From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: bytes/CDB of SCSI pass thru grossly limited maybe Date: Sat, 28 Aug 2004 20:41:09 +0200 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20040828184104.GA8460@suse.de> References: <20040828143124.GB2518@suse.de> <1093715498.3682.4.camel@mulgrave> <20040828175547.GA8339@suse.de> <1093717255.3682.13.camel@mulgrave> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from ns.virtualhost.dk ([195.184.98.160]:40416 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S267507AbUH1SlB (ORCPT ); Sat, 28 Aug 2004 14:41:01 -0400 Content-Disposition: inline In-Reply-To: <1093717255.3682.13.camel@mulgrave> List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Alan Stern , Pat LaVarre , SCSI development list On Sat, Aug 28 2004, James Bottomley wrote: > On Sat, 2004-08-28 at 13:55, Jens Axboe wrote: > > Probably bio and SCSI should use a unified MAX_PAGES define, there's not > > much point in bio setting up a 256 page bio_io_vec slab and mempool, if > > noone can use it. > > Sure, ours is SCSI_MAX_PHYS_SEGMENTS ... by default, we just use > MAX_PHYS_SEGMENTS from the bio headers for this, which is 128, we could > set this to BIO_MAX_PAGES, sure. > > We allow values of 32,64,128 and 256 (the smaller ones were for tiny > systems with SCSI stacks), the largest one for SGI/Qlogic. > > However, I did ask the IBM spearker at OLS who was doing the elevator > analysis to retry with 256 instead of 128, and he reported no difference > within error, so I don't think there's much evidence that 256 actually > does anything useful (other than consume a bit of spare memory). Since SCSI doesn't build > 128 pages anyways, yes it doesn't make sense to maintain a BIO_MAX_PAGES of 256. Didn't the SCSI part used to be 256 pages as well, I'm pretty sure that's what I put in when the scsi_malloc() crud was dumped? bio has 1, 4, 16, 64, 128, 256 pools. 32 might make more sense, I seem to recall mpages using that. I'll see if I can sneak a BIO_MAX_PAGES reduction in, and spend that extra pool on 32 instead :) -- Jens Axboe