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Date: Fri, 1 Jun 2012 10:37:30 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Fengguang Wu <fengguang.wu@...el.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujtisu.com>,
Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
Rik van Riel <riel@...hat.com>,
Ying Han <yinghan@...gle.com>,
Greg Thelen <gthelen@...gle.com>,
Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC -mm] memcg: prevent from OOM with too many dirty pages
On Thu 31-05-12 11:09:57, Michal Hocko wrote:
> On Tue 29-05-12 15:51:01, Michal Hocko wrote:
> [...]
> > OK, I have tried it with a simpler approach:
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index c978ce4..e45cf2a 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1294,8 +1294,12 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> > * isolated page is PageWriteback
> > */
> > if (nr_writeback && nr_writeback >=
> > - (nr_taken >> (DEF_PRIORITY - sc->priority)))
> > - wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
> > + (nr_taken >> (DEF_PRIORITY - sc->priority))) {
> > + if (global_reclaim(sc))
> > + wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
> > + else
> > + congestion_wait(BLK_RW_ASYNC, HZ/10);
> > + }
> >
> > trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
> > zone_idx(zone),
> >
> [...]
> > As a conclusion congestion wait performs better (even though I haven't
> > done repeated testing to see what is the deviation) when the
> > reader/writer size doesn't fit into the memcg, while it performs much
> > worse (at least for writer) if it does fit.
> >
> > I will play with that some more
>
> I have, yet again, updated the test. I am writing data to an USB stick
> (with ext3, mounted in sync mode) and which writes 1G in 274.518s,
> 3.8MB/s so the storage is really slow. The parallel read is performed
> from tmpfs and from a local ext3 partition (testing script is attached).
> We start with writing so the LRUs will have some dirty pages when the
> read starts and fill up the LRU with clean page cache.
>
> congestion wait:
> ================
> * ext3 (reader) avg std/avg
> ** Write
> 5M 412.128 334.944 337.708 339.457 356.0593 [10.51%]
> 60M 566.652 321.607 492.025 317.942 424.5565 [29.39%]
> 300M 318.437 315.321 319.515 314.981 317.0635 [0.71%]
> 2G 317.777 314.8 318.657 319.409 317.6608 [0.64%]
>
> ** Read
> 5M 40.1829 40.8907 48.8362 40.0535 42.4908 [9.99%]
> 60M 15.4104 16.1693 18.9162 16.0049 16.6252 [9.39%]
> 300M 17.0376 15.6721 15.6137 15.756 16.0199 [4.25%]
> 2G 15.3718 17.3714 15.3873 15.4554 15.8965 [6.19%]
>
> * Tmpfs (reader)
> ** Write
> 5M 324.425 327.395 573.688 314.884 385.0980 [32.68%]
> 60M 464.578 317.084 375.191 318.947 368.9500 [18.76%]
> 300M 316.885 323.759 317.212 318.149 319.0013 [1.01%]
> 2G 317.276 318.148 318.97 316.897 317.8228 [0.29%]
>
> ** Read
> 5M 0.9241 0.8620 0.9391 1.2922 1.0044 [19.39%]
> 60M 0.8753 0.8359 1.0072 1.3317 1.0125 [22.23%]
> 300M 0.9825 0.8143 0.9864 0.8692 0.9131 [9.35%]
> 2G 0.9990 0.8281 1.0312 0.9034 0.9404 [9.83%]
>
>
> PageReclaim:
> =============
> * ext3 (reader)
> ** Write avg std/avg comparision
> (cong is 100%)
> 5M 313.08 319.924 325.206 325.149 320.8398 [1.79%] 90.11%
> 60M 314.135 415.245 502.157 313.776 386.3283 [23.50%] 91.00%
> 300M 313.718 320.448 315.663 316.714 316.6358 [0.89%] 99.87%
> 2G 317.591 316.67 316.285 316.624 316.7925 [0.18%] 99.73%
>
> ** Read
> 5M 19.0228 20.6743 17.2508 17.5946 18.6356 [8.37%] 43.86%
> 60M 17.3657 15.6402 16.5168 15.5601 16.2707 [5.22%] 97.87%
> 300M 17.1986 15.7616 19.5163 16.9544 17.3577 [9.05%] 108.35%
> 2G 15.6696 15.5384 15.4381 15.2454 15.4729 [1.16%] 97.34%
>
> * Tmpfs (reader)
> ** Write
> 5M 317.303 314.366 316.508 318.883 316.7650 [0.59%] 82.26%
> 60M 579.952 666.606 660.021 655.346 640.4813 [6.34%] 173.60%
> 300M 318.494 318.64 319.516 316.79 318.3600 [0.36%] 99.80%
> 2G 315.935 318.069 321.097 320.329 318.8575 [0.73%] 100.33%
>
> ** Read
> 5M 0.8415 0.8550 0.7892 0.8515 0.8343 [3.67%] 83.07%
> 60M 0.8536 0.8685 0.8237 0.8805 0.8565 [2.86%] 84.60%
> 300M 0.8309 0.8724 0.8553 0.8577 0.8541 [2.01%] 93.53%
> 2G 0.8427 0.8468 0.8325 1.4658 0.9970 [31.36%] 106.01%
And just finished a test without any patch (current memcg-devel tree).
