From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx129.postini.com [74.125.245.129]) by kanga.kvack.org (Postfix) with SMTP id 791026B02AF for ; Tue, 13 Dec 2011 23:37:04 -0500 (EST) Received: by ggni2 with SMTP id i2so476418ggn.14 for ; Tue, 13 Dec 2011 20:37:03 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1323829490.22361.395.camel@sli10-conroe> References: <1323798271-1452-1-git-send-email-mikew@google.com> <1323829490.22361.395.camel@sli10-conroe> From: Mike Waychison Date: Tue, 13 Dec 2011 20:36:43 -0800 Message-ID: Subject: Re: [PATCH] mm: Fix kswapd livelock on single core, no preempt kernel Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Shaohua Li Cc: Andrew Morton , Mel Gorman , Minchan Kim , KAMEZAWA Hiroyuki , Johannes Weiner , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Hugh Dickens , Greg Thelen On Tue, Dec 13, 2011 at 6:24 PM, Shaohua Li wrote: > On Wed, 2011-12-14 at 01:44 +0800, Mike Waychison wrote: >> On a single core system with kernel preemption disabled, it is possible >> for the memory system to be so taxed that kswapd cannot make any forward >> progress. =A0This can happen when most of system memory is tied up as >> anonymous memory without swap enabled, causing kswapd to consistently >> fail to achieve its watermark goals. =A0In turn, sleeping_prematurely() >> will consistently return true and kswapd_try_to_sleep() to never invoke >> schedule(). =A0This causes the kswapd thread to stay on the CPU in >> perpetuity and keeps other threads from processing oom-kills to reclaim >> memory. >> >> The cond_resched() instance in balance_pgdat() is never called as the >> loop that iterates from DEF_PRIORITY down to 0 will always set >> all_zones_ok to true, and not set it to false once we've passed >> DEF_PRIORITY as zones that are marked ->all_unreclaimable are not >> considered in the "all_zones_ok" evaluation. >> >> This change modifies kswapd_try_to_sleep to ensure that we enter >> scheduler at least once per invocation if needed. =A0This allows kswapd = to >> get off the CPU and allows other threads to die off from the OOM killer >> (freeing memory that is otherwise unavailable in the process). > your description suggests zones with all_unreclaimable set. but in this > case sleeping_prematurely() will return false instead of true, kswapd > will do sleep then. is there anything I missed? Debugging this, I didn't get a dump from oom-kill as it never ran (until I binary patched in a cond_resched() into live hung machines -- this reproduced in a VM). I was however able to capture the following data while it was hung: /cloud/vmm/host/backend/perfmetric/node0/zone0/active_anon : long long =3D = 773 /cloud/vmm/host/backend/perfmetric/node0/zone0/active_file : long long =3D = 6 /cloud/vmm/host/backend/perfmetric/node0/zone0/anon_pages : long long =3D 1= ,329 /cloud/vmm/host/backend/perfmetric/node0/zone0/bounce : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone0/dirtied : long long =3D 4,42= 5 /cloud/vmm/host/backend/perfmetric/node0/zone0/file_dirty : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone0/file_mapped : long long =3D = 5 /cloud/vmm/host/backend/perfmetric/node0/zone0/file_pages : long long =3D 3= 30 /cloud/vmm/host/backend/perfmetric/node0/zone0/free_pages : long long =3D 2= ,018 /cloud/vmm/host/backend/perfmetric/node0/zone0/inactive_anon : long long = =3D 865 /cloud/vmm/host/backend/perfmetric/node0/zone0/inactive_file : long long = =3D 13 /cloud/vmm/host/backend/perfmetric/node0/zone0/kernel_stack : long long =3D= 10 /cloud/vmm/host/backend/perfmetric/node0/zone0/mlock : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone0/pagetable : long long =3D 74 /cloud/vmm/host/backend/perfmetric/node0/zone0/shmem : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone0/slab_reclaimable : long long= =3D 54 /cloud/vmm/host/backend/perfmetric/node0/zone0/slab_unreclaimable : long long =3D 130 /cloud/vmm/host/backend/perfmetric/node0/zone0/unevictable : long long =3D = 0 /cloud/vmm/host/backend/perfmetric/node0/zone0/writeback : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone0/written : long long =3D 47,1= 84 /cloud/vmm/host/backend/perfmetric/node0/zone1/active_anon : long long =3D = 359,251 /cloud/vmm/host/backend/perfmetric/node0/zone1/active_file : long long =3D = 67 /cloud/vmm/host/backend/perfmetric/node0/zone1/anon_pages : long long =3D 4= 41,180 /cloud/vmm/host/backend/perfmetric/node0/zone1/bounce : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone1/dirtied : long long =3D 6,45= 7,125 /cloud/vmm/host/backend/perfmetric/node0/zone1/file_dirty : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone1/file_mapped : long long =3D = 134 /cloud/vmm/host/backend/perfmetric/node0/zone1/file_pages : long long =3D 3= 8,090 /cloud/vmm/host/backend/perfmetric/node0/zone1/free_pages : long long =3D 1= ,630 /cloud/vmm/host/backend/perfmetric/node0/zone1/inactive_anon : long long =3D 119,779 /cloud/vmm/host/backend/perfmetric/node0/zone1/inactive_file : long long = =3D 81 /cloud/vmm/host/backend/perfmetric/node0/zone1/kernel_stack : long long =3D= 173 /cloud/vmm/host/backend/perfmetric/node0/zone1/mlock : long long =3D 0 /cloud/vmm/host/backend/perfmetric/node0/zone1/pagetable : long long =3D 15= ,222 /cloud/vmm/host/backend/perfmetric/node0/zone1/shmem : long long =3D 1 /cloud/vmm/host/backend/perfmetric/node0/zone1/slab_reclaimable : long long =3D 1,677 /cloud/vmm/host/backend/perfmetric/node0/zone1/slab_unreclaimable : long long =3D 7,152 /cloud/vmm/host/backend/perfmetric/node0/zone1/unevictable : long long =3D = 0 /cloud/vmm/host/backend/perfmetric/node0/zone1/writeback : long long =3D 8 /cloud/vmm/host/backend/perfmetric/node0/zone1/written : long long =3D 16,6= 39,708 These value were static while the machine was hung up in kswapd. I unfortunately don't have the low/min/max or lowmem watermarks handy. >>From stepping through with gdb, I was able to determine that ZONE_DMA32 would fail zone_watermark_ok_safe(), causing a scan up to end_zone =3D=3D 1. If memory serves, it would not get the ->all_unreclaimable flag. I didn't get the chance to root cause this internal inconsistency though. FYI, this was seen with a 2.6.39-based kernel with no-numa, no-memcg and swap-enabled. If I get the chance, I can reproduce and look at this closer to try and root cause why zone_reclaimable() would return true, but I won't be able to do that until after the holidays -- sometime in January. -- 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