Re: 答复: 答复: low memory killer

[Weijie Yang <weijieut@gmail.com>]

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On Thu, Nov 20, 2014 at 8:05 PM, <zhiyuan_zhu@htc.com> wrote:

> 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.
>
>
Why lowmemkiller -total_swapcache_pages()? see commit 058dbde92:

staging: android: lowmemorykiller: neglect swap cached pages in other_file
With ZRAM enabled it is observed that lowmemory killer
doesn't trigger properly. swap cached pages are
accounted in NR_FILE, and lowmemorykiller considers
this as reclaimable and adds to other_file. But these
pages can't be reclaimed unless lowmemorykiller triggers.
So subtract swap pages from other_file.


and commit 31d59a4198f will also make help, please check it.


> 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 18:19
> 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@kroah.com
> 主题: Re: 答复: 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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