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 21:37:47 +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 09:19 PM, Dave Kleikamp wrote:
>> 1. Could we use fdatasync there? (otherwise it can hurt performance very
>> badly)
> I don't see why not.
Great.

>> 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?
> If more than one REQ_FLUSH bio is in the list, they should be performed
> in order. We must call vfs_fsync() between each of them to guarantee that.
yes, my bad

> A less complex tradeoff would be to move the vfs_fsync() call to
> loop_make_request() so it is called in the context of the thread making
> the request. That would make those threads requesting ordered IO to pay
> the price while others would be able to proceed.
>
> This is something I can re-visit. I don't want to hold up progress on
> the patchset for something that can be improved later.
Completely agree, it can be done later.

Thanks,
Maxim

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