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

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Message-Id: <E1IndEw-00046x-00@dorka.pomaz.szeredi.hu>
Date:	Thu, 01 Nov 2007 17:49:54 +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: 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...

Miklos
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