linux-kernel - Re: RFC: dirty

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Message-Id: <1276023684.8736.51.camel@dhcp-100-19-198.bos.redhat.com>
Date:	Tue, 08 Jun 2010 15:01:24 -0400
From:	Larry Woodman <lwoodman@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>
Subject: Re: RFC: dirty_ratio back to 40%

On Tue, 2010-06-08 at 14:49 -0400, Christoph Hellwig wrote:
> Did this patch get merged somewhere?

I dont think it ever did, about 1/2 of responses were for it and the
other 1/2 against it.

Larry

> 
> On Thu, May 20, 2010 at 07:20:42AM -0400, Larry Woodman wrote:
> > 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???
> > 
> > 
> > 
> > 
> > 
> > ------------------------------------------------------------------------
> > 
> > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > index ef27e73..645a462 100644
> > --- a/mm/page-writeback.c
> > +++ b/mm/page-writeback.c
> > @@ -78,7 +78,7 @@ int vm_highmem_is_dirtyable;
> > /*
> >  * The generator of dirty data starts writeback at this percentage
> >  */
> > -int vm_dirty_ratio = 20;
> > +int vm_dirty_ratio = 40;
> > 
> > /*
> >  * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
> > 
> > --
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