[PATCH] mm,vmscan: Use accurate values for zone_reclaimable() checks
From: Tetsuo Handa
Date: Wed Oct 21 2015 - 08:26:30 EST
>From 0c50792dfa6396453c89c71351a7458b94d3e881 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Wed, 21 Oct 2015 21:15:30 +0900
Subject: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable() checks
Since "struct zone"->vm_stat[] is array of atomic_long_t, an attempt
to reduce frequency of updating values in vm_stat[] is achieved by
using per cpu variables "struct per_cpu_pageset"->vm_stat_diff[].
Values in vm_stat_diff[] are merged into vm_stat[] periodically
(configured via /proc/sys/vm/stat_interval) using vmstat_update
workqueue (struct delayed_work vmstat_work).
When a task attempted to allocate memory and reached direct reclaim
path, shrink_zones() checks whether there are reclaimable pages by
calling zone_reclaimable(). zone_reclaimable() makes decision based
on values in vm_stat[] by calling zone_page_state(). This is usually
fine because values in vm_stat_diff[] are expected to be merged into
vm_stat[] shortly.
However, if a workqueue which is processed before vmstat_update
workqueue is processed got stuck inside memory allocation request,
values in vm_stat_diff[] cannot be merged into vm_stat[]. As a result,
zone_reclaimable() continues using outdated vm_stat[] values and the
task which is doing direct reclaim path thinks that there are reclaimable
pages and therefore continues looping. The consequence is a silent
livelock (hang up without any kernel messages) because the OOM killer
will not be invoked.
We can hit such livelock by e.g. disk_events_workfn workqueue doing
memory allocation from bio_copy_kern().
[ 255.054205] kworker/3:1 R running task 0 45 2 0x00000008
[ 255.056063] Workqueue: events_freezable_power_ disk_events_workfn
[ 255.057715] ffff88007f805680 ffff88007c55f6d0 ffffffff8116463d ffff88007c55f758
[ 255.059705] ffff88007f82b870 ffff88007c55f6e0 ffffffff811646be ffff88007c55f710
[ 255.061694] ffffffff811bdaf0 ffff88007f82b870 0000000000000400 0000000000000000
[ 255.063690] Call Trace:
[ 255.064664] [<ffffffff8116463d>] ? __list_lru_count_one.isra.4+0x1d/0x80
[ 255.066428] [<ffffffff811646be>] ? list_lru_count_one+0x1e/0x20
[ 255.068063] [<ffffffff811bdaf0>] ? super_cache_count+0x50/0xd0
[ 255.069666] [<ffffffff8114ecf6>] ? shrink_slab.part.38+0xf6/0x2a0
[ 255.071313] [<ffffffff81151f78>] ? shrink_zone+0x2c8/0x2e0
[ 255.072845] [<ffffffff81152316>] ? do_try_to_free_pages+0x156/0x6d0
[ 255.074527] [<ffffffff810bc6b6>] ? mark_held_locks+0x66/0x90
[ 255.076085] [<ffffffff816ca797>] ? _raw_spin_unlock_irq+0x27/0x40
[ 255.077727] [<ffffffff810bc7d9>] ? trace_hardirqs_on_caller+0xf9/0x1c0
[ 255.079451] [<ffffffff81152924>] ? try_to_free_pages+0x94/0xc0
[ 255.081045] [<ffffffff81145b4a>] ? __alloc_pages_nodemask+0x72a/0xdb0
[ 255.082761] [<ffffffff8118cd06>] ? alloc_pages_current+0x96/0x1b0
[ 255.084407] [<ffffffff8133985d>] ? bio_alloc_bioset+0x20d/0x2d0
[ 255.086032] [<ffffffff8133aba4>] ? bio_copy_kern+0xc4/0x180
[ 255.087584] [<ffffffff81344f20>] ? blk_rq_map_kern+0x70/0x130
[ 255.089161] [<ffffffff814a334d>] ? scsi_execute+0x12d/0x160
[ 255.090696] [<ffffffff814a3474>] ? scsi_execute_req_flags+0x84/0xf0
