Re: [PATCH 2/2] md: raid1/raid10: initialize bvec table via bio_add_page()

[Ming Lei <ming.lei@redhat.com>]

On Thu, Jul 13, 2017 at 01:09:28PM +1000, NeilBrown wrote:
> On Thu, Jul 13 2017, Ming Lei wrote:
> 
> > On Thu, Jul 13, 2017 at 10:01:33AM +1000, NeilBrown wrote:
> >> On Wed, Jul 12 2017, Ming Lei wrote:
> >> 
> >> > We will support multipage bvec soon, so initialize bvec
> >> > table using the standardy way instead of writing the
> >> > talbe directly. Otherwise it won't work any more once
> >> > multipage bvec is enabled.
> >> >
> >> > Acked-by: Guoqing Jiang <gqjiang@suse.com>
> >> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> >> > ---
> >> >  drivers/md/md.c     | 21 +++++++++++++++++++++
> >> >  drivers/md/md.h     |  3 +++
> >> >  drivers/md/raid1.c  | 16 ++--------------
> >> >  drivers/md/raid10.c |  4 ++--
> >> >  4 files changed, 28 insertions(+), 16 deletions(-)
> >> >
> >> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> >> > index 8cdca0296749..cc8dcd928dde 100644
> >> > --- a/drivers/md/md.c
> >> > +++ b/drivers/md/md.c
> >> > @@ -9130,6 +9130,27 @@ void md_reload_sb(struct mddev *mddev, int nr)
> >> >  }
> >> >  EXPORT_SYMBOL(md_reload_sb);
> >> >  
> >> > +/* generally called after bio_reset() for reseting bvec */
> >> > +void md_bio_reset_resync_pages(struct bio *bio, struct resync_pages *rp,
> >> > +			       int size)
> >> > +{
> >> > +	int idx = 0;
> >> > +
> >> > +	/* initialize bvec table again */
> >> > +	do {
> >> > +		struct page *page = resync_fetch_page(rp, idx);
> >> > +		int len = min_t(int, size, PAGE_SIZE);
> >> > +
> >> > +		/*
> >> > +		 * won't fail because the vec table is big
> >> > +		 * enough to hold all these pages
> >> > +		 */
> >> > +		bio_add_page(bio, page, len, 0);
> >> > +		size -= len;
> >> > +	} while (idx++ < RESYNC_PAGES && size > 0);
> >> > +}
> >> > +EXPORT_SYMBOL(md_bio_reset_resync_pages);
> >> 
> >> I really don't think this is a good idea.
> >> This code is specific to raid1/raid10.  It is not generic md code.  So
> >> it doesn't belong here.
> >
> > We already added 'struct resync_pages' in drivers/md/md.h, so I think
> > it is reasonable to add this function into drivers/md/md.c
> 
> Alternative perspective: it was unreasonable to add "resync_pages" to
> md.h.
> 
> >
> >> 
> >> If you want to remove code duplication, then work on moving all raid1
> >> functionality into raid10.c, then discard raid1.c
> >
> > This patch is for avoiding new code duplication, not for removing current
> > duplication.
> >
> >> 
> >> Or at the very least, have a separate "raid1-10.c" file for the common
> >> code.
> >
> > You suggested it last time, but looks too overkill to be taken. But if
> > someone wants to refactor raid1 and raid10, I think it can be a good start,
> > but still not belong to this patch.
> 
> You are trying to create common code for raid1 and raid10.  This does
> not belong in md.c.
> If you really want to have a single copy of common code, then it exactly
> is the role of this patch to create a place to put it.
> I'm not saying you should put all common code in raid1-10.c.   Just the
> function that you have identified.

I really don't want to waste time on this kind of thing, I can do
either one frankly.

Shaohua, could you share me which way you like to merge? I can do it in
either way.

-- 
Ming