linux-kernel - Re: RFC: dirty

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Message-ID: <20100521160014.GC3412@quack.suse.cz>
Date:	Fri, 21 May 2010 18:00:14 +0200
From:	Jan Kara <jack@...e.cz>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Zan Lynx <zlynx@....org>, lwoodman@...hat.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Nick Piggin <npiggin@...e.de>,
	Jan Kara <jack@...e.cz>
Subject: Re: RFC: dirty_ratio back to 40%

On Fri 21-05-10 10:11:59, KOSAKI Motohiro wrote:
> > > So, I'd prefer to restore the default rather than both Redhat and SUSE apply exactly
> > > same distro specific patch. because we can easily imazine other users will face the same
> > > issue in the future.
> > 
> > On desktop systems the low dirty limits help maintain interactive feel. 
> > Users expect applications that are saving data to be slow. They do not 
> > like it when every application in the system randomly comes to a halt 
> > because of one program stuffing data up to the dirty limit.
> 
> really?
> Do you mean our per-task dirty limit wouldn't works?
> 
> If so, I think we need fix it. IOW sane per-task dirty limitation seems
> independent issue from per-system dirty limit.
  Well, I don't know about any per-task dirty limits. What function
implements them? Any application that dirties a single page can be caught
and forced to call balance_dirty_pages() and do writeback.
  But generally what we observe on a desktop with lots of dirty memory is
that application needs to allocate memory (either private one or for page
cache) and that triggers direct reclaim so the allocation takes a long
time to finish and thus the application is sluggish...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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