linux-kernel - Re: [PATCH v4 06/11] md/raid5: get rid of bio_fits

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Date:	Wed, 27 May 2015 10:38:36 +1000
From:	NeilBrown <neilb@...e.de>
To:	Ming Lin <mlin@...nel.org>
Cc:	Christoph Hellwig <hch@....de>,
	lkml <linux-kernel@...r.kernel.org>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Jens Axboe <axboe@...nel.dk>, Dongsu Park <dpark@...teo.net>,
	linux-raid@...r.kernel.org
Subject: Re: [PATCH v4 06/11] md/raid5: get rid of bio_fits_rdev()

On Tue, 26 May 2015 16:42:35 -0700 Ming Lin <mlin@...nel.org> wrote:

> On Tue, May 26, 2015 at 4:03 PM, NeilBrown <neilb@...e.de> wrote:
> > On Tue, 26 May 2015 15:32:38 -0700 Ming Lin <mlin@...nel.org> wrote:
> >
> >> On Tue, May 26, 2015 at 7:33 AM, Ming Lin <mlin@...nel.org> wrote:
> >> > On Mon, May 25, 2015 at 7:17 AM, Christoph Hellwig <hch@....de> wrote:
> >> >> On Mon, May 25, 2015 at 05:54:14PM +1000, NeilBrown wrote:
> >> >>> Did I write that?  I guess I did :-(
> >> >>> I meant *after*.   Don't get rid of bio_fits_rdev until split_bio is in
> >> >>> chunk_aligned_read().
> >> >>
> >> >> I suspect the whole series could use some reordering.
> >> >
> >> > Nice reordering.
> >> > I'll do this.
> >>
> >> Here is the reordering.
> >> https://git.kernel.org/cgit/linux/kernel/git/mlin/linux.git/log/?h=block-generic-req
> >>
> >> I'll post it if you are OK.
> >>
> >> [PATCH 01/15] block: add blk_queue_split()
> >> [PATCH 02/15] md: remove ->merge_bvec_fn
> >> [PATCH 03/15] dm: remov merge functions
> >> [PATCH 04/15] drbd: remove ->merge_bvec_fn
> >> [PATCH 05/15] pktcdvd: remove ->merge_bvec_fn
> >> [PATCH 06/15] rbd: remove ->merge_bvec_fn
> >> [PATCH 07/15] bcache: remove driver private bio splitting code
> >> [PATCH 08/15] btrfs: remove bio splitting and merge_bvec_fn() calls
> >> [PATCH 09/15] block: call blk_queue_split() in make_request functions
> >> [PATCH 10/15] block: kill ->merge_bvec_fn and simplify bio_add_page
> >> [PATCH 11/15] block: remove split code in blkdev_issue_discard
> >> [PATCH 12/15] md/raid5: get rid of bio_fits_rdev()
> >> [PATCH 13/15] block: remove bio_get_nr_vecs()
> >> [PATCH 14/15] fs: use helper bio_add_page() instead of open coding on
> >> [PATCH 15/15] Documentation: update notes in biovecs about
> >
> > The changes to dm.c and dm.h should be in the "dm:" patch, not "md:".
> 
> Will move it.
> 
> >
> > But I don't think the sequence is right.
> >
> > You cannot remove ->merge_bvec_fn for *any* stacked device until *all* devices
> > make use of blk_queue_split() (or otherwise handle arbitrarily large bios).
> >
> > I think it would be easiest to:
> >  - add blk_queue_split() and call it from common code before ->make_request_fn
> >    is called.  The ensure all devices can accept arbitrarily large bios.
> 
> For "common code", do you mean "generic_make_request()"
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index fbbb337..bb6455b 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1942,6 +1942,7 @@ void generic_make_request(struct bio *bio)
>         do {
>                 struct request_queue *q = bdev_get_queue(bio->bi_bdev);
> 
> +               blk_queue_split(q, &bio, q->bio_split);
>                 q->make_request_fn(q, bio);
> 
>                 bio = bio_list_pop(current->bio_list);

Yes, that is what I mean (assuming that is the only place that calls
->make_request_fn).

Thanks,
NeilBrown



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