答复: 答复: low memory killer

[<zhiyuan_zhu@htc.com>]

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Hi Greg/Michal
Very sorry I have a mistake in previous mail. (It should be nr_file_pages not nr_free_pages)
I rearrange this problem.

// *********** log begin **********
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
//  **** /proc/meminfo 's result
4      161030.084797       2014-11-07 21:44:53.304        Cached:           142448 kB
// *********** log end **********

After I checked the android's low memory strategy: kernel/drivers/staging/android/lowmemorykiller.c

// ****** code begin *********
		other_file = global_page_state(NR_FILE_PAGES) -
						global_page_state(NR_SHMEM) -
						total_swapcache_pages();

		lowmem_print(1, "Killing '%s' (%d), adj %hd,\n" \
				"   to free %ldkB on behalf of '%s' (%d) because\n" \
				"   cache %ldkB is below limit %ldkB for oom_score_adj %hd\n" \
				"   Free memory is %ldkB above reserved\n",
			     selected->comm, selected->pid,
			     selected_oom_score_adj,
			     selected_tasksize * (long)(PAGE_SIZE / 1024),
			     current->comm, current->pid,
			     other_file * (long)(PAGE_SIZE / 1024),
			     minfree * (long)(PAGE_SIZE / 1024),
			     min_score_adj,
			     other_free * (long)(PAGE_SIZE / 1024));
// ******* code end ************

So android's strategy's free memory is = other_file = (nr file pages - nr shmem - total swapcache pages) * 4K = [cache 72460kB]
But the system's free memory is: Cached:        142448 kB  // from /proc/meminfo

And system's free memory is: Cached + MemFree + Buffers is largely than the memory which anroid lowmemorykiller calculated memory [cache 72460K]
At this time point, system will kill some important processes, but system have enough memory.
This is android's lowmemorykiller defect? or Linux kernel memory's defect?

So I have some questions:
I have a question: what's the nr file pages mean? What different between nr_file_pages from Cached (from /proc/meminfo)?
And nr shmem, swapcache pages are small, so I think this is the key problem why android's stragegy calculated free memory is largely less than /proc/meminfo Cached's value.

Thanks
Zhiyuan zhu

-----ÓʼþÔ­¼þ-----
·¢¼þÈË: Michal Hocko [mailto:mhocko@suse.cz] 
·¢ËÍʱ¼ä: 2014Äê11ÔÂ20ÈÕ 18:19
ÊÕ¼þÈË: Zhiyuan Zhu(ÖìÖ¾ßh)
³­ËÍ: hannes@cmpxchg.org; Future Zhou(ÖÜδí); Rachel Zhang(ˆ¬“); bsingharora@gmail.com; kamezawa.hiroyu@jp.fujitsu.com; cgroups@vger.kernel.org; linux-mm@kvack.org; greg@kroah.com
Ö÷Ìâ: Re: ´ð¸´: low memory killer

On Thu 20-11-14 10:09:25, zhiyuan_zhu@htc.com wrote:
> 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.

nr_free_pages refers to pages which are not allocated. Cached referes to a used memory which is easily reclaimable so it can be reused should there be a need and free memory drops down. So this is a normal situation. How is this related to the lowmemory killer question posted previously?

[...]
--
Michal Hocko
SUSE Labs

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