Subject: Re: Likley stupid question on "throttle_vm_writeout"
From: Peter Zijlstra <peterz@infradead.org>
To: Martin Knoblauch <spamtrap@knobisoft.de>
Cc: linux-kernel@vger.kernel.org, Fengguang Wu <wfg@mail.ustc.edu.cn>
In-Reply-To: <799070.68490.qm@web32608.mail.mud.yahoo.com>
References: <799070.68490.qm@web32608.mail.mud.yahoo.com>
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Date: Mon, 09 Nov 2009 16:26:33 +0100
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On Mon, 2009-11-09 at 07:15 -0800, Martin Knoblauch wrote:
> Hi, (please CC me on replies)
> 
>  I have a likely stupid question on the function "throttle_vm_writeout". Looking at the code I find:
> 
>                 if (global_page_state(NR_UNSTABLE_NFS) +
>                         global_page_state(NR_WRITEBACK) <= dirty_thresh)
>                                 break;
>                 congestion_wait(WRITE, HZ/10);
> 
> Shouldn't the NR_FILE_DIRTY pages be considered as well?

Ha, you just trod onto a piece of ugly I'd totally forgotten about ;-)

The intent of throttle_vm_writeout() is to limit the total pages in
writeout and to wait for them to go-away.

Everybody hates the function, nobody managed to actually come up with
anything better.

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