linux-kernel - Re: [PATCH 10/10] mm: per device dirty threshold

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Date:	Tue, 24 Apr 2007 03:00:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	a.p.zijlstra@...llo.nl, neilb@...e.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, dgc@....com,
	tomoki.sekiyama.qu@...achi.com, nikita@...sterfs.com,
	trond.myklebust@....uio.no, yingchao.zhou@...il.com
Subject: Re: [PATCH 10/10] mm: per device dirty threshold

On Tue, 24 Apr 2007 11:47:20 +0200 Miklos Szeredi <miklos@...redi.hu> wrote:

> > Ahh, now I see; I had totally blocked out these few lines:
> > 
> > 			pages_written += write_chunk - wbc.nr_to_write;
> > 			if (pages_written >= write_chunk)
> > 				break;		/* We've done our duty */
> > 
> > yeah, those look dubious indeed... And reading back Neil's comments, I
> > think he agrees.
> > 
> > Shall we just kill those?
> 
> I think we should.
> 
> Athough I'm a little afraid, that Akpm will tell me again, that I'm a
> stupid git, and that those lines are in fact vitally important ;)
> 

It depends what they're replaced with.

That code is there, iirc, to prevent a process from getting stuck in
balance_dirty_pages() forever due to the dirtying activity of other
processes.

hm, we ask the process to write write_chunk pages each go around the loop.
So if it wrote write-chunk/2 pages on the first pass it might end up writing
write_chunk*1.5 pages total.  I guess that's rare and doesn't matter much
if it does happen - the upper bound is write_chunk*2-1, I think.
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