linux-kernel - Re: [PATCH 4/5] writeback: per task dirty rate limit

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Date:	Thu, 11 Aug 2011 08:55:39 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrea Righi <arighi@...eler.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] writeback: per task dirty rate limit

On Thu, Aug 11, 2011 at 02:18:54AM +0800, Vivek Goyal wrote:
> On Wed, Aug 10, 2011 at 11:29:54AM +0800, Wu Fengguang wrote:
> 
> [..]
> > > > -	ratelimit = ratelimit_pages;
> > > > -	if (mapping->backing_dev_info->dirty_exceeded)
> > > > +	ratelimit = current->nr_dirtied_pause;
> > > > +	if (bdi->dirty_exceeded)
> > > >  		ratelimit = 8;
> > > 
> > > Should we make sure that ratelimit is more than 8? It could be that
> > > ratelimit is 1 and we set it higher (just reverse of what we wanted?)
> > 
> > Good catch! I actually just fixed it in that direction :)
> > 
> >         if (bdi->dirty_exceeded)
> > -               ratelimit = 8;
> > +               ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
> 
> With page size 64K, will above lead to retelimit 0? Is that what you want.
> I wouldn't think so.

Yeah, it looks a bit weird.. however ratelimit=0 would behave the
same with ratelimit=1 because balance_dirty_pages_ratelimited_nr()
is always called with (nr_pages_dirtied >= 1).

Thanks,
Fengguang
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