linux-kernel - Re: [PATCH 08/27] staging: lustre: avoid to use bio->bi

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Date:	Mon, 11 Apr 2016 11:30:54 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	James Simmons <jsimmons@...radead.org>
Cc:	Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-block@...r.kernel.org, Boaz Harrosh <boaz@...xistor.com>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Andreas Dilger <andreas.dilger@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"John L. Hammond" <john.hammond@...el.com>,
	Frank Zago <fzago@...y.com>,
	Mike Rapoport <mike.rapoport@...il.com>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	Al Viro <viro@...iv.linux.org.uk>,
	"moderated list:STAGING - LUSTRE PARALLEL FILESYSTEM" 
	<lustre-devel@...ts.lustre.org>,
	"open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>
Subject: Re: [PATCH 08/27] staging: lustre: avoid to use bio->bi_vcnt directly

On Mon, Apr 11, 2016 at 12:02 AM, James Simmons <jsimmons@...radead.org> wrote:
>
>> On Sun, Apr 10, 2016 at 03:37:42PM +0100, James Simmons wrote:
>> >
>> > > The lloop driver should be removed entirely - use the loop driver
>> > > instead.
>> >
>> > I talked with Andreas last week at our annual Lustre users group meeting
>> > about this. The reason I was told for existance is that some users were
>> > using files on a Lustre file system with the loop back device. The
>> > performance was really bad at the time so a lloop was developed to
>> > overcome those limitations. Its been a long time so perhaps its time
>> > to look at the default loop driver again to see if can perform now. If
>> > it doesn't we will go the route of reworking the lloop driver in the
>> > spirit of the cryptoloop device.
>>
>> The loop driver now supports using AIO/DIO on any file systems that
>> implements ->read_iter and ->write_iter. If lustre doesn't support
>> those or doesn't have proper performance using them it should be
>> addressed in the file system.
>>
>> Note that the dio mode in the loop device is not the default and you
>> need to manually enabled it, keep that in mind when testing.
>
> This is excellent news. The only sad thing is that most lustre users
> are running distros that use kernels before the AIO/DIO enhancements
> were landed :-( We will have to keep a copy around for those guys. But
> first I need to test the performance of the loop back driver this
> week before this can be dropped.

Considered that this cleanup patch for lustre loop is quite simple and
straightforward, I suggest to keep this cleanup patch as so and do the
dropping in another patchset. Christoph, are you OK with that?

Thanks,
Ming Lei