Michal Hocko said the following on 2012-1-4 0:04: > On Wed 28-12-11 17:23:04, Peng Haitao wrote: >> >> memory.memsw.failcnt shows the number of memory+Swap hits limits. >> So I think when memory+swap usage is equal to limit, memsw.failcnt should be nonzero. >> >> I test as follows: >> >> # uname -a >> Linux K-test 3.2.0-rc7-17-g371de6e #2 SMP Wed Dec 28 12:02:52 CST 2011 x86_64 x86_64 x86_64 GNU/Linux >> # mkdir /cgroup/memory/group >> # cd /cgroup/memory/group/ >> # echo 10M > memory.limit_in_bytes >> # echo 10M > memory.memsw.limit_in_bytes >> # echo $$ > tasks >> # dd if=/dev/zero of=/tmp/temp_file count=20 bs=1M >> Killed >> # cat memory.memsw.failcnt >> 0 >> # grep "failcnt" /var/log/messages | tail -2 >> Dec 28 17:05:52 K-test kernel: memory: usage 10240kB, limit 10240kB, failcnt 21 >> Dec 28 17:05:52 K-test kernel: memory+swap: usage 10240kB, limit 10240kB, failcnt 0 >> >> memory+swap usage is equal to limit, but memsw.failcnt is zero. >> > Please note that memsw.limit_in_bytes is triggered only if we have > consumed some swap space already (and the feature is primarily intended > to stop extensive swap usage in fact). > It goes like this: If we trigger hard limit (memory.limit_in_bytes) then > we start the direct reclaim (with swap available). If we trigger memsw > limit then we try to reclaim without swap available. We will OOM if we > cannot reclaim enough to satisfy the respective limit. > > The other part of the answer is, yes there is something wrong going > on her because we definitely shouldn't OOM. The workload is a single > threaded and we have a plenty of page cache that could be reclaimed > easily. On the other hand we end up with: > # echo $$ > tasks > /dev/memctl/a# echo 10M > memory.limit_in_bytes > /dev/memctl/a# echo 10M > memory.memsw.limit_in_bytes > /dev/memctl/a# dd if=/dev/zero of=/tmp/temp_file count=20 bs=1M > Killed > /dev/memctl/a# cat memory.stat > cache 9265152 > [...] > > So there is almost 10M of page cache that we can simply reclaim. If we > use 40M limit then we are OK. So this looks like the small limit somehow > tricks our math in the reclaim path and we think there is nothing to > reclaim. > I will look into this. Have any conclusion for this? Thanks. -- Best Regards, Peng -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>