Subject: Re: [patch] use cheaper elv_queue_empty when unplug a device
From: Arjan van de Ven <arjan@infradead.org>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Jens Axboe <axboe@suse.de>, "Chen, Kenneth W" <kenneth.w.chen@intel.com>,
       linux-kernel@vger.kernel.org
In-Reply-To: <42491DBE.6020303@yahoo.com.au>
References: <200503290253.j2T2rqg25691@unix-os.sc.intel.com>
	 <20050329080646.GE16636@suse.de>  <42491DBE.6020303@yahoo.com.au>
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Date: Tue, 29 Mar 2005 12:10:25 +0200
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On Tue, 2005-03-29 at 19:19 +1000, Nick Piggin wrote:
> - removes the relock/retry merge mechanism in __make_request if we
>    aren't able to get the GFP_ATOMIC allocation. Just fall through
>    and assume the chances of getting a merge will be small (is this
>    a valid assumption? Should measure it I guess).

this may have a potential problem; if the vm gets in trouble, you
suddenly start to generate worse IO patterns, which means IO performance
goes down right when it's most needed.....

of course we need to figure if this actually ever hits in practice,
because if it doesn't I'm all for simpler code.


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