Re: [RFC][PATCH v3 0/10] memcg async reclaim

[Ying Han <yinghan@google.com>]

On Thu, May 26, 2011 at 9:34 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Thu, 26 May 2011 21:33:32 -0700
> Ying Han <yinghan@google.com> wrote:
>
>> On Thu, May 26, 2011 at 7:16 PM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> > On Thu, 26 May 2011 18:49:26 -0700
>> > Ying Han <yinghan@google.com> wrote:
>> >
>> >> On Wed, May 25, 2011 at 10:10 PM, KAMEZAWA Hiroyuki
>> >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> >> >
>> >> > It's now merge window...I just dump my patch queue to hear other's idea.
>> >> > I wonder I should wait until dirty_ratio for memcg is queued to mmotm...
>> >> > I'll be busy with LinuxCon Japan etc...in the next week.
>> >> >
>> >> > This patch is onto mmotm-May-11 + some patches queued in mmotm, as numa_stat.
>> >> >
>> >> > This is a patch for memcg to keep margin to the limit in background.
>> >> > By keeping some margin to the limit in background, application can
>> >> > avoid foreground memory reclaim at charge() and this will help latency.
>> >> >
>> >> > Main changes from v2 is.
>> >> >  - use SCHED_IDLE.
>> >> >  - removed most of heuristic codes. Now, code is very simple.
>> >> >
>> >> > By using SCHED_IDLE, async memory reclaim can only consume 0.3%? of cpu
>> >> > if the system is truely busy but can use much CPU if the cpu is idle.
>> >> > Because my purpose is for reducing latency without affecting other running
>> >> > applications, SCHED_IDLE fits this work.
>> >> >
>> >> > If application need to stop by some I/O or event, background memory reclaim
>> >> > will cull memory while the system is idle.
>> >> >
>> >> > Perforemce:
>> >> >  Running an httpd (apache) under 300M limit. And access 600MB working set
>> >> >  with normalized distribution access by apatch-bench.
>> >> >  apatch bench's concurrency was 4 and did 40960 accesses.
>> >> >
>> >> > Without async reclaim:
>> >> > Connection Times (ms)
>> >> >              min  mean[+/-sd] median   max
>> >> > Connect:        0    0   0.0      0       2
>> >> > Processing:    30   37  28.3     32    1793
>> >> > Waiting:       28   35  25.5     31    1792
>> >> > Total:         30   37  28.4     32    1793
>> >> >
>> >> > Percentage of the requests served within a certain time (ms)
>> >> >  50%     32
>> >> >  66%     32
>> >> >  75%     33
>> >> >  80%     34
>> >> >  90%     39
>> >> >  95%     60
>> >> >  98%    100
>> >> >  99%    133
>> >> >  100%   1793 (longest request)
>> >> >
>> >> > With async reclaim:
>> >> > Connection Times (ms)
>> >> >              min  mean[+/-sd] median   max
>> >> > Connect:        0    0   0.0      0       2
>> >> > Processing:    30   35  12.3     32     678
>> >> > Waiting:       28   34  12.0     31     658
>> >> > Total:         30   35  12.3     32     678
>> >> >
>> >> > Percentage of the requests served within a certain time (ms)
>> >> >  50%     32
>> >> >  66%     32
>> >> >  75%     33
>> >> >  80%     34
>> >> >  90%     39
>> >> >  95%     49
>> >> >  98%     71
>> >> >  99%     86
>> >> >  100%    678 (longest request)
>> >> >
>> >> >
>> >> > It seems latency is stabilized by hiding memory reclaim.
>> >> >
>> >> > The score for memory reclaim was following.
>> >> > See patch 10 for meaning of each member.
>> >> >
>> >> > == without async reclaim ==
>> >> > recent_scan_success_ratio 44
>> >> > limit_scan_pages 388463
>> >> > limit_freed_pages 162238
>> >> > limit_elapsed_ns 13852159231
>> >> > soft_scan_pages 0
>> >> > soft_freed_pages 0
>> >> > soft_elapsed_ns 0
>> >> > margin_scan_pages 0
>> >> > margin_freed_pages 0
>> >> > margin_elapsed_ns 0
>> >> >
>> >> > == with async reclaim ==
>> >> > recent_scan_success_ratio 6
>> >> > limit_scan_pages 0
>> >> > limit_freed_pages 0
>> >> > limit_elapsed_ns 0
>> >> > soft_scan_pages 0
>> >> > soft_freed_pages 0
>> >> > soft_elapsed_ns 0
>> >> > margin_scan_pages 1295556
>> >> > margin_freed_pages 122450
>> >> > margin_elapsed_ns 644881521
>> >> >
>> >> >
>> >> > For this case, SCHED_IDLE workqueue can reclaim enough memory to the httpd.
>> >> >
>> >> > I may need to dig why scan_success_ratio is far different in the both case.
>> >> > I guess the difference of epalsed_ns is because several threads enter
>> >> > memory reclaim when async reclaim doesn't run. But may not...
>> >> >
>> >>
>> >>
>> >> Hmm.. I noticed a very strange behavior on a simple test w/ the patch set.
>> >>
>> >> Test:
>> >> I created a 4g memcg and start doing cat. Then the memcg being OOM
>> >> killed as soon as it reaches its hard_limit. We shouldn't hit OOM even
>> >> w/o async-reclaim.
>> >>
>> >> Again, I will read through the patch. But like to post the test result first.
>> >>
>> >> $ echo $$ >/dev/cgroup/memory/A/tasks
>> >> $ cat /dev/cgroup/memory/A/memory.limit_in_bytes
>> >> 4294967296
>> >>
>> >> $ time cat /export/hdc3/dd_A/tf0 > /dev/zero
>> >> Killed
>> >>
>> >
>> > I did the same kind of test without any problem...but ok, I'll do more test
>> > later.
>> >
>> >
>> >
>> >> real  0m53.565s
>> >> user  0m0.061s
>> >> sys   0m4.814s
>> >>
>> >> Here is the OOM log:
>> >>
>> >> May 26 18:43:00  kernel: [  963.489112] cat invoked oom-killer:
>> >> gfp_mask=0xd0, order=0, oom_adj=0, oom_score_adj=0
>> >> May 26 18:43:00  kernel: [  963.489121] Pid: 9425, comm: cat Tainted:
>> >> G        W   2.6.39-mcg-DEV #131
>> >> May 26 18:43:00  kernel: [  963.489123] Call Trace:
>> >> May 26 18:43:00  kernel: [  963.489134]  [<ffffffff810e3512>]
>> >> dump_header+0x82/0x1af
>> >> May 26 18:43:00  kernel: [  963.489137]  [<ffffffff810e33ca>] ?
>> >> spin_lock+0xe/0x10
>> >> May 26 18:43:00  kernel: [  963.489140]  [<ffffffff810e33f9>] ?
>> >> find_lock_task_mm+0x2d/0x67
>> >> May 26 18:43:00  kernel: [  963.489143]  [<ffffffff810e38dd>]
>> >> oom_kill_process+0x50/0x27b
>> >> May 26 18:43:00  kernel: [  963.489155]  [<ffffffff810e3dc6>]
>> >> mem_cgroup_out_of_memory+0x9a/0xe4
>> >> May 26 18:43:00  kernel: [  963.489160]  [<ffffffff811153aa>]
>> >> mem_cgroup_handle_oom+0x134/0x1fe
>> >> May 26 18:43:00  kernel: [  963.489163]  [<ffffffff81114a72>] ?
>> >> __mem_cgroup_insert_exceeded+0x83/0x83
>> >> May 26 18:43:00  kernel: [  963.489176]  [<ffffffff811166e9>]
>> >> __mem_cgroup_try_charge.clone.3+0x368/0x43a
>> >> May 26 18:43:00  kernel: [  963.489179]  [<ffffffff81117586>]
>> >> mem_cgroup_cache_charge+0x95/0x123
>> >> May 26 18:43:00  kernel: [  963.489183]  [<ffffffff810e16d8>]
>> >> add_to_page_cache_locked+0x42/0x114
>> >> May 26 18:43:00  kernel: [  963.489185]  [<ffffffff810e17db>]
>> >> add_to_page_cache_lru+0x31/0x5f
>> >> May 26 18:43:00  kernel: [  963.489189]  [<ffffffff81145636>]
>> >> mpage_readpages+0xb6/0x132
>> >> May 26 18:43:00  kernel: [  963.489194]  [<ffffffff8119992f>] ?
>> >> noalloc_get_block_write+0x24/0x24
>> >> May 26 18:43:00  kernel: [  963.489197]  [<ffffffff8119992f>] ?
>> >> noalloc_get_block_write+0x24/0x24
