On Tue, 26 May 2009 13:36:43 +0900 FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > On Mon, 25 May 2009 03:50:08 -0400 > Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > 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. > > We discussed this idea when I rewrote the sense allocation code, I > think. > > I like that idea that unifying scsi_cmnd and llds' per-commad > structure however there is one tricky thing about it. > > Currently, a lld frees (or reuses) its per-commad structure when it > calls scsi_done(). SCSI-ml uses scsi_cmd after that so we need to > change the lifetime management (so we need to inspect all the llds, > e.g. this change will break iscsi ldd). Oops, as you said, this can be optional (so we don't need to convert all llds). But as I said, this changes the definition of when scsi_cmnd is free and ldds don't like that change, I think. > With that change, we can't tell llds how many per-commad structure are > possibly necessary. In general, LLDs want to know the maximum number > of per-commad structure; drivers allocates the number of per-commad > structure equal to host_template->can_queue. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