Surprisingly enough OOM killer didn't trigger in this setup (the storage
is probably too slow):
avg std/avg comparison comparison
(cong is 100%) (page reclaim 100%)
ext3 (reader)
** Write
5M 329.953 319.305 705.561 338.379 423.2995 [44.49%] 118.88% 131.93%
60M 320.940 529.418 314.126 552.817 429.3253 [30.16%] 101.12% 111.13%
300M 315.600 318.759 314.052 313.366 315.4443 [0.76%] 99.49% 99.62%
2G 316.799 313.328 316.605 317.873 316.151 [0.62%] 99.52% 99.80%
** Read
5M 17.2729 15.9298 15.5007 15.7594 16.1157 [4.91%] 37.93% 86.48%
60M 16.0478 15.8576 16.7704 16.9675 16.4108 [3.29%] 98.71% 100.86%
300M 15.7392 15.5122 15.5084 15.6455 15.6013 [0.72%] 97.39% 89.88%
2G 15.3784 15.3592 15.5804 15.6464 15.4911 [0.93%] 97.45% 100.12%
Tmpfs (reader)
** write
5M 313.910 504.897 699.040 352.671 467.6295 [37.40%] 121.43% 147.63%
60M 654.229 316.980 316.147 651.824 484.7950 [40.07%] 131.40% 75.69%
300M 315.442 317.248 316.668 316.163 316.3803 [0.24%] 99.18% 99.38%
2G 316.971 315.687 316.283 316.879 316.4550 [0.19%] 99.57% 99.25%
** read
5M 0.8013 1.1041 0.8345 0.8223 0.8906 [16.06%] 88.67% 106.74%
60M 0.8312 0.7887 0.8577 0.8273 0.8262 [3.44%] 81.60% 96.46%
300M 1.1530 0.8674 1.1260 1.1116 1.0645 [12.45%] 116.58% 124.64%
2G 0.8318 0.8323 0.8897 0.8278 0.8454 [3.50%] 89.89% 84.79%
Write performance is within the noise. Sometimes the patched kernel does
much better, especially for the small groups.
Read performance is more interesting. We seem to regress. The PageReclaim
approach seem to regrees less than congestion_wait.
The biggest drop down seems to be for cong. wait and reader from ext3
with 5M cgroup (there was no big peak during that run ~10% std/avg and
the performance is steady also without any patches).
More detailed statistics (max/min - the worst/best performance).
comparison (cong is 100%) comparison (page reclaim 100%)
max min median max min median
* ext3
** Write
5M 171.20% 95.33% 98.70% 216.96% 101.99% 103.61%
60M 97.56% 98.80% 104.51% 110.09% 100.11% 116.59%
300M 99.76% 99.49% 99.35% 99.47% 99.89% 99.57%
2G 99.52% 99.53% 99.52% 100.09% 99.07% 100.02%
** Read
5M 35.37% 38.70% 39.09% 83.55% 89.85% 86.54%
60M 89.70% 102.90% 102.00% 97.71% 101.91% 102.06%
300M 92.38% 99.33% 99.14% 80.65% 98.39% 91.23%
2G 90.07% 99.92% 100.38% 99.85% 100.75% 99.94%
* Tmpfs
** write
5M 121.85% 99.69% 131.57% 219.22% 99.85% 135.30%
60M 140.82% 99.70% 139.57% 98.14% 54.51% 73.65%
300M 97.99% 99.54% 99.60% 99.29% 99.57% 99.32%
2G 99.37% 99.62% 99.64% 98.72% 99.92% 99.18%
** read
5M 85.44% 92.96% 88.92% 129.13% 101.54% 97.87%
60M 64.41% 94.35% 88.10% 97.41% 95.75% 96.31%
300M 116.89% 106.52% 120.84% 132.17% 104.39% 130.63%
2G 86.27% 99.96% 87.47% 60.69% 99.44% 98.49%
These numbers show that PageReclaim gives us slightly better results
than congestion wait. There are not so big dropdowns (like 5M ext3 read
or 60M tmpfs read).
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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