linux-kernel - Re: [PATCH 5/5] add NR_ANON

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Date:	Mon, 6 Jul 2009 00:27:20 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 5/5] add NR_ANON_PAGES to OOM log

On Mon, Jul 6, 2009 at 12:16 AM, Wu Fengguang<fengguang.wu@...el.com> wrote:
> On Sun, Jul 05, 2009 at 11:04:17PM +0800, Minchan Kim wrote:
>> On Sun, Jul 5, 2009 at 10:19 PM, KOSAKI
>> Motohiro<kosaki.motohiro@...fujitsu.com> wrote:
>> >>> > > + printk("%ld total anon pages\n", global_page_state(NR_ANON_PAGES));
>> >>> > >   printk("%ld total pagecache pages\n", global_page_state(NR_FILE_PAGES));
>> >>> >
>> >>> > Can we put related items together, ie. this looks more friendly:
>> >>> >
>> >>> >         Anon:XXX active_anon:XXX inactive_anon:XXX
>> >>> >         File:XXX active_file:XXX inactive_file:XXX
>> >>>
>> >>> hmmm. Actually NR_ACTIVE_ANON + NR_INACTIVE_ANON != NR_ANON_PAGES.
>> >>> tmpfs pages are accounted as FILE, but it is stay in anon lru.
>> >>
>> >> Right, that's exactly the reason I propose to put them together: to
>> >> make the number of tmpfs pages obvious.
>> >>
>> >>> I think your proposed format easily makes confusion. this format cause to
>> >>> imazine Anon = active_anon + inactive_anon.
>> >>
>> >> Yes it may confuse normal users :(
>> >>
>> >>> At least, we need to use another name, I think.
>> >>
>> >> Hmm I find it hard to work out a good name.
>> >>
>> >> But instead, it may be a good idea to explicitly compute the tmpfs
>> >> pages, because the excessive use of tmpfs pages could be a common
>> >> reason of OOM.
>> >
>> > Yeah,  explicite tmpfs/shmem accounting is also useful for /proc/meminfo.
>>
>> Do we have to account it explicitly?
>
> When OOM happens, one frequent question to ask is: are there too many
> tmpfs/shmem pages?  Exporting this number makes our oom-message-decoding
> life easier :)

Indeed.

>> If we know the exact isolate pages of each lru,
>>
>> tmpfs/shmem = (NR_ACTIVE_ANON + NR_INACTIVE_ANON + isolate(anon)) -
>> NR_ANON_PAGES.
>>
>> Is there any cases above equation is wrong ?
>
> That's right, but the calculation may be too complex (and boring) for
> our little brain ;)

Yes. if something is change in future or we miss someting, the above
question may be wrong.
I wanted to remove overhead of new accouting.

Anyway, I think it's not a big cost in normal system.
So If you want to add new accounting, I don't have any objection. :)

> Thanks,
> Fengguang
>



-- 
Kind regards,
Minchan Kim
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