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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 3/3] scsi: core: avoid to pre-allocate big chunk for sg list
Date: Mon, 29 Apr 2019 11:16:38 -0700	[thread overview]
Message-ID: <1556561798.161891.166.camel@acm.org> (raw)
In-Reply-To: <20190428073932.9898-4-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 IO sg list,
> and the buffer size is scsi_mq_sgl_size() which depends on smaller
> value between shost->sg_tablesize and SG_CHUNK_SIZE.
> 
> Modern HBA's DMA is often capable of deadling with very big segment
> number, so scsi_mq_sgl_size() is often big. Suppose the max sg number
> of SG_CHUNK_SIZE is taken, scsi_mq_sgl_size() will be 4KB.
> 
> Then if one HBA has lots of queues, and each hw queue's depth is
> high, pre-allocation for sg list can consume huge memory.
> For example of lpfc, nr_hw_queues can be 70, each queue's depth
> can be 3781, so the pre-allocation for data sg list is 70*3781*2k
> =517MB for single HBA.
> 
> There is Red Hat internal report that scsi_debug based tests can't
> be run any more since legacy io path is killed because too big
> pre-allocation.
> 
> So switch to runtime allocation for sg list, meantime pre-allocate 2
> inline sg entries. This way has been applied to NVMe PCI for a while,
> so it should be fine for SCSI too. Also runtime sg entries allocation
> has verified and run always in the original legacy io path.
> 
> Not see performance effect in my big BS test on scsi_debug.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>



  reply	other threads:[~2019-04-29 18:16 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
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 [this message]
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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