From: Jens Axboe <axboe@kernel.dk>
To: Shaohua Li <shli@kernel.org>, linux-kernel@vger.kernel.org
Cc: hch@infradead.org, kmo@daterainc.com
Subject: Re: [patch 2/2]blk-mq: Don't reserve a tag for flush request
Date: Tue, 31 Dec 2013 09:12:33 -0700 [thread overview]
Message-ID: <52C2ECF1.3020808@kernel.dk> (raw)
In-Reply-To: <20131231033850.GB31994@kernel.org>
On 12/30/2013 08:38 PM, Shaohua Li wrote:
>
> Reserving a tag (request) for flush to avoid dead lock is a overkill. tag is
> valuable resource. We can track flush request number and disallow too many
> pending flush requests allocated. With this patch,
> blk_mq_alloc_request_pinned() could do a busy nop (but not a dead loop) if too
> pending requests are allocated and new flush request is allocating. But this
> should not be a problem, too many pending flush requests are very rare case.
>
> I verified this can fix the deadlock caused by too many pending flush requests.
I think this looks pretty good, and it's a lot better than the hack that
is currently in place. The atomic inc/dec should be a noop on a per-hctx
basis, especially when it's only per-flush...
I'll get this queued up, with the ida fix too.
--
Jens Axboe
prev parent reply other threads:[~2013-12-31 16:13 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-31 3:38 [patch 2/2]blk-mq: Don't reserve a tag for flush request Shaohua Li
2013-12-31 16:12 ` Jens Axboe [this message]
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