linux-kernel - Re: per-bdi-throttling: synchronous writepage doesn't work correctly

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Message-Id: <E1IndPT-00047e-00@dorka.pomaz.szeredi.hu>
Date:	Thu, 01 Nov 2007 18:00:47 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	a.p.zijlstra@...llo.nl
CC:	jdike@...toit.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: per-bdi-throttling: synchronous writepage doesn't work
	correctly

> > Hi,
> > 
> > It looks like bdi_thresh will always be zero if filesystem does
> > synchronous writepage, resulting in very poor write performance.
> > 
> > Hostfs (UML) is one such example, but there might be others.
> > 
> > The only solution I can think of is to add a set_page_writeback();
> > end_page_writeback() pair (or some reduced variant, that only does
> > the proportions magic).  But that means auditing quite a few
> > filesystems...
> 
> Ouch...
> 
> I take it there is no other function that is shared between all these
> writeout paths which we could stick a bdi_writeout_inc(bdi) in?

No, and you can't detect it from the callers either I think.

Miklos
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