linux-kernel - Re: [RFC PATCH v2 15/21] loop: use aio to perform io on the underlying file

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Message-ID: <4F918B66.10107@oracle.com>
Date:	Fri, 20 Apr 2012 11:14:30 -0500
From:	Dave Kleikamp <dave.kleikamp@...cle.com>
To:	Jeff Moyer <jmoyer@...hat.com>
CC:	"Maxim V. Patlasov" <mpatlasov@...allels.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Zach Brown <zab@...bo.net>
Subject: Re: [RFC PATCH v2 15/21] loop: use aio to perform io on the underlying
 file



On 04/20/2012 10:20 AM, Jeff Moyer wrote:
> Dave Kleikamp <dave.kleikamp@...cle.com> writes:
> 
>> On 04/20/2012 09:48 AM, Maxim V. Patlasov wrote:
>>> On 03/30/2012 07:43 PM, Dave Kleikamp wrote:
>>>> From: Zach Brown<zab@...bo.net>
>>>>
>>>> This uses the new kernel aio interface to process loopback IO by
>>>> submitting concurrent direct aio.  Previously loop's IO was serialized
>>>> by synchronous processing in a thread.
>>>>
>>>
>>> The patch ignores REQ_FLUSH bit of bi_rw. Is it simply overlook?
>>
>> Good question. Since the loop device is sending only direct IO requests,
>> it shouldn't be necessary to explicitly flush page cache, but REQ_FLUSH
> 
> REQ_FLUSH isn't about the page cache, it's about flushing the volatile
> disk write cache.  You need to handle that.

Yeah, and looking again at this code, I need to handle REQ_DISCARD as well.

> 
> Cheers,
> Jeff
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