Re: [PATCH 0/5] convert sg to use the block layer

[Jens Axboe <jens.axboe@oracle.com>]

On Wed, Aug 27 2008, FUJITA Tomonori wrote:
> On Tue, 26 Aug 2008 09:56:28 +0200
> Jens Axboe <jens.axboe@oracle.com> wrote:
> 
> > On Tue, Aug 26 2008, FUJITA Tomonori wrote:
> > > This patchset converts sg to use the block layer functions. That is,
> > > sg doesn't use scsi_execute_async() any more. This is a part of the
> > > overdue task to remove scsi_req_map_sg.
> > > 
> > > I tested this patchset with sg v3 and the old interface (struct
> > > sg_header) via SG_IO (v3) and the vfs API.
> > > 
> > > 
> > > Doug,
> > > 
> > > 1. I don't demote the sg driver's GFP_ATOMIC to GFP_KERNEL. sg always
> > > uses GFP_ATOMIC as before.
> > > 
> > > 2. I don't remove GFP_DMA allocation. As before, sg allocates reserved
> > > pages with GFP_DMA (sfp->low_dma case).
> > > 
> > > 3. I keep the reserved buffer per struct sg_fd as before.
> > > 
> > > 4. I use high-order page allocation for reserved buffer as before. sg
> > > works well with HBAs that have the limitation of the number of sg
> > > entries.
> > > 
> > > 5. I think that you were concern about the overhead of the block layer
> > > functions. But if you look at scsi_execute_async() that sg uses now,
> > > you can find that scsi_execute_async() uses the block layer functions
> > > internally. So the current sg incurs the overhead (if such overhead
> > > exists).
> > > 
> > > 
> > > Jens,
> > > 
> > > I keep the block API changes to a minimum (I might need more changes
> > > for st/osst but I'd like to progress step by step). I did only two
> > > things.
> > > 
> > > 1. I add gfp_mask argument to blk_rq_map_user and blk_rq_map_user_iov.
> > > 
> > > 2. I introduces struct rq_map_data holding pages. sg puts
> > > pre-allocated pages to it and passes it to bio_copy_user_iov(). The
> > > current users of bio_copy_user_iov simply passes NULL. blk_rq_map_user
> > > and blk_rq_map_user_iov take a pointer to struct rq_map_data and in
> > > the end bio_copy_user_iov gets it.
> > > 
> > > 
> > > This patchset against the for-linus branch in Jens' tree + the two
> > > patches for 2.6.27:
> > > 
> > > http://marc.info/?l=linux-kernel&m=121964251911717&w=2
> > > http://marc.info/?l=linux-kernel&m=121964241911611&w=2
> > > 
> > > After Jens rebases the for-2.6.28 brach, I'll update this patchset
> > > too.
> > 
> > Thanks a lot for doing this work, it's been pending for a long time.
> > I've rebased for-2.6.28 on top of for-linus to ease this integration, so
> > if you could resend the patchset then I can add it.
> 
> Thanks, I put an updated version against the for-2.6.28 branch in your
> tree:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/tomo/linux-2.6-misc.git sg-block
> 
> 
> Can you wait for a little while before applying this to your
> for-2.6.28 branch? We need Doug's ACK on this.

Sure, just let me know...

> But I think that it's nice if you can send this to linux-next since
> testing this patchset on linux-next is good.

for-2.6.28 is already in linux-next, so once this gets applied it'll get
tested there as well. And in -mm.

-- 
Jens Axboe