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Re: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in blk_bio_segment_split()

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On Wed, May 03, 2017 at 08:54:55AM +1000, NeilBrown wrote:
> On Tue, May 02 2017, Ming Lei wrote:
> 
> > On Tue, May 02, 2017 at 01:42:26PM +1000, NeilBrown wrote:
> >> blk_bio_segment_split() makes sure bios have no more than
> >> BIO_MAX_PAGES entries in the bi_io_vec.
> >> This was done because bio_clone_bioset() (when given a
> >> mempool bioset) could not handle larger io_vecs.
> >> 
> >> No driver uses bio_clone_bioset() any more, they all
> >> use bio_clone_fast() if anything, and bio_clone_fast()
> >> doesn't clone the bi_io_vec.
> >
> > Maybe in future, some drivers still may try to use 
> > bio_clone_bioset() again, I suggest to add some comments
> > on bio_clone_bioset() to make this usage explicitly. Also
> > better to trigger a warning if a big src bio is passed to
> > bio_clone_bioset().
> 
> There are now just two users for bio_clone_bioset(): bounce.c and btrfs.
> 
> Christoph wants to get rid of bounce.c, which would leave one.
> 
> I'd have to drill into the btrfs code to be sure, but it might be that
> btrfs only needs bio_clone_fast().  That would leave zero users.
> Then we wouldn't need a warning at all.
> 
> So I agree that we need to guard against future incorrect usage.  I'm not
> yet sure what the best approach is.

I think it is helpful to simply comment this function as obsolete.


Thanks,
Ming

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[PATCH 00/13] block: assorted cleanup for bio splitting and cloning. NeilBrown <neilb@suse.com> - 2017-05-02 05:50 +0200
  [PATCH 04/13] blk: use non-rescuing bioset for q->bio_split. NeilBrown <neilb@suse.com> - 2017-05-02 05:50 +0200
    Re: [PATCH 04/13] blk: use non-rescuing bioset for q->bio_split. Ming Lei <ming.lei@redhat.com> - 2017-05-02 14:00 +0200
    [PATCH 04/13 V2] blk: use non-rescuing bioset for q->bio_split. NeilBrown <neilb@suse.com> - 2017-05-03 01:30 +0200
  [PATCH 06/13] rbd: use bio_clone_fast() instead of bio_clone() NeilBrown <neilb@suse.com> - 2017-05-02 05:50 +0200
  [PATCH 10/13] xen-blkfront: remove bio splitting. NeilBrown <neilb@suse.com> - 2017-05-02 05:50 +0200
    Re: [PATCH 10/13] xen-blkfront: remove bio splitting. Christoph Hellwig <hch@infradead.org> - 2017-05-02 10:20 +0200
  [PATCH 07/13] drbd: use bio_clone_fast() instead of bio_clone() NeilBrown <neilb@suse.com> - 2017-05-02 05:50 +0200
    [PATCH 07/13 V2] drbd: use bio_clone_fast() instead of bio_clone() NeilBrown <neilb@suse.com> - 2017-05-03 01:30 +0200
  [PATCH 13/13] block: don't check for BIO_MAX_PAGES in  blk_bio_segment_split() NeilBrown <neilb@suse.com> - 2017-05-02 05:50 +0200
    Re: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in  blk_bio_segment_split() Christoph Hellwig <hch@infradead.org> - 2017-05-02 10:20 +0200
    Re: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in  blk_bio_segment_split() Ming Lei <ming.lei@redhat.com> - 2017-05-02 12:30 +0200
      Re: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in blk_bio_segment_split() NeilBrown <neilb@suse.com> - 2017-05-03 01:00 +0200
        Re: [PATCH 13/13] block: don't check for BIO_MAX_PAGES in  blk_bio_segment_split() Ming Lei <ming.lei@redhat.com> - 2017-05-03 02:00 +0200
  [PATCH 12/13] block: remove bio_clone() and all references. NeilBrown <neilb@suse.com> - 2017-05-02 05:50 +0200
  Re: [PATCH 00/13] block: assorted cleanup for bio splitting and cloning. NeilBrown <neilb@suse.com> - 2017-05-11 03:00 +0200

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