linux-kernel - Re: I/O blocked while dirty pages are being flushed

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Date:	Mon, 25 Mar 2013 08:31:43 +0100 (CET)
From:	Fredrik Tolf <fredrik@...da2000.com>
To:	Bart Van Assche <bvanassche@....org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: I/O blocked while dirty pages are being flushed

On Sun, 24 Mar 2013, Bart Van Assche wrote:
> On 03/24/13 06:12, Fredrik Tolf wrote:
>> While this flush is running, I find that many a process goes into disk
>> sleep waiting for the flush to complete. This includes the process
>> manipulating the mmapped file whenever it tries to redirty a page
>> currently waiting to be flushed, but also, for instance, programs that
>> write() to log files (since, I guess, the buffer page backing the last
>> written portion of the log file is being flushed).
>
> Had you already encountered this article: Jonathan Corbet, The trouble with 
> stable pages, March 13, 2012 (http://lwn.net/Articles/486311/) ?

I had not, but that certainly does seem to be the exact problem I'm 
having. Thanks for the link; it was a very interesting read! Does anyone 
know if any progress has been made since about any resolution of the 
situation?

I notice linked mail threads with people saying that they have simply 
removed the calls to wait_on_page_writeback to resolve their problems. Can 
this still be considered safe, or have other systems than this 
block-device checksumming started depending on stable pages since? Like 
software RAID, for instance?

--

Fredrik Tolf
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