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

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Message-ID: <20110810032954.GC24486@localhost>
Date:	Wed, 10 Aug 2011 11:29:54 +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 Wed, Aug 10, 2011 at 01:46:21AM +0800, Vivek Goyal wrote:
> On Sat, Aug 06, 2011 at 04:44:51PM +0800, Wu Fengguang wrote:
> 
> [..]
> >   * balance_dirty_pages() must be called by processes which are generating dirty
> >   * data.  It looks at the number of dirty pages in the machine and will force
> >   * the caller to perform writeback if the system is over `vm_dirty_ratio'.
> > @@ -1008,6 +1005,9 @@ static void balance_dirty_pages(struct a
> >  	if (clear_dirty_exceeded && bdi->dirty_exceeded)
> >  		bdi->dirty_exceeded = 0;
> >  
> > +	current->nr_dirtied = 0;
> > +	current->nr_dirtied_pause = ratelimit_pages(nr_dirty, dirty_thresh);
> > +
> >  	if (writeback_in_progress(bdi))
> >  		return;
> >  
> > @@ -1034,8 +1034,6 @@ void set_page_dirty_balance(struct page 
> >  	}
> >  }
> >  
> > -static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
> > -
> >  /**
> >   * balance_dirty_pages_ratelimited_nr - balance dirty memory state
> >   * @mapping: address_space which was dirtied
> > @@ -1055,30 +1053,17 @@ void balance_dirty_pages_ratelimited_nr(
> >  {
> >  	struct backing_dev_info *bdi = mapping->backing_dev_info;
> >  	unsigned long ratelimit;
> > -	unsigned long *p;
> >  
> >  	if (!bdi_cap_account_dirty(bdi))
> >  		return;
> >  
> > -	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));

Thanks,
Fengguang
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