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

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Date:   Wed, 8 Mar 2017 09:00:09 -0600
From:   Goldwyn Rodrigues <rgoldwyn@...e.de>
To:     Sagi Grimberg <sagi@...mberg.me>, jack@...e.com
Cc:     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 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/

-- 
Goldwyn