Hi Michal
Thanks for your kindly support.
I got a device, and dump the /proc/meminfo and /proc/vmstat files, they are the Linux standard proc files.
I found that: Cached = 339880 KB, but nr_free_pages=14675*4 = 58700KB and nr_shmem = 508*4=2032KB

nr_shmem is just a little memory, and nr free pages + nr_shmem is largely less than Cached.
So why nr_free_pages is largely less than Cached? Thank you.

$ adb shell cat /proc/meminfo
MemTotal:        1366904 kB
MemFree:           59040 kB
Buffers:           54600 kB
Cached:           339880 kB

$ adb shell cat /proc/vmstat
nr_free_pages 14675
nr_inactive_anon 73520
nr_shmem 508

Thanks
Zhiyuan zhu

-----邮件原件-----
发件人: Michal Hocko [mailto:mhocko@suse.cz] 
发送时间: 2014年11月20日 17:58
收件人: Zhiyuan Zhu(朱志遠)
抄送: hannes@cmpxchg.org; Future Zhou(周未來); Rachel Zhang(張瑩); bsingharora@gmail.com; kamezawa.hiroyu@jp.fujitsu.com; cgroups@vger.kernel.org; linux-mm@kvack.org; Greg KH
主题: Re: low memory killer

[Adding Greg to CC as the current maintainer of the staging and dropping majordomo]

I am not Johannes but,

On Thu 20-11-14 09:26:05, zhiyuan_zhu@htc.com wrote:
> hi Johannes
> 
> My name is Zhiyuan zhu, an android development engineer in htc.
> We encounter a lowmemorykiller’s problem.
> Coluld you help to kindly support? Thank you.

Please note that lowmemory killer is not part of Memory cgroup resource controller. It is a staging driver which is supposed to be supported by support by Android people. I am not sure about the current state but the implementation and some concepts used to be broken in many ways.
Anyway I think the driver should be dropped from the tree or try to get promoted to the regular tree _after_ it passes a proper review.
 
> Problem describtion:
> We noticed that gap of dumping cached value from “lowmemorykiller”
> and “/proc/meminfo/” are different apparently. Like example below, 
> lowmemorykiller showed cache only has 72460kB while launcher was 
> killed, but /proc/meminfo showed cached still has 142448kB. Please 
> check why the gap of cache value between lowmemorykill and 
> /proc/meminfo are huge.

lowmem_scan prints:
other_file = global_page_state(NR_FILE_PAGES) - global_page_state(NR_SHMEM) - total_swapcache_pages();

as per meminfo_proc_show(), Cached value corresponds to:
        cached = global_page_state(NR_FILE_PAGES) - total_swapcache_pages() - i.bufferram;

So those two values are quite different. E.g. lowmem killer ignores shmem pages. This can be considerable amount of memory.

> kernel_e0058_0001_20141107_204711_LC4ABYA00200_htc_a31ul_0.54.999.1.txt at LC4ABYA00200
>         6      161030.084144       2014-11-07 21:44:53.304        lowmemorykiller: Killing 'om.htc.launcher' (4486), adj 294,
> 6      161030.084144       2014-11-07 21:44:53.304           to free 47856kB on behalf of 'kworker/u8:14' (20594) because
> 6      161030.084144       2014-11-07 21:44:53.304           cache 72460kB is below limit 73728kB for oom_score_adj 235
> 6      161030.084144       2014-11-07 21:44:53.304           Free memory is 51304kB above reserved
> 4      161030.084797       2014-11-07 21:44:53.304        MemFree:           55676 kB
> 4      161030.084797       2014-11-07 21:44:53.304        Buffers:            1240 kB
> 4      161030.084797       2014-11-07 21:44:53.304        Cached:           142448 kB

I do not see any code in drivers/staging/android/lowmemorykiller.c that would print such an information in the current tree.

> Lowmemorykiller calculated cache value is 72460kB, but the 
> /proc/meminfo’s cached is 142448 kB
> 
> After checked the code, I found that:
> Lowmemorykiller’s memory information is comes from /proc/zoneinfo 
> file’s nr_file_pages So I want to know how different the 
> /proc/zoneinfo file’s nr_file_pages and /proc/meminfo file’s Cached ?

See the above.

--
Michal Hocko
SUSE Labs