https://bugzilla.novell.com/show_bug.cgi?id=879071
https://bugzilla.novell.com/show_bug.cgi?id=879071#c3
Michal Hocko changed:
What |Removed |Added
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CC| |mhocko@suse.com
--- Comment #3 from Michal Hocko 2014-05-22 15:25:42 CEST ---
Here are some counters from vmstat data. First line is an aboslute number and
all the following lines are diff to previous.
time nr_dirtied nr_dirty nr_written allocstall
pgsteal_direct_dma32 pgscan_direct_dma32
pgsteal_kswapd_dma32/pgscan_kswapd_dma32[%]
1400672643.810787699 39520729 10 37833453 18685 1707363
2696767 81.71
1.00703 0 0 0 0 0 0 0.00
1.00493 4 4 0 0 0 0 0.00
1.01195 34697 26244 7000 6 219 256 43.79
1.00892 2936 -5021 10145 5 370 370 45.74
1.01036 13107 -95 10057 8 271 515 40.17
1.00863 14373 4594 9495 3 302 302 64.25
1.00877 6894 -3427 10284 8 193 910 34.88
1.31147 11541 -1310 13539 16 895 914 53.85 <<<
1.00941 14969 3980 9916 10 389 421 55.14
1.0086 4763 -5595 10430 2 176 920 31.37
1.01123 15491 5180 10169 8 512 512 54.18
1.00951 11298 942 10215 9 407 1038 56.67
1.00873 3703 -5740 10168 4 238 276 22.54
1.91098 12459 -6928 19335 10 394 1415 53.45 <<<
1.00859 19852 9406 10229 22 1096 1890 55.47
2.10967 18650 -3028 21341 9 699 1668 49.37 <<<
1.00987 7760 -2037 10243 13 488 775 44.11
1.00988 17009 6786 9863 14 745 1372 63.44
As we can see kswapd doesn't reclaim fast enough so we are permanently in the
direct reclaim. kswapd effectivity (reclaimed/scanned) drops down a lot before
stalls. I assume that kswapd sees a lot of dirty pages which are not pushed to
the storage fast enough. The writeback speed seems to be quite constant ~10k/s
so the IO doesn't seem to be the main problem here. This looks like the writer
is not throttled enough wrt. to the device speed.
So this looks like the old and known problem that dirty_{ratio,bytes} is too
high for the slow device :/
There is a per-bdi max_ratio tunable which might help here. Jack will surely
know more about this.
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