From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 03/13] scsi: unify allocation of scsi command and sense buffer Date: Mon, 25 May 2009 03:50:08 -0400 Message-ID: <20090525075008.GA23413@infradead.org> References: <1243236668-3398-1-git-send-email-jens.axboe@oracle.com> <1243236668-3398-6-git-send-email-jens.axboe@oracle.com> <20090525074124.GA31746@infradead.org> <20090525074647.GK11363@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, chris.mason@oracle.com, david@fromorbit.com, akpm@linux-foundation.org, jack@suse.cz, yanmin_zhang@linux.intel.com, linux-scsi@vger.kernel.org To: Jens Axboe Return-path: Content-Disposition: inline In-Reply-To: <20090525074647.GK11363@kernel.dk> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Mon, May 25, 2009 at 09:46:47AM +0200, Jens Axboe wrote: > > 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. Btw, one thing I wanted to do for years is to add ->alloc_cmnd and ->destroy_cmnd method to the host template which optionally move the command allocation to the LLDD. That way we can embedd the scsi_cmnd into the drivers per-commad structure and eliminate another memory allocation. Also this would naturally extend the keep one cmnd pool to drivers without requiring additional code. As a second step it would also allow killing the scsi_host_cmd_pool byt just having a set of library routines that drivers which need SLAB_CACHE_DMA can use.