(2012/03/23 18:15), bill4carson wrote: > > > On 2012年03月23日 17:04, KAMEZAWA Hiroyuki wrote: >> (2012/03/23 17:59), bill4carson wrote: >> >>> >>> >>> On 2012年03月23日 16:19, KAMEZAWA Hiroyuki wrote: >>>> (2012/03/23 17:04), bill4carson wrote: >>>> >>>>> Hi, all >>>>> >>>>> I'm playing with memory cgroup, I'm a bit confused why >>>>> memory.usage in bytes is steadily increasing at 4K page pace >>>>> after every mmap/dirty/unmap sequence. >>>>> >>>>> On linux-3.6.34.10/linux-3.3.0-rc5 >>>>> A simple test case does following: >>>>> >>>>> a) mmap 128k memory in private anonymous way >>>>> b) dirty all 128k to demand physical page >>>>> c) print memory.usage_in_bytes<-- increased at 4K after every loop >>>>> d) unmap previous 128 memory >>>>> e) goto a) to repeat >>>> >>>> In Documentation/cgroup/memory.txt >>>> == >>>> 5.5 usage_in_bytes >>>> >>>> For efficiency, as other kernel components, memory cgroup uses some optimization >>>> to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the >>>> method and doesn't show 'exact' value of memory(and swap) usage, it's an fuzz >>>> value for efficient access. (Of course, when necessary, it's synchronized.) >>>> If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP) >>>> value in memory.stat(see 5.2). >>>> == >>>> >>>> In current implementation, memcg tries to charge resource in size of 32 pages. >>>> So, if you get 32 pages and free 32pages, usage_in_bytes may not change. >>>> This is affected by caches in other cpus and other flushing operations caused >>>> by some workload in other cgroups. memcg's usage_in_bytes is not precise in >>>> 128k degree. >>>> >>> Yes, I tried to mmap/dirty/unmap in 32 times, when the usage_in_bytes >>> reached 128k, it rolls back to 4k again. So it doesn't hurt any more. >> >> >> rolls back before unmap() ? >> > After unmap > >>> >>> I haven't found the code regarding to this behavior. >> >> >> Could you post your test program ? >> > Yes, it's a bit of messy, you can mock at me:) Thank you. I tried. I checked /proc/<pid>/smaps and compares it before I press 'm' and after I press 'm'. So, anonymous should be increased 128k. Then... == [root@bluextal kamezawa]# diff -Nru before.txt after.txt | grep Anonymous Anonymous: 0 kB -Anonymous: 12 kB +Anonymous: 140 kB <============= 128kbytes you allocated -Anonymous: 8 kB +Anonymous: 12 kB <============= maybe some library's heap. == Then, 4k remains even if you free all allocated area by your program, I think. Thanks, -Kame -- 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>