linux-kernel - Re: BLK_MQ_F_DEFER

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Message-ID: <55352238.1020301@kernel.dk>
Date:	Mon, 20 Apr 2015 09:58:48 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Jeff Moyer <jmoyer@...hat.com>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: BLK_MQ_F_DEFER_ISSUE

On 04/20/2015 09:09 AM, Jeff Moyer wrote:
> Hi, Jens,
>
> This flag was introduced under the auspices that the nvme blk-mq
> conversion would make use of it.  That never materialized.  Are there
> still plans to make use of it?  If not, I'd like to get rid of it.  If
> so, then let's document it better.

Yep I still want to use it, and I do have a patch that uses it as well 
that I've run through testing. I thought I had pushed it somewhere, but 
it doesn't seem like I have. I just wanted to get the lower hanging 
optimizations out there first, like the kmalloc/kfree and 
queue-lock-for-completions removal. Former is in, latter is not yet.

It's a useful optimization for lots of cases and I'm sure it'll see 
other uses, once the nvme patch is in. That will give people a reference 
point.

-- 
Jens Axboe

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