Re: [PATCH 03/13] scsi: unify allocation of scsi command and sense buffer
- From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
- Date: Mon, 25 May 2009 03:50:08 -0400
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.
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