From: Jan Kara <jack@suse.cz>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: lwoodman@redhat.com, LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>, Nick Piggin <npiggin@suse.de>,
Jan Kara <jack@suse.cz>
Subject: Re: RFC: dirty_ratio back to 40%
Date: Fri, 21 May 2010 17:50:59 +0200 [thread overview]
Message-ID: <20100521155059.GB3412@quack.suse.cz> (raw)
In-Reply-To: <20100521083408.1E36.A69D9226@jp.fujitsu.com>
Hi,
On Fri 21-05-10 08:48:57, KOSAKI Motohiro wrote:
> CC to Nick and Jan
Thanks.
> > We've seen multiple performance regressions linked to the lower(20%)
> > dirty_ratio. When performing enough IO to overwhelm the background
> > flush daemons the percent of dirty pagecache memory quickly climbs
> > to the new/lower dirty_ratio value of 20%. At that point all writing
> > processes are forced to stop and write dirty pagecache pages back to disk.
> > This causes performance regressions in several benchmarks as well as causing
> > a noticeable overall sluggishness. We all know that the dirty_ratio is
> > an integrity vs performance trade-off but the file system journaling
> > will cover any devastating effects in the event of a system crash.
> >
> > Increasing the dirty_ratio to 40% will regain the performance loss seen
> > in several benchmarks. Whats everyone think about this???
>
> In past, Jan Kara also claim the exactly same thing.
>
> Subject: [LSF/VM TOPIC] Dynamic sizing of dirty_limit
> Date: Wed, 24 Feb 2010 15:34:42 +0100
>
> > (*) We ended up increasing dirty_limit in SLES 11 to 40% as it used to be
> > with old kernels because customers running e.g. LDAP (using BerkelyDB
> > heavily) were complaining about performance problems.
>
> So, I'd prefer to restore the default rather than both Redhat and SUSE apply exactly
> same distro specific patch. because we can easily imazine other users will face the same
> issue in the future.
>
> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>
> Nick, Jan, if the above is too old and your distro have been dropped the patch, please
> correct me.
No, SLE11 SP1 still has a patch that increases dirty_ratio to 40. But on
the other hand I agree with Zan that for desktop, 40% of memory for dirty
data is a lot these days and takes a long time to write out (it could
easily be 30s - 1m). On a desktop the memory is much better used as
a read-only pagecache or for memory hungry apps like Firefox or Acrobat
Reader. So I believe for a desktop the current setting (20) is a better
choice. So until we find a way how to dynamically size the dirty limit, we
have to decide whether we want to have a default setting for a server or
for a desktop... Personally, I don't care very much and I feel my time
would be better spent thinking about dynamic limit sizing rather than
arguing what is better default ;).
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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next prev parent reply other threads:[~2010-05-21 15:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-20 11:20 RFC: dirty_ratio back to 40% Larry Woodman
2010-05-20 12:29 ` Heinz Diehl
2010-05-20 13:47 ` Richard Kennedy
2010-05-20 23:48 ` KOSAKI Motohiro
2010-05-21 0:48 ` Zan Lynx
2010-05-21 1:11 ` KOSAKI Motohiro
2010-05-21 16:00 ` Jan Kara
2010-05-24 19:50 ` Ric Wheeler
2010-05-21 15:50 ` Jan Kara [this message]
2010-05-21 6:18 ` David Miller
2010-06-08 18:49 ` Christoph Hellwig
2010-06-08 19:01 ` Larry Woodman
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