linux-kernel - Re: [PATCH 03/13] scsi: unify allocation of scsi command and sense buffer

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Message-ID: <20090525074647.GK11363@kernel.dk>
Date:	Mon, 25 May 2009 09:46:47 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	chris.mason@...cle.com, david@...morbit.com,
	akpm@...ux-foundation.org, jack@...e.cz,
	yanmin_zhang@...ux.intel.com, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 03/13] scsi: unify allocation of scsi command and sense
	buffer

On Mon, May 25 2009, Christoph Hellwig wrote:
> On Mon, May 25, 2009 at 09:30:48AM +0200, Jens Axboe wrote:
> > Fold the sense buffer into the command, thereby eliminating a slab
> > allocation and free per command.
> 
> Might help to send it to linux-scsi to get people to review and apply it
> :)

yeah, as I later posted, this wasn't meant to be sent out as part of
the writeback series :-)

> But that patch looks good to me, avoiding one allocation for each
> command and simplifying the code.  I try to remember why these were
> two slabs to start with but can't find any reason.
> 
> Btw, we might just want to declare the sense buffer directly as a sized
> array in the scsi command as there really doesn't seem to be a reason
> not to allocate it.

That is also a workable solution. I've been trying to cut down on the
number of allocations required per-IO, and there's definitely still some
low hanging fruit there. Some of it is already included, like the inline
io_vecs in the bio.

-- 
Jens Axboe

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