linux-ext4 - Re: [PATCH 5/8] nowait aio: return on congested block device

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Date:   Wed, 8 Mar 2017 16:28:06 +0100
From:   Jan Kara <jack@...e.cz>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc:     Sagi Grimberg <sagi@...mberg.me>, jack@...e.com, hch@...radead.org,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: Re: [PATCH 5/8] nowait aio: return on congested block device

On Wed 08-03-17 09:00:09, Goldwyn Rodrigues wrote:
> 
> 
> On 03/08/2017 01:03 AM, Sagi Grimberg wrote:
> > 
> >> -        if (likely(blk_queue_enter(q, false) == 0)) {
> >> +        if (likely(blk_queue_enter(q, bio_flagged(bio, BIO_NOWAIT))
> >> == 0)) {
> >>              ret = q->make_request_fn(q, bio);
> > 
> > I think that for ->make_request to not block we'd need to set
> > BLK_MQ_REQ_NOWAIT in blk_mq_alloc_data to avoid blocking on a tag
> > allocation.
> > 
> > Something like the untested addition below:
> 
> I did that in the first series, but there are too many reasons to block
> in blk-mq [1]. I dropped blk-mq work in v2.
> 
> [1] https://patchwork.kernel.org/patch/9571051/

Well, that's not really good. If we cannot support this for both blk-mq and
legacy block layer the feature will not be usable. So please work on blk-mq
support as well.

								Honza 

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR