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

    --Ying


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