On Fri, May 27, 2011 at 1:33 AM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > On Thu, 26 May 2011 21:45:28 -0700 > Ying Han <yinghan@xxxxxxxxxx> wrote: > >> On Thu, May 26, 2011 at 7:11 PM, KAMEZAWA Hiroyuki >> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >> > On Thu, 26 May 2011 18:40:44 -0700 >> > Ying Han <yinghan@xxxxxxxxxx> wrote: >> > >> >> On Thu, May 26, 2011 at 5:31 PM, KAMEZAWA Hiroyuki >> >> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >> >> > On Thu, 26 May 2011 17:23:20 -0700 >> >> > Ying Han <yinghan@xxxxxxxxxx> wrote: >> >> > >> >> >> On Thu, May 26, 2011 at 5:05 PM, KAMEZAWA Hiroyuki < >> >> >> kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >> >> >> >> >> >> > On Thu, 26 May 2011 14:07:49 -0700 >> >> >> > Ying Han <yinghan@xxxxxxxxxx> wrote: >> >> >> > >> >> >> > > This adds histogram to capture pagefault latencies on per-memcg basis. I >> >> >> > used >> >> >> > > this patch on the memcg background reclaim test, and figured there could >> >> >> > be more >> >> >> > > usecases to monitor/debug application performance. >> >> >> > > >> >> >> > > The histogram is composed 8 bucket in ns unit. The last one is infinite >> >> >> > (inf) >> >> >> > > which is everything beyond the last one. To be more flexible, the buckets >> >> >> > can >> >> >> > > be reset and also each bucket is configurable at runtime. >> >> >> > > >> >> >> > > memory.pgfault_histogram: exports the histogram on per-memcg basis and >> >> >> > also can >> >> >> > > be reset by echoing "reset". Meantime, all the buckets are writable by >> >> >> > echoing >> >> >> > > the range into the API. see the example below. >> >> >> > > >> >> >> > > /proc/sys/vm/pgfault_histogram: the global sysfs tunablecan be used to >> >> >> > turn >> >> >> > > on/off recording the histogram. >> >> >> > > >> >> >> > > Functional Test: >> >> >> > > Create a memcg with 10g hard_limit, running dd & allocate 8g anon page. >> >> >> > > Measure the anon page allocation latency. >> >> >> > > >> >> >> > > $ mkdir /dev/cgroup/memory/B >> >> >> > > $ echo 10g >/dev/cgroup/memory/B/memory.limit_in_bytes >> >> >> > > $ echo $$ >/dev/cgroup/memory/B/tasks >> >> >> > > $ dd if=/dev/zero of=/export/hdc3/dd/tf0 bs=1024 count=20971520 & >> >> >> > > $ allocate 8g anon pages >> >> >> > > >> >> >> > > $ echo 1 >/proc/sys/vm/pgfault_histogram >> >> >> > > >> >> >> > > $ cat /dev/cgroup/memory/B/memory.pgfault_histogram >> >> >> > > pgfault latency histogram (ns): >> >> >> > > < 600 2051273 >> >> >> > > < 1200 40859 >> >> >> > > < 2400 4004 >> >> >> > > < 4800 1605 >> >> >> > > < 9600 170 >> >> >> > > < 19200 82 >> >> >> > > < 38400 6 >> >> >> > > < inf 0 >> >> >> > > >> >> >> > > $ echo reset >/dev/cgroup/memory/B/memory.pgfault_histogram >> >> >> > > $ cat /dev/cgroup/memory/B/memory.pgfault_histogram >> >> >> > > pgfault latency histogram (ns): >> >> >> > > < 600 0 >> >> >> > > < 1200 0 >> >> >> > > < 2400 0 >> >> >> > > < 4800 0 >> >> >> > > < 9600 0 >> >> >> > > < 19200 0 >> >> >> > > < 38400 0 >> >> >> > > < inf 0 >> >> >> > > >> >> >> > > $ echo 500 520 540 580 600 1000 5000 >> >> >> > >/dev/cgroup/memory/B/memory.pgfault_histogram >> >> >> > > $ cat /dev/cgroup/memory/B/memory.pgfault_histogram >> >> >> > > pgfault latency histogram (ns): >> >> >> > > < 500 50 >> >> >> > > < 520 151 >> >> >> > > < 540 3715 >> >> >> > > < 580 1859812 >> >> >> > > < 600 202241 >> >> >> > > < 1000 25394 >> >> >> > > < 5000 5875 >> >> >> > > < inf 186 >> >> >> > > >> >> >> > > Performance Test: >> >> >> > > I ran through the PageFaultTest (pft) benchmark to measure the overhead >> >> >> > of >> >> >> > > recording the histogram. There is no overhead observed on both >> >> >> > "flt/cpu/s" >> >> >> > > and "fault/wsec". >> >> >> > > >> >> >> > > $ mkdir /dev/cgroup/memory/A >> >> >> > > $ echo 16g >/dev/cgroup/memory/A/memory.limit_in_bytes >> >> >> > > $ echo $$ >/dev/cgroup/memory/A/tasks >> >> >> > > $ ./pft -m 15g -t 8 -T a >> >> >> > > >> >> >> > > Result: >> >> >> > > "fault/wsec" >> >> >> > > >> >> >> > > $ ./ministat no_histogram histogram >> >> >> > > x no_histogram >> >> >> > > + histogram >> >> >> > > >> >> >> > +--------------------------------------------------------------------------+ >> >> >> > > N Min Max Median Avg >> >> >> > Stddev >> >> >> > > x 5 813404.51 824574.98 821661.3 820470.83 >> >> >> > 4202.0758 >> >> >> > > + 5 821228.91 825894.66 822874.65 823374.15 >> >> >> > 1787.9355 >> >> >> > > >> >> >> > > "flt/cpu/s" >> >> >> > > >> >> >> > > $ ./ministat no_histogram histogram >> >> >> > > x no_histogram >> >> >> > > + histogram >> >> >> > > >> >> >> > +--------------------------------------------------------------------------+ >> >> >> > > N Min Max Median Avg >> >> >> > Stddev >> >> >> > > x 5 104951.93 106173.13 105142.73 105349.2 >> >> >> > 513.78158 >> >> >> > > + 5 104697.67 105416.1 104943.52 104973.77 >> >> >> > 269.24781 >> >> >> > > No difference proven at 95.0% confidence >> >> >> > > >> >> >> > > Signed-off-by: Ying Han <yinghan@xxxxxxxxxx> >> >> >> > >> >> >> > Hmm, interesting....but isn't it very very very complicated interface ? >> >> >> > Could you make this for 'perf' ? Then, everyone (including someone who >> >> >> > don't use memcg) >> >> >> > will be happy. >> >> >> > >> >> >> >> >> >> Thank you for looking at it. >> >> >> >> >> >> There is only one per-memcg API added which is basically exporting the >> >> >> histogram. The "reset" and reconfiguring the bucket is not "must" but make >> >> >> it more flexible. Also, the sysfs API can be reduced if necessary since >> >> >> there is no over-head observed by always turning it on anyway. >> >> >> >> >> >> I am not familiar w/ perf, any suggestions how it is supposed to be look >> >> >> like? >> >> >> >> >> >> Thanks >> >> >> >> >> > >> >> > IIUC, you can record "all" latency information by perf record. Then, latency >> >> > information can be dumped out to some file. >> >> > >> >> > You can add a python? script for perf as >> >> > >> >> > # perf report memory-reclaim-latency-histgram -f perf.data >> >> > -o 500,1000,1500,2000..... >> >> > ...show histgram in text.. or report the histgram in graphic. >> >> > >> >> > Good point is >> >> > - you can reuse perf.data and show histgram from another point of view. >> >> > >> >> > - you can show another cut of view, for example, I think you can write a >> >> > parser to show "changes in hisgram by time", easily. >> >> > You may able to generate a movie ;) >> >> > >> >> > - Now, perf cgroup is supported. Then, >> >> > - you can see per task histgram >> >> > - you can see per cgroup histgram >> >> > - you can see per system-wide histgram >> >> > (If you record latency of usual kswapd/alloc_pages) >> >> > >> >> > - If you record latency within shrink_zone(), you can show per-zone >> >> > reclaim latency histgram. record parsers can gather them and >> >> > show histgram. This will be benefical to cpuset users. >> >> > >> >> > >> >> > I'm sorry if I miss something. >> >> >> >> After study a bit on perf, it is not feasible in this casecase. The >> >> cpu & memory overhead of perf is overwhelming.... Each page fault will >> >> generate a record in the buffer and how many data we can record in the >> >> buffer, and how many data will be processed later.. Most of the data >> >> that is recorded by the general perf framework is not needed here. >> >> >> > >> > I disagree. "each page fault" is not correct. "every lru scan" is correct. >> > Then, record to buffer will be at most memory.failcnt times. >> >> Hmm. Sorry I might miss something here... :( >> >> The page fault histogram recorded is per page-fault, only the ones >> trigger reclaim. The background reclaim testing is just one usecase of >> it, and we need this information for more >> general usage to monitor application performance. So i recorded the >> latency for each single page fault. >> > > BTW, why page-fault only ? For some applications, file cache is more imporatant. > I think usual page fault's usual cost is not in interest. > you can get PGPGIN statistics from other source. > > Anyway, I think it's better for record reclaim latency. Sounds reasonable. I will add that in the next post. Thanks for reviewing --Ying > > > Thanks, > -Kame > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . 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