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Message-ID: <20090519050932.GB8769@localhost>
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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