Re: [PATCH 4/5] md/raid10: improve raid10 discard request

[Christoph Hellwig <hch@infradead.org>]

On Wed, Feb 03, 2021 at 09:45:30PM +0800, Xiao Ni wrote:
> +static struct bio *raid10_split_bio(struct r10conf *conf,
> +			struct bio *bio, sector_t sectors, bool want_first)
> +{
> +	struct bio *split;
> +
> +	split = bio_split(bio, sectors,	GFP_NOIO, &conf->bio_split);
> +	bio_chain(split, bio);
> +	allow_barrier(conf);
> +	if (want_first) {
> +		submit_bio_noacct(bio);
> +		bio = split;
> +	} else
> +		submit_bio_noacct(split);
> +	wait_barrier(conf);
> +
> +	return bio;

I'm not sure this helper makes much sense given that the two different
cases could just be open coded into the two callers.

> +		/* raid10_remove_disk uses smp_mb to make sure rdev is set to
> +		 * replacement before setting replacement to NULL. It can read
> +		 * rdev first without barrier protect even replacment is NULL
> +		 */

Not the normal kernel comment style.

> +/* There are some limitations to handle discard bio
> + * 1st, the discard size is bigger than stripe_size*2.
> + * 2st, if the discard bio spans reshape progress, we use the old way to
> + * handle discard bio
> + */

Same here.

> +static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
> +{
> +	struct r10conf *conf = mddev->private;
> +	struct geom *geo = &conf->geo;
> +	struct r10bio *r10_bio;
> +
> +	int disk;
> +	sector_t chunk;
> +	unsigned int stripe_size;
> +	unsigned int stripe_data_disks;
> +	sector_t split_size;
> +
> +	sector_t bio_start, bio_end;

Empty lines between variabe declarations also are kinda strange.

> +	stripe_data_disks = geo->near_copies ?
> +				geo->raid_disks / geo->near_copies +
> +				geo->raid_disks % geo->near_copies :
> +				geo->raid_disks;

Normal style would be an if/else here.

> +
> +	bio_start = bio->bi_iter.bi_sector;
> +	bio_end = bio_end_sector(bio);
> +
> +	/* Maybe one discard bio is smaller than strip size or across one stripe
> +	 * and discard region is larger than one stripe size. For far offset layout,

While there are occasional exceptions to the 80 char line rule, a block
comment should never qualify.

> +	 * if the discard region is not aligned with stripe size, there is hole
> +	 * when we submit discard bio to member disk. For simplicity, we only
> +	 * handle discard bio which discard region is bigger than stripe_size*2
> +	 */
> +	if (bio_sectors(bio) < stripe_size*2)

missing whitespaces around the *.