[ 255.092466] [<ffffffff814b55f2>] ? sr_check_events+0xb2/0x2a0
[ 255.094042] [<ffffffff814c3223>] ? cdrom_check_events+0x13/0x30
[ 255.095634] [<ffffffff814b5a35>] ? sr_block_check_events+0x25/0x30
[ 255.097278] [<ffffffff813501fb>] ? disk_check_events+0x5b/0x150
[ 255.098865] [<ffffffff81350307>] ? disk_events_workfn+0x17/0x20
[ 255.100451] [<ffffffff810890b5>] ? process_one_work+0x1a5/0x420
[ 255.102046] [<ffffffff81089051>] ? process_one_work+0x141/0x420
[ 255.103625] [<ffffffff8108944b>] ? worker_thread+0x11b/0x490
[ 255.105159] [<ffffffff816c4e95>] ? __schedule+0x315/0xac0
[ 255.106643] [<ffffffff81089330>] ? process_one_work+0x420/0x420
[ 255.108217] [<ffffffff8108f4e9>] ? kthread+0xf9/0x110
[ 255.109634] [<ffffffff8108f3f0>] ? kthread_create_on_node+0x230/0x230
[ 255.111307] [<ffffffff816cb35f>] ? ret_from_fork+0x3f/0x70
[ 255.112785] [<ffffffff8108f3f0>] ? kthread_create_on_node+0x230/0x230
[ 273.930846] Showing busy workqueues and worker pools:
[ 273.932299] workqueue events: flags=0x0
[ 273.933465] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=4/256
[ 273.935120] pending: vmpressure_work_fn, vmstat_shepherd, vmstat_update, vmw_fb_dirty_flush [vmwgfx]
[ 273.937489] workqueue events_freezable: flags=0x4
[ 273.938795] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=1/256
[ 273.940446] pending: vmballoon_work [vmw_balloon]
[ 273.941973] workqueue events_power_efficient: flags=0x80
[ 273.943491] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=1/256
[ 273.945167] pending: check_lifetime
[ 273.946422] workqueue events_freezable_power_: flags=0x84
[ 273.947890] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=1/256
[ 273.949579] in-flight: 45:disk_events_workfn
[ 273.951103] workqueue ipv6_addrconf: flags=0x8
[ 273.952447] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=1/1
[ 273.954121] pending: addrconf_verify_work
[ 273.955541] workqueue xfs-reclaim/sda1: flags=0x4
[ 273.957036] pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=1/256
[ 273.958847] pending: xfs_reclaim_worker
[ 273.960392] pool 6: cpus=3 node=0 flags=0x0 nice=0 workers=3 idle: 186 26
This patch changes zone_reclaimable() to use zone_page_state_snapshot()
in order to make sure that values in vm_stat_diff[] are taken into
account when making decision.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index af4f4c0..2e4ef60 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -196,19 +196,19 @@ static unsigned long zone_reclaimable_pages(struct zone *zone)
{
unsigned long nr;
- nr = zone_page_state(zone, NR_ACTIVE_FILE) +
- zone_page_state(zone, NR_INACTIVE_FILE);
+ nr = zone_page_state_snapshot(zone, NR_ACTIVE_FILE) +
+ zone_page_state_snapshot(zone, NR_INACTIVE_FILE);
if (get_nr_swap_pages() > 0)
- nr += zone_page_state(zone, NR_ACTIVE_ANON) +
- zone_page_state(zone, NR_INACTIVE_ANON);
+ nr += zone_page_state_snapshot(zone, NR_ACTIVE_ANON) +
+ zone_page_state_snapshot(zone, NR_INACTIVE_ANON);
return nr;
}
bool zone_reclaimable(struct zone *zone)
{
- return zone_page_state(zone, NR_PAGES_SCANNED) <
+ return zone_page_state_snapshot(zone, NR_PAGES_SCANNED) <
zone_reclaimable_pages(zone) * 6;
}
--
1.8.3.1
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