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

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Message-Id: <E1InfZx-0004Eu-00@dorka.pomaz.szeredi.hu>
Date:	Thu, 01 Nov 2007 20:19:45 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	peterz@...radead.org
CC:	jdike@...toit.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	akpm@...ux-foundation.org, viro@...iv.linux.org.uk
Subject: Re: per-bdi-throttling: synchronous writepage doesn't work
	correctly

> > 
> >       See the file "Locking" for more details.
> > 
> > 
> > The "should set PG_Writeback" bit threw me off I guess.
> 
> Hmm, set_page_writeback() is also the one clearing the radix tree dirty
> tag. So if that is not called, we get in a bit of a mess, no?
> 
> Which makes me think hostfs is buggy.

Yes, looks like that sort of usage is not valid.  But not clearing the
dirty tag won't cause any malfunction, it'll just waste some CPU when
looking for dirty pages to write back.  This is probably why this
wasn't noticed earlier.

Miklos
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