From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751727AbcGMNUY (ORCPT ); Wed, 13 Jul 2016 09:20:24 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:27821 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750963AbcGMNUO (ORCPT ); Wed, 13 Jul 2016 09:20:14 -0400 Subject: Re: System freezes after OOM To: Mikulas Patocka , Michal Hocko References: <57837CEE.1010609@redhat.com> <9be09452-de7f-d8be-fd5d-4a80d1cd1ba3@redhat.com> <20160712064905.GA14586@dhcp22.suse.cz> Cc: Ondrej Kozina , Jerome Marchand , Stanislav Kozina , linux-mm@kvack.org, linux-kernel@vger.kernel.org From: Tetsuo Handa Message-ID: <2d5e1f84-e886-7b98-cb11-170d7104fd13@I-love.SAKURA.ne.jp> Date: Wed, 13 Jul 2016 22:19:23 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Tue, 12 Jul 2016, Michal Hocko wrote: > >> On Mon 11-07-16 11:43:02, Mikulas Patocka wrote: >> [...] >>> The general problem is that the memory allocator does 16 retries to >>> allocate a page and then triggers the OOM killer (and it doesn't take into >>> account how much swap space is free or how many dirty pages were really >>> swapped out while it waited). >> >> Well, that is not how it works exactly. We retry as long as there is a >> reclaim progress (at least one page freed) back off only if the >> reclaimable memory can exceed watermks which is scaled down in 16 >> retries. The overal size of free swap is not really that important if we >> cannot swap out like here due to complete memory reserves depletion: >> https://okozina.fedorapeople.org/bugs/swap_on_dmcrypt/vmlog-1462458369-00000/sample-00011/dmesg: >> [ 90.491276] Node 0 DMA free:0kB min:60kB low:72kB high:84kB active_anon:4096kB inactive_anon:4636kB active_file:212kB inactive_file:280kB unevictable:488kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlocked:488kB dirty:276kB writeback:4636kB mapped:476kB shmem:12kB slab_reclaimable:204kB slab_unreclaimable:4700kB kernel_stack:48kB pagetables:120kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:61132 all_unreclaimable? yes >> [ 90.491283] lowmem_reserve[]: 0 977 977 977 >> [ 90.491286] Node 0 DMA32 free:0kB min:3828kB low:4824kB high:5820kB active_anon:423820kB inactive_anon:424916kB active_file:17996kB inactive_file:21800kB unevictable:20724kB isolated(anon):384kB isolated(file):0kB present:1032184kB managed:1001260kB mlocked:20724kB dirty:25236kB writeback:49972kB mapped:23076kB shmem:1364kB slab_reclaimable:13796kB slab_unreclaimable:43008kB kernel_stack:2816kB pagetables:7320kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:5635400 all_unreclaimable? yes >> >> Look at the amount of free memory. It is completely depleted. So it >> smells like a process which has access to memory reserves has consumed >> all of it. I suspect a __GFP_MEMALLOC resp. PF_MEMALLOC from softirq >> context user which went off the leash. > > It is caused by the commit f9054c70d28bc214b2857cf8db8269f4f45a5e23. Prior > to this commit, mempool allocations set __GFP_NOMEMALLOC, so they never > exhausted reserved memory. With this commit, mempool allocations drop > __GFP_NOMEMALLOC, so they can dig deeper (if the process has PF_MEMALLOC, > they can bypass all limits). I wonder whether commit f9054c70d28bc214 ("mm, mempool: only set __GFP_NOMEMALLOC if there are free elements") is doing correct thing. It says If an oom killed thread calls mempool_alloc(), it is possible that it'll loop forever if there are no elements on the freelist since __GFP_NOMEMALLOC prevents it from accessing needed memory reserves in oom conditions. but we can allow mempool_alloc(__GFP_NOMEMALLOC) requests to access memory reserves via below change, can't we? The purpose of allowing ALLOC_NO_WATERMARKS via TIF_MEMDIE is to make sure current allocation request does not to loop forever inside the page allocator, isn't it? Why we need to allow mempool_alloc(__GFP_NOMEMALLOC) requests to use ALLOC_NO_WATERMARKS when TIF_MEMDIE is not set? diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6903b69..e4e3700 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3439,14 +3439,14 @@ gfp_to_alloc_flags(gfp_t gfp_mask) } else if (unlikely(rt_task(current)) && !in_interrupt()) alloc_flags |= ALLOC_HARDER; - if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { + if (!in_interrupt() && unlikely(test_thread_flag(TIF_MEMDIE))) + alloc_flags |= ALLOC_NO_WATERMARKS; + else if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { if (gfp_mask & __GFP_MEMALLOC) alloc_flags |= ALLOC_NO_WATERMARKS; else if (in_serving_softirq() && (current->flags & PF_MEMALLOC)) alloc_flags |= ALLOC_NO_WATERMARKS; - else if (!in_interrupt() && - ((current->flags & PF_MEMALLOC) || - unlikely(test_thread_flag(TIF_MEMDIE)))) + else if (!in_interrupt() && (current->flags & PF_MEMALLOC)) alloc_flags |= ALLOC_NO_WATERMARKS; } #ifdef CONFIG_CMA