Re: PATCH md [001:002]: raid0: fix chunk size to 4K*n granularity

[raz ben yehuda <raziebe@gmail.com>]

Neil Hello
following this email are 6 patches. I fixed the errors as required.

patch 1:
Because of the removal the device list from
the strips raid0 did not compile with MD_DEBUG flag on.

patch 2:
informative : print to the user raid0 zones

patch 3:
Add support to chunk size of 4K*n instead of 4K*2^n

patch 4:
md to support page size chunks in the case of raid 0

patch 5:
md to support 1K*n chunks only in the case of raid 0

patch 6:
fix mdadm to path 1K*n chunks only in the case of raid0.
Commit is stacked on top mdadm.c


On Fri, 2009-05-15 at 08:35 +1000, Neil Brown wrote:
> On Thursday May 14, raziebe@gmail.com wrote:
> >  move raid0 chunk size to 4K*n granularity. 
> >  motivation for this patch is to have a better access to raid550. if a raid 5 is 3M
> >  stripe (4-1),and you have two of these raids 5's, and on top of you have a raid0, 
> >  it is better to access raid550 with a 3MB buffers and not 1M ( no raid5 write penalty).
> 
> I don't think you can justify "no raid5 write penalty" but it could
> possibly reduce the raid5 write penalty.
> 
> >  Andre, Patch is applied on top of your last post. now it is your turn to merge :)
> >  md.c    |   24 ++++++++++-----
> >  raid0.c |  102 ++++++++++++++++++++++++++++++----------------------------------
> >  
> >  2 files changed, 65 insertions(+), 61 deletions(-) 
> > Signed-Off-by:raziebe@gmail.com
> > 
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index ed5727c..5eab782 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -440,12 +440,14 @@ static inline sector_t calc_dev_sboffset(struct block_device *bdev)
> >  	return MD_NEW_SIZE_SECTORS(num_sectors);
> >  }
> >  
> > +
> 
> Just a single blank line between functions please.
> 
> >  static sector_t calc_num_sectors(mdk_rdev_t *rdev, unsigned chunk_size)
> >  {
> >  	sector_t num_sectors = rdev->sb_start;
> > -
> > -	if (chunk_size)
> > -		num_sectors &= ~((sector_t)chunk_size/512 - 1);
> > +	if (chunk_size) {
> > +		int chunk_sects = chunk_size>>9;
> > +		num_sectors = (num_sectors/chunk_sects)*chunk_sects;
> > +	}
> 
> You need to use "sector_div" here.  On a 32 bit host with 64bit
> sector_t you cannot use normal division.
> sector_div takes a sector_t and an "unsigned long", divides the one by
> the other, stores the quotient in the sector_t and returns the
> remainder.
> 
> >  	return num_sectors;
> >  }
> >  
> > @@ -3512,7 +3514,7 @@ min_sync_store(mddev_t *mddev, const char *buf, size_t len)
> >  
> >  	/* Must be a multiple of chunk_size */
> >  	if (mddev->chunk_size) {
> > -		if (min & (sector_t)((mddev->chunk_size>>9)-1))
> > +		if (min % (sector_t)(mddev->chunk_size>>9))
> 
> sector_div again.
> 
> >  			return -EINVAL;
> >  	}
> >  	mddev->resync_min = min;
> > @@ -3549,7 +3551,7 @@ max_sync_store(mddev_t *mddev, const char *buf, size_t len)
> >  
> >  		/* Must be a multiple of chunk_size */
> >  		if (mddev->chunk_size) {
> > -			if (max & (sector_t)((mddev->chunk_size>>9)-1))
> > +			if (max % (sector_t)((mddev->chunk_size>>9)))
> 
> and again.
> 
> >  				return -EINVAL;
> >  		}
> >  		mddev->resync_max = max;
> > @@ -3993,11 +3995,19 @@ static int do_md_run(mddev_t * mddev)
> >  		/*
> >  		 * chunk-size has to be a power of 2
> >  		 */
> > -		if ( (1 << ffz(~chunk_size)) != chunk_size) {
> > +		if ((1 << ffz(~chunk_size)) != chunk_size &&
> > +			 mddev->level != 0) {
> >  			printk(KERN_ERR "chunk_size of %d not valid\n", chunk_size);
> >  			return -EINVAL;
> >  		}
> > -
> > +		/*
