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

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Date:	Fri, 20 Apr 2012 20:14:28 +0400
From:	"Maxim V. Patlasov" <mpatlasov@...allels.com>
To:	Dave Kleikamp <dave.kleikamp@...cle.com>
CC:	Zach Brown <zab@...bo.net>, Jeff Moyer <jmoyer@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 15/21] loop: use aio to perform io on the underlying
 file

On 04/20/2012 07:57 PM, Dave Kleikamp wrote:
>> So yeah, I'd agree that the loop code should be reworked a bit so that
>> both the filebacked and aio methods call vfs_sync() when they see
>> REQ_FLUSH.
> It's an easy fix. I don't anticipate that it will hurt performance too
> badly.

Two questions:

1. Could we use fdatasync there? (otherwise it can hurt performance very 
badly)

2. vfs_sync() is synchronous. loop_thread() will be blocked till it's 
completed. Would it be better to perform vfs_sync in another thread (to 
allow other bio-s in loop queue proceed)? Also, if there are more than 
one REQ_FLUSH bio in lo->lo_bio_list, we could call vfs_sync() only 
once. Make sense?

Thanks,
Maxim
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