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

From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: Sagi Grimberg <sagi@grimberg.me>, jack@suse.com
Cc: hch@infradead.org, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org, linux-btrfs@vger.kernel.org,
	linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
	Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: Re: [PATCH 5/8] nowait aio: return on congested block device
Date: Wed, 8 Mar 2017 09:00:09 -0600	[thread overview]
Message-ID: <44cc02b1-f7ac-cbc6-6f09-726ae8225358@suse.de> (raw)
In-Reply-To: <0d1ba678-69c0-16ce-6c3e-475cd8da203c@grimberg.me>

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