From: Bart Van Assche <bvanassche@acm.org>
To: Ming Lei <ming.lei@redhat.com>,
James Bottomley <James.Bottomley@HansenPartnership.com>,
linux-scsi@vger.kernel.org,
"Martin K . Petersen" <martin.petersen@oracle.com>
Cc: linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
"Ewan D . Milne" <emilne@redhat.com>,
Hannes Reinecke <hare@suse.com>
Subject: Re: [PATCH V4 2/3] scsi: core: avoid to pre-allocate big chunk for protection meta data
Date: Mon, 29 Apr 2019 11:15:52 -0700 [thread overview]
Message-ID: <1556561752.161891.165.camel@acm.org> (raw)
In-Reply-To: <20190428073932.9898-3-ming.lei@redhat.com>
On Sun, 2019-04-28 at 15:39 +0800, Ming Lei wrote:
> Now scsi_mq_setup_tags() pre-allocates a big buffer for protection
> sg entries, and the buffer size is scsi_mq_sgl_size().
>
> This way isn't correct, scsi_mq_sgl_size() is used to pre-allocate
> sg entries for IO data. And the protection data buffer is much less,
> for example, one 512byte sector needs 8byte protection data, and
> the max sector number for one request is 2560(BLK_DEF_MAX_SECTORS),
> so the max protection data size is just 20k.
>
> The usual case is that one bio builds one single bip segment. Attribute
> to bio split, bio merge is seldom done for big IO, and it is only done
> in case of small bios. And protection data segment number is usually
> same with bio count in the request, so the number won't be very big,
> and allocating from slab is fast enough.
>
> Reduce to pre-allocate one sg entry for protection data, and switch
> to runtime allocation in case that the protection data segment number
> is bigger than 1. Then we can save huge pre-alocation, for example,
> 500
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
next prev parent reply other threads:[~2019-04-29 18:15 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-28 7:39 [PATCH V4 0/3] scsi: core: avoid big pre-allocation for sg list Ming Lei
2019-04-28 7:39 ` [PATCH V4 1/3] lib/sg_pool.c: improve APIs for allocating sg pool Ming Lei
2019-04-28 12:04 ` Christoph Hellwig
2019-04-28 7:39 ` [PATCH V4 2/3] scsi: core: avoid to pre-allocate big chunk for protection meta data Ming Lei
2019-04-29 18:15 ` Bart Van Assche [this message]
2019-04-28 7:39 ` [PATCH V4 3/3] scsi: core: avoid to pre-allocate big chunk for sg list Ming Lei
2019-04-29 18:16 ` Bart Van Assche
2019-06-03 20:44 ` Guenter Roeck
2019-06-04 1:00 ` Ming Lei
2019-06-04 3:49 ` Guenter Roeck
2019-06-04 4:10 ` Ming Lei
2019-06-04 14:51 ` Guenter Roeck
2019-06-04 6:55 ` Ming Lei
2019-05-05 1:10 ` [PATCH V4 0/3] scsi: core: avoid big pre-allocation " Ming Lei
2019-05-14 2:06 ` Martin K. Petersen
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