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

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Message-ID: <x49mx66whty.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 20 Apr 2012 11:20:25 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Dave Kleikamp <dave.kleikamp@...cle.com>
Cc:	"Maxim V. Patlasov" <mpatlasov@...allels.com>,
	"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel\@vger.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

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.

Cheers,
Jeff
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