>> >> May 26 18:43:00  kernel: [  963.489201]  [<ffffffff81036742>] ?
>> >> __switch_to+0x160/0x212
>> >> May 26 18:43:00  kernel: [  963.489205]  [<ffffffff811978b2>]
>> >> ext4_readpages+0x1d/0x1f
>> >> May 26 18:43:00  kernel: [  963.489209]  [<ffffffff810e8d4b>]
>> >> __do_page_cache_readahead+0x144/0x1e3
>> >> May 26 18:43:00  kernel: [  963.489212]  [<ffffffff810e8e0b>]
>> >> ra_submit+0x21/0x25
>> >> May 26 18:43:00  kernel: [  963.489215]  [<ffffffff810e9075>]
>> >> ondemand_readahead+0x18c/0x19f
>> >> May 26 18:43:00  kernel: [  963.489218]  [<ffffffff810e9105>]
>> >> page_cache_async_readahead+0x7d/0x86
>> >> May 26 18:43:00  kernel: [  963.489221]  [<ffffffff810e2b7e>]
>> >> generic_file_aio_read+0x2d8/0x5fe
>> >> May 26 18:43:00  kernel: [  963.489225]  [<ffffffff81119626>]
>> >> do_sync_read+0xcb/0x108
>> >> May 26 18:43:00  kernel: [  963.489230]  [<ffffffff811f168a>] ?
>> >> fsnotify_perm+0x66/0x72
>> >> May 26 18:43:00  kernel: [  963.489233]  [<ffffffff811f16f7>] ?
>> >> security_file_permission+0x2e/0x33
>> >> May 26 18:43:00  kernel: [  963.489236]  [<ffffffff8111a0c8>]
>> >> vfs_read+0xab/0x107
>> >> May 26 18:43:00  kernel: [  963.489239]  [<ffffffff8111a1e4>] sys_read+0x4a/0x6e
>> >> May 26 18:43:00  kernel: [  963.489244]  [<ffffffff8140f469>]
>> >> sysenter_dispatch+0x7/0x27
>> >> May 26 18:43:00  kernel: [  963.489248] Task in /A killed as a result
>> >> of limit of /A
>> >> May 26 18:43:00  kernel: [  963.489251] memory: usage 4194304kB, limit
>> >> 4194304kB, failcnt 26
>> >> May 26 18:43:00  kernel: [  963.489253] memory+swap: usage 0kB, limit
>> >> 9007199254740991kB, failcnt 0
>> >>
>> >
>> > Hmm, why memory+swap usage 0kb here...
>> >
>> > In this set, I used mem_cgroup_margin() rather than res_counter_margin().
>> > Hmm, do you disable swap accounting ? If so, I may miss some.
>>
>> Yes, I disabled the swap accounting in .config:
>> # CONFIG_CGROUP_MEM_RES_CTLR_SWAP is not set
>>
>>
>> Here is how i reproduce it:
>>
>> $ mkdir /dev/cgroup/memory/D
>> $ echo 4g >/dev/cgroup/memory/D/memory.limit_in_bytes
>>
>> $ cat /dev/cgroup/memory/D/memory.limit_in_bytes
>> 4294967296
>>
>> $ cat /dev/cgroup/memory/D/memory.
>> memory.async_control             memory.max_usage_in_bytes
>> memory.soft_limit_in_bytes       memory.use_hierarchy
>> memory.failcnt                   memory.move_charge_at_immigrate
>> memory.stat
>> memory.force_empty               memory.oom_control
>> memory.swappiness
>> memory.limit_in_bytes            memory.reclaim_stat
>> memory.usage_in_bytes
>>
>> $ cat /dev/cgroup/memory/D/memory.async_control
>> 0
>> $ echo 1 >/dev/cgroup/memory/D/memory.async_control
>> $ cat /dev/cgroup/memory/D/memory.async_control
>> 1
>>
>> $ echo $$ >/dev/cgroup/memory/D/tasks
>> $ cat /proc/4358/cgroup
>> 3:memory:/D
>>
>> $ time cat /export/hdc3/dd_A/tf0 > /dev/zero
>> Killed
>>
>
> If you applied my patches collectly, async_control can be seen if
> swap controller is configured because of BUG in patch.

I noticed the BUG at the very beginning, so all my tests are having the fix.

>
> I could cat 20G file under 4G limit without any problem with boot option
> swapaccount=0. no problem if async_control == 0 ?

$ cat /dev/cgroup/memory/D/memory.async_control
1

I have the .config
# CONFIG_CGROUP_MEM_RES_CTLR_SWAP is not set

Not sure if that makes difference. I will test next to turn that on.

--Ying


>
>
>
> Thanks,
> -Kame
>
>
>
>

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