From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
linux-block@vger.kernel.org, Yu Kuai <yukuai3@huawei.com>
Subject: Re: [PATCH 3/3] blk-mq: don't clear flush_rq from tags->rqs[]
Date: Wed, 15 Jun 2022 08:22:41 +0200 [thread overview]
Message-ID: <20220615062241.GF22115@lst.de> (raw)
In-Reply-To: <20220615023712.750122-4-ming.lei@redhat.com>
On Wed, Jun 15, 2022 at 10:37:12AM +0800, Ming Lei wrote:
> commit 364b61818f65 ("blk-mq: clearing flush request reference in
> tags->rqs[]") is added to clear the to-be-free flush request from
> tags->rqs[] for avoiding use-after-free on the flush rq.
>
> Yu Kuai reported that blk_mq_clear_flush_rq_mapping() slows down boot time
> by ~8s because running scsi probe which may create and remove lots of
> unpresent LUNs on megaraid-sas which uses BLK_MQ_F_TAG_HCTX_SHARED and
> each request queue has lots of hw queues.
>
> Improve the situation by not running blk_mq_clear_flush_rq_mapping if
> disk isn't added when there can't be any flush request issued.
This looks ok. Another optimization would be to never do this if we
don't have a write cache enabled and thus never ever use the flush_rq.
Reviewed-by: Christoph Hellwig <hch@lst.de>
prev parent reply other threads:[~2022-06-15 6:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-15 2:37 [PATCH 0/3] blk-mq: three misc patches Ming Lei
2022-06-15 2:37 ` [PATCH 1/3] blk-mq: protect q->elevator by ->sysfs_lock Ming Lei
2022-06-15 6:01 ` Christoph Hellwig
2022-06-15 2:37 ` [PATCH 2/3] blk-mq: avoid to touch q->elevator without any protection Ming Lei
2022-06-15 6:04 ` Christoph Hellwig
2022-06-15 2:37 ` [PATCH 3/3] blk-mq: don't clear flush_rq from tags->rqs[] Ming Lei
2022-06-15 6:22 ` Christoph Hellwig [this message]
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