMARKS, >>> @@ -2071,7 +2072,6 @@ restart: >>> if (page) >>> goto got_pg; >>> >>> -rebalance: >>> /* Allocate without watermarks if the context allows */ >>> if (alloc_flags & ALLOC_NO_WATERMARKS) { >>> page = __alloc_pages_high_priority(gfp_mask, order, >> >> I'm sorry I missed this thread long time. >> >> In this case, I think we should call drain_all_pages(). > > Why? Otherwise, we don't have good PCP dropping trigger. Big machine might have big pcp cache. > If the direct reclaimer failed to reclaim any pages on its own, the call > to get_page_from_freelist() is going to be useless and there is > no guarantee that any other CPU managed to reclaim pages either. All > this ends up doing is sending in IPI which if it's very lucky will take > a page from another CPUs free list. It's no matter. because did_some_progress==0 mean vmscan failed to reclaim any pages and reach priority==0. Thus, it obviously slow path. > >> then following >> patch is better. >> However I also think your patch is valuable. because while the task is >> sleeping in wait_iff_congested(), an another task may free some pages. >> thus, rebalance path should try to get free pages. iow, you makes sense. >> >> So, I'd like to propose to merge both your and my patch. >> >> Thanks. >> >> >> From 2e77784668f6ca53d88ecb46aa6b99d9d0f33ffa Mon Sep 17 00:00:00 2001 >> From: KOSAKI Motohiro >> Date: Tue, 24 May 2011 13:41:57 +0900 >> Subject: [PATCH] vmscan: remove painful micro optimization >> >> Currently, __alloc_pages_direct_reclaim() call get_page_from_freelist() >> only if try_to_free_pages() return !0. >> >> It's no necessary micro optimization becauase "return 0" mean vmscan reached >> priority 0 and didn't get any pages, iow, it's really slow path. But also it >> has bad side effect. If we don't call drain_all_pages(), we have a chance to >> get infinite loop. >> > > With the "rebalance" patch, where is the infinite loop? I wrote the above. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/