> > +		* raid0 chunk size has to divide by a page
> > +		*/
> > +		if (mddev->level == 0 && (chunk_size % 4096)) {
> > +			printk(KERN_ERR "chunk_size of %d not valid\n",
> > +				chunk_size);
> > +			return -EINVAL;
> > +		}
> 
> Why does the chunk size have to be a multiple of page size?
> If there is a reason, include it in the comment.
> And the size of a page is PAGE_SIZE, not 4096.  On some systems
> PAGE_SIZE is 65536.
> 
> 
> >  		/* devices must have minimum size of one chunk */
> >  		list_for_each_entry(rdev, &mddev->disks, same_set) {
> >  			if (test_bit(Faulty, &rdev->flags))
> > diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> > index 36b747a..9865316 100644
> > --- a/drivers/md/raid0.c
> > +++ b/drivers/md/raid0.c
> > @@ -53,7 +53,7 @@ static int raid0_congested(void *data, int bits)
> >  }
> >  
> >  
> > -static int create_strip_zones (mddev_t *mddev)
> > +static int raid0_create_strip_zones(mddev_t *mddev)
> 
> Why did you add the "raid0_".  There is no value in a prefix like that
> on static functions.  Removing the trailing space is good though!
> 
> >  {
> >  	int i, c, j;
> >  	sector_t current_start, curr_zone_start;
> > @@ -237,7 +237,7 @@ static int raid0_mergeable_bvec(struct request_queue *q,
> >  	unsigned int chunk_sectors = mddev->chunk_size >> 9;
> >  	unsigned int bio_sectors = bvm->bi_size >> 9;
> >  
> > -	max =  (chunk_sectors - ((sector & (chunk_sectors - 1)) + bio_sectors)) << 9;
> > +	max =  (chunk_sectors - ((sector % chunk_sectors) + bio_sectors)) << 9;
> 
> sector_div...  but you get the point, I'll stop mentioning it.
> 
> >  	if (max < 0) max = 0; /* bio_add cannot handle a negative return */
> >  	if (max <= biovec->bv_len && bio_sectors == 0)
> >  		return biovec->bv_len;
> > @@ -259,26 +259,37 @@ static sector_t raid0_size(mddev_t *mddev, sector_t sectors, int raid_disks)
> >  	return array_sectors;
> >  }
> >  
> > +static int raid0_is_power2_chunk(mddev_t *mddev)
> > +{
> > +	if ((1 << ffz(~mddev->chunk_size)) == mddev->chunk_size)
> > +		return 1;
> > +	return 0;
> > +}
> 
> include/linux/log2.h has is_power_of_2.  Use that.
> And just say
>   is_power_of_2(mddev->chunk_size)
> where it is needed.  No need for a separate function.
> 
> 
> > +
> > +
> >  static int raid0_run(mddev_t *mddev)
> >  {
> >  	int ret;
> > +	int segment_boundary =  (mddev->chunk_size>>1)-1;
> >  
> >  	if (mddev->chunk_size == 0) {
> >  		printk(KERN_ERR "md/raid0: non-zero chunk size required.\n");
> >  		return -EINVAL;
> >  	}
> > -	printk(KERN_INFO "%s: setting max_sectors to %d, segment boundary to %d\n",
> > -	       mdname(mddev),
> > -	       mddev->chunk_size >> 9,
> > -	       (mddev->chunk_size>>1)-1);
> >  	blk_queue_max_sectors(mddev->queue, mddev->chunk_size >> 9);
> > -	blk_queue_segment_boundary(mddev->queue, (mddev->chunk_size>>1) - 1);
> > +	if (!raid0_is_power2_chunk(mddev))
> > +		segment_boundary = ~(ffz(~mddev->chunk_size))>>1;
> > +	printk(KERN_INFO "%s: setting max_sectors to %d, segment boundary to %d\n",
> > +		mdname(mddev),
> > +		mddev->chunk_size >> 9,
> > +		segment_boundary);
> > +	blk_queue_segment_boundary(mddev->queue, segment_boundary);
> 
> Setting blk_queue_segment_boundary here seems wrong.  I know you
> didn't add that code, you just modified.  But I think it might be
> best to remove it first - in a separate patch.
> I've just asked Peter Chubb who added that code in the first place if
> he has any idea why it was there.
> 
> >  	mddev->queue->queue_lock = &mddev->queue->__queue_lock;
> >  
> >  	mddev->private = kmalloc(sizeof(raid0_conf_t), GFP_KERNEL);
> >  	if (!mddev->private)
> >  		return -ENOMEM;
