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

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Date:	Sun, 5 Jul 2009 23:16:28 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Minchan Kim <minchan.kim@...il.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 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 :)

> 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 ;)

Thanks,
Fengguang
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