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From: Richard Kennedy <richard@rsk.demon.co.uk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Wu Fengguang <fengguang.wu@intel.com>,
	lkml <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [RFC PATCH] mm: let the bdi_writeout fraction respond more quickly
Date: Thu, 17 Jun 2010 12:39:56 +0100	[thread overview]
Message-ID: <1276774796.1978.11.camel@castor.rsk> (raw)
In-Reply-To: <1276714466.1745.625.camel@laptop>

On Wed, 2010-06-16 at 20:54 +0200, Peter Zijlstra wrote:
> On Mon, 2010-06-14 at 15:44 +0100, Richard Kennedy wrote:
> > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > > index 2fdda90..315dd04 100644
> > > --- a/mm/page-writeback.c
> > > +++ b/mm/page-writeback.c
> > > @@ -144,7 +144,7 @@ static int calc_period_shift(void)
> > >       else
> > >               dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
> > >                               100;
> > > -     return 2 + ilog2(dirty_total - 1);
> > > +     return ilog2(dirty_total - 1) - 4;
> > >  } 
> 
> IIRC I suggested similar things in the past and all we needed to do was
> find people doing the measurements on different bits of hardware or so..
> 
> I don't have any problems with the approach, all we need to make sure is
> that we never return 0 or a negative number (possibly ensure a minimum
> positive shift value).

Yep that sounds reasonable. would minimum shift of 4 be ok ?

something like

	max ( (ilog2(dirty_total - 1)- 4) , 4);

Unfortunately volunteers don't seem to be leaping out of the woodwork,
maybe Andrew could be persuaded to try this in his tree for a while and
see if any one squeaks ?

regards
Richard


WARNING: multiple messages have this Message-ID (diff)
From: Richard Kennedy <richard@rsk.demon.co.uk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Wu Fengguang <fengguang.wu@intel.com>,
	lkml <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [RFC PATCH] mm: let the bdi_writeout fraction respond more quickly
Date: Thu, 17 Jun 2010 12:39:56 +0100	[thread overview]
Message-ID: <1276774796.1978.11.camel@castor.rsk> (raw)
In-Reply-To: <1276714466.1745.625.camel@laptop>

On Wed, 2010-06-16 at 20:54 +0200, Peter Zijlstra wrote:
> On Mon, 2010-06-14 at 15:44 +0100, Richard Kennedy wrote:
> > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > > index 2fdda90..315dd04 100644
> > > --- a/mm/page-writeback.c
> > > +++ b/mm/page-writeback.c
> > > @@ -144,7 +144,7 @@ static int calc_period_shift(void)
> > >       else
> > >               dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
> > >                               100;
> > > -     return 2 + ilog2(dirty_total - 1);
> > > +     return ilog2(dirty_total - 1) - 4;
> > >  } 
> 
> IIRC I suggested similar things in the past and all we needed to do was
> find people doing the measurements on different bits of hardware or so..
> 
> I don't have any problems with the approach, all we need to make sure is
> that we never return 0 or a negative number (possibly ensure a minimum
> positive shift value).

Yep that sounds reasonable. would minimum shift of 4 be ok ?

something like

	max ( (ilog2(dirty_total - 1)- 4) , 4);

Unfortunately volunteers don't seem to be leaping out of the woodwork,
maybe Andrew could be persuaded to try this in his tree for a while and
see if any one squeaks ?

regards
Richard

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  reply	other threads:[~2010-06-17 11:40 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-06-14 13:58 [RFC PATCH] mm: let the bdi_writeout fraction respond more quickly Richard Kennedy
2010-06-14 14:44 ` Richard Kennedy
2010-06-14 14:44   ` Richard Kennedy
2010-06-16 18:54   ` Peter Zijlstra
2010-06-16 18:54     ` Peter Zijlstra
2010-06-17 11:39     ` Richard Kennedy [this message]
2010-06-17 11:39       ` Richard Kennedy
2010-06-17 11:41       ` Jens Axboe
2010-06-17 11:41         ` Jens Axboe
2010-06-17 18:45         ` Richard Kennedy
2010-06-17 18:45           ` Richard Kennedy

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