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Date:	Tue, 19 May 2009 13:09:32 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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 12:41:38PM +0800, KOSAKI Motohiro wrote:
> Hi
> 
> Thanks for great works.
> 
> 
> > SUMMARY
> > =======
> > The patch decreases the number of major faults from 50 to 3 during 10% cache hot reads.
> > 
> > 
> > SCENARIO
> > ========
> > The test scenario is to do 100000 pread(size=110 pages, offset=(i*100) pages),
> > where 10% of the pages will be activated:
> > 
> >         for i in `seq 0 100 10000000`; do echo $i 110;  done > pattern-hot-10
> >         iotrace.rb --load pattern-hot-10 --play /b/sparse
> 
> 
> Which can I download iotrace.rb?

In the attachment. It relies on some ruby libraries.

> > and monitor /proc/vmstat during the time. The test box has 2G memory.
> > 
> > 
> > ANALYZES
> > ========
> > 
> > I carried out two runs on fresh booted console mode 2.6.29 with the VM_EXEC
> > patch, and fetched the vmstat numbers on
> > 
> > (1) begin:   shortly after the big read IO starts;
> > (2) end:     just before the big read IO stops;
> > (3) restore: the big read IO stops and the zsh working set restored
> > 
> >         nr_mapped   nr_active_file nr_inactive_file       pgmajfault     pgdeactivate           pgfree
> > begin:       2481             2237             8694              630                0           574299
> > end:          275           231976           233914              633           776271         20933042
> > restore:      370           232154           234524              691           777183         20958453
> > 
> > begin:       2434             2237             8493              629                0           574195
> > end:          284           231970           233536              632           771918         20896129
> > restore:      399           232218           234789              690           774526         20957909
> > 
> > and another run on 2.6.30-rc4-mm with the VM_EXEC logic disabled:
> 
> I don't think it is proper comparision.
> you need either following comparision. otherwise we insert many guess into the analysis.
> 
>  - 2.6.29 with and without VM_EXEC patch
>  - 2.6.30-rc4-mm with and without VM_EXEC patch

I think it doesn't matter that much when it comes to "relative" numbers.
But anyway I guess you want to try a more typical desktop ;)
Unfortunately currently the Xorg is broken in my test box..

> > 
> > begin:       2479             2344             9659              210                0           579643
> > end:          284           232010           234142              260           772776         20917184
> > restore:      379           232159           234371              301           774888         20967849
> > 
> > The numbers show that
> > 
> > - The startup pgmajfault of 2.6.30-rc4-mm is merely 1/3 that of 2.6.29.
> >   I'd attribute that improvement to the mmap readahead improvements :-)
> > 
> > - The pgmajfault increment during the file copy is 633-630=3 vs 260-210=50.
> >   That's a huge improvement - which means with the VM_EXEC protection logic,
> >   active mmap pages is pretty safe even under partially cache hot streaming IO.
> > 
> > - when active:inactive file lru size reaches 1:1, their scan rates is 1:20.8
> >   under 10% cache hot IO. (computed with formula Dpgdeactivate:Dpgfree)
> >   That roughly means the active mmap pages get 20.8 more chances to get
> >   re-referenced to stay in memory.
> > 
> > - The absolute nr_mapped drops considerably to 1/9 during the big IO, and the
> >   dropped pages are mostly inactive ones. The patch has almost no impact in
> >   this aspect, that means it won't unnecessarily increase memory pressure.
> >   (In contrast, your 20% mmap protection ratio will keep them all, and
> >   therefore eliminate the extra 41 major faults to restore working set
> >   of zsh etc.)
> 
> I'm surprised this.
> Why your patch don't protect mapped page from streaming io?

It is only protecting the *active* mapped pages, as expected.
But yes, the active percent is much lower than expected :-)

> I strongly hope reproduce myself, please teach me reproduce way.

OK. 

Firstly:

         for i in `seq 0 100 10000000`; do echo $i 110;  done > pattern-hot-10
         dd if=/dev/zero of=/tmp/sparse bs=1M count=1 seek=1024000

Then boot into desktop and run concurrently:

         iotrace.rb --load pattern-hot-10 --play /tmp/sparse
         vmmon  nr_mapped nr_active_file nr_inactive_file   pgmajfault pgdeactivate pgfree

Note that I was creating the sparse file in btrfs, which happens to be
very slow in sparse file reading:

        151.194384MB/s 284.198252s 100001x 450560b --load pattern-hot-10 --play /b/sparse

In that case, the inactive list is rotated at the speed of 250MB/s,
so a full scan of which takes about 3.5 seconds, while a full scan
of active file list takes about 77 seconds.

Attached source code for both of the above tools.

Thanks,
Fengguang

Download attachment "iotrace.rb" of type "application/x-ruby" (8575 bytes)

View attachment "vmmon.c" of type "text/x-csrc" (2411 bytes)

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