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Date: Tue, 13 Dec 2011 20:45:46 -0800 From: Mike Waychison <mikew@...gle.com> To: Shaohua Li <shaohua.li@...el.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan.kim@...il.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Johannes Weiner <jweiner@...hat.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Hugh Dickens <hughd@...gle.com>, Greg Thelen <gthelen@...gle.com> Subject: Re: [PATCH] mm: Fix kswapd livelock on single core, no preempt kernel On Tue, Dec 13, 2011 at 8:36 PM, Mike Waychison <mikew@...gle.com> wrote: > On Tue, Dec 13, 2011 at 6:24 PM, Shaohua Li <shaohua.li@...el.com> 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. This 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. In turn, sleeping_prematurely() >>> will consistently return true and kswapd_try_to_sleep() to never invoke >>> schedule(). This 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. This 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? Actually, I don't see where sleeping_prematurely() would return false if any zone has ->all_unreclaimable set. In this case, the order was 0, so we return !all_zones_ok, which is false because !zone_watermark_ok_safe(ZONE_DMA32). > > 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 = 773 > /cloud/vmm/host/backend/perfmetric/node0/zone0/active_file : long long = 6 > /cloud/vmm/host/backend/perfmetric/node0/zone0/anon_pages : long long = 1,329 > /cloud/vmm/host/backend/perfmetric/node0/zone0/bounce : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone0/dirtied : long long = 4,425 > /cloud/vmm/host/backend/perfmetric/node0/zone0/file_dirty : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone0/file_mapped : long long = 5 > /cloud/vmm/host/backend/perfmetric/node0/zone0/file_pages : long long = 330 > /cloud/vmm/host/backend/perfmetric/node0/zone0/free_pages : long long = 2,018 > /cloud/vmm/host/backend/perfmetric/node0/zone0/inactive_anon : long long = 865 > /cloud/vmm/host/backend/perfmetric/node0/zone0/inactive_file : long long = 13 > /cloud/vmm/host/backend/perfmetric/node0/zone0/kernel_stack : long long = 10 > /cloud/vmm/host/backend/perfmetric/node0/zone0/mlock : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone0/pagetable : long long = 74 > /cloud/vmm/host/backend/perfmetric/node0/zone0/shmem : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone0/slab_reclaimable : long long = 54 > /cloud/vmm/host/backend/perfmetric/node0/zone0/slab_unreclaimable : > long long = 130 > /cloud/vmm/host/backend/perfmetric/node0/zone0/unevictable : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone0/writeback : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone0/written : long long = 47,184 > > /cloud/vmm/host/backend/perfmetric/node0/zone1/active_anon : long long = 359,251 > /cloud/vmm/host/backend/perfmetric/node0/zone1/active_file : long long = 67 > /cloud/vmm/host/backend/perfmetric/node0/zone1/anon_pages : long long = 441,180 > /cloud/vmm/host/backend/perfmetric/node0/zone1/bounce : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone1/dirtied : long long = 6,457,125 > /cloud/vmm/host/backend/perfmetric/node0/zone1/file_dirty : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone1/file_mapped : long long = 134 > /cloud/vmm/host/backend/perfmetric/node0/zone1/file_pages : long long = 38,090 > /cloud/vmm/host/backend/perfmetric/node0/zone1/free_pages : long long = 1,630 > /cloud/vmm/host/backend/perfmetric/node0/zone1/inactive_anon : long > long = 119,779 > /cloud/vmm/host/backend/perfmetric/node0/zone1/inactive_file : long long = 81 > /cloud/vmm/host/backend/perfmetric/node0/zone1/kernel_stack : long long = 173 > /cloud/vmm/host/backend/perfmetric/node0/zone1/mlock : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone1/pagetable : long long = 15,222 > /cloud/vmm/host/backend/perfmetric/node0/zone1/shmem : long long = 1 > /cloud/vmm/host/backend/perfmetric/node0/zone1/slab_reclaimable : long > long = 1,677 > /cloud/vmm/host/backend/perfmetric/node0/zone1/slab_unreclaimable : > long long = 7,152 > /cloud/vmm/host/backend/perfmetric/node0/zone1/unevictable : long long = 0 > /cloud/vmm/host/backend/perfmetric/node0/zone1/writeback : long long = 8 > /cloud/vmm/host/backend/perfmetric/node0/zone1/written : long long = 16,639,708 > > 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 == 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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