netdev - Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle facility?

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Date:	Thu, 7 Apr 2016 08:11:51 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Jesper Dangaard Brouer <brouer@...hat.com>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Tom Herbert <tom@...bertland.com>,
	Brenden Blanco <bblanco@...mgrid.com>,
	"lsf@...ts.linux-foundation.org" <lsf@...ts.linux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"lsf-pc@...ts.linux-foundation.org" 
	<lsf-pc@...ts.linux-foundation.org>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle facility?

On 04/07/16 07:38, Christoph Hellwig wrote:
> This is also very interesting for storage targets, which face the same
> issue.  SCST has a mode where it caches some fully constructed SGLs,
> which is probably very similar to what NICs want to do.

I think a cached allocator for page sets + the scatterlists that 
describe these page sets would not only be useful for SCSI target 
implementations but also for the Linux SCSI initiator. Today the scsi-mq 
code reserves space in each scsi_cmnd for a scatterlist of 
SCSI_MAX_SG_SEGMENTS. If scatterlists would be cached together with page 
sets less memory would be needed per scsi_cmnd. See also 
scsi_mq_setup_tags() and scsi_alloc_sgtable().

Bart.