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

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Message-ID: <4F917C2F.4020805@oracle.com>
Date:	Fri, 20 Apr 2012 10:09:35 -0500
From:	Dave Kleikamp <dave.kleikamp@...cle.com>
To:	"Maxim V. Patlasov" <mpatlasov@...allels.com>
CC:	"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 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
also guarantees that previous writes make it to media before the current
write, so it looks like I need to add an explicit vfs_fsync() in the new
path (conditional on REQ_FLUSH of course).

Zach, thoughts?

Shaggy

> 
> Thanks,
> Maxim
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