linux-kernel - Re: [PATCH 2/3] vmscan: make mapped executable pages the first class citizen

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Date:	Wed, 20 May 2009 10:59:05 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Christoph Lameter <cl@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Elladan <elladan@...imo.com>, Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>
Subject: Re: [PATCH 2/3] vmscan: make mapped executable pages the first class  citizen

> On Tue, May 19, 2009 at 08:28:28PM +0800, KOSAKI Motohiro wrote:
> > Hi
> > 
> > 2009/5/19 Wu Fengguang <fengguang.wu@...el.com>:
> > > On Tue, May 19, 2009 at 04:06:35PM +0800, KOSAKI Motohiro wrote:
> > >> > > > Like the console mode, the absolute nr_mapped drops considerably - to 1/13 of
> > >> > > > the original size - during the streaming IO.
> > >> > > >
> > >> > > > The delta of pgmajfault is 3 vs 107 during IO, or 236 vs 393 during the whole
> > >> > > > process.
> > >> > >
> > >> > > hmmm.
> > >> > >
> > >> > > about 100 page fault don't match Elladan's problem, I think.
> > >> > > perhaps We missed any addional reproduce condition?
> > >> >
> > >> > Elladan's case is not the point of this test.
> > >> > Elladan's IO is use-once, so probably not a caching problem at all.
> > >> >
> > >> > This test case is specifically devised to confirm whether this patch
> > >> > works as expected. Conclusion: it is.
> > >>
> > >> Dejection ;-)
> > >>
> > >> The number should address the patch is useful or not. confirming as expected
> > >> is not so great.
> > >
> > > OK, let's make the conclusion in this way:
> > >
> > > The changelog analyzed the possible beneficial situation, and this
> > > test backs that theory with real numbers, ie: it successfully stops
> > > major faults when the active file list is slowly scanned when there
> > > are partially cache hot streaming IO.
> > >
> > > Another (amazing) finding of the test is, only around 1/10 mapped pages
> > > are actively referenced in the absence of user activities.
> > >
> > > Shall we protect the remaining 9/10 inactive ones? This is a question ;-)
> > 
> > Unfortunately, I don't reproduce again.
> > I don't apply your patch yet. but mapped ratio is reduced only very little.
> 
> mapped ratio or absolute numbers? The ratio wont change much because
> nr_mapped is already small.

My box is running Fedora 10 initlevel 5 (GNOME desktop).

many GNOME component is mapped very many process (likes >50).
Thus, these page aren't dropped by typical any workload.



> > I think smem can show which library evicted.  Can you try it?
> > 
> > download:  http://www.selenic.com/smem/
> > usage:   ./smem -m -r --abbreviate
> 
> Sure, but I don't see much change in its output (see attachments).
> 
> smem-console-0 is collected after fresh boot,
> smem-console-1 is collected after the big IO.

hmmmm, your result has following characatistics.

- no graphics component
- very few mapped library
  (it is almost only zsh library)

Can you try test on X environment?



> > We can't decide 9/10 is important or not. we need know actual evicted file list.
> 
> Right. But what I measured is the activeness. Almost zero major page
> faults means the evicted 90% mapped pages are inactive during the
> long 300 seconds of IO.

Agreed.
IOW, I don't think your test environment is typical desktop...




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