> > -	ret = create_strip_zones(mddev);
> > +	ret = raid0_create_strip_zones(mddev);
> >  	if (ret < 0) {
> >  		kfree(mddev->private);
> >  		mddev->private = NULL;
> > @@ -322,31 +333,35 @@ static int raid0_stop (mddev_t *mddev)
> >  	return 0;
> >  }
> >  
> > -/* Find the zone which holds a particular offset */
> > -static struct strip_zone *find_zone(struct raid0_private_data *conf,
> > -		sector_t sector)
> > +static int raid0_position_bio(mddev_t *mddev, struct bio *bio, sector_t sector)
> 
> You've removed a comment, changed the name of the function that it
> described, but have not provided a new comment to describe the new
> function..
> 
> And no "raid0_" prefix please.  I know a lot of function do still have
> that prefix but I would like the number to decrease, not increase.  It
> is redundant.
> 
> 
> >  {
> > -	int i;
> > -
> > -	for (i = 0; i < conf->nr_strip_zones; i++) {
> > -		struct strip_zone *z = conf->strip_zone + i;
> > -
> > -		if (sector < z->zone_start + z->sectors)
> > -			return z;
> > -	}
> > -	BUG();
> > -	return NULL;
> > +	sector_t sect_in_chunk;
> > +	mdk_rdev_t *tmp_dev;
> > +	sector_t chunk_in_dev;
> > +	sector_t rsect;
> > +	sector_t x;
> > +	raid0_conf_t *conf = mddev_to_conf(mddev);
> > +	sector_t chunk_sects = mddev->chunk_size >> 9;
> > +	struct strip_zone *zone = &conf->strip_zone[0];
> > +
> > +	while (sector >= zone->zone_start + zone->sectors)
> > +		zone++;
> > +	sect_in_chunk = sector % chunk_sects;
> > +	x = (sector - zone->zone_start) / chunk_sects;
> > +	sector_div(x, zone->nb_dev);
> > +	chunk_in_dev = x;
> > +	x = sector / chunk_sects;
> > +	tmp_dev = zone->dev[sector_div(x, zone->nb_dev)];
> > +	rsect = (chunk_in_dev * chunk_sects) + zone->dev_start + sect_in_chunk;
> > +	bio->bi_bdev = tmp_dev->bdev;
> > +	bio->bi_sector = rsect + tmp_dev->data_offset;
> > +	return 0;
> >  }
> 
> I would really like it if we only did division if division were need,
> and just use shift when that is possible.
> e..g
>   if (is_power_of_two())
>       do the shift version
>   else
>       do the divide version.
> 
> 
> >  
> > -static int raid0_make_request (struct request_queue *q, struct bio *bio)
> > +static int raid0_make_request(struct request_queue *q, struct bio *bio)
> >  {
> >  	mddev_t *mddev = q->queuedata;
> > -	unsigned int sect_in_chunk, chunksect_bits, chunk_sects;
> > -	raid0_conf_t *conf = mddev_to_conf(mddev);
> > -	struct strip_zone *zone;
> > -	mdk_rdev_t *tmp_dev;
> > -	sector_t chunk;
> > -	sector_t sector, rsect;
> > +	unsigned int chunk_sects;
> >  	const int rw = bio_data_dir(bio);
> >  	int cpu;
> >  
> > @@ -362,10 +377,9 @@ static int raid0_make_request (struct request_queue *q, struct bio *bio)
> >  	part_stat_unlock();
> >  
> >  	chunk_sects = mddev->chunk_size >> 9;
> > -	chunksect_bits = ffz(~chunk_sects);
> > -	sector = bio->bi_sector;
> >  
> > -	if (unlikely(chunk_sects < (bio->bi_sector & (chunk_sects - 1)) + (bio->bi_size >> 9))) {
> > +	if (unlikely(chunk_sects < ((bio->bi_sector % chunk_sects)
> > +			+ (bio->bi_size >> 9)))) {
> 
> Please keep things lines up properly.  The contents of a bracketed
> expression should never be to the left of the opening bracket, unless
> the opening bracket is the last symbol on the line.
> So this should be:
> > +	if (unlikely(chunk_sects < ((bio->bi_sector % chunk_sects)
> > +			            + (bio->bi_size >> 9)))) {
> 
> >  		struct bio_pair *bp;
> >  		/* Sanity check -- queue functions should prevent this happening */
> >  		if (bio->bi_vcnt != 1 ||
> > @@ -374,7 +388,8 @@ static int raid0_make_request (struct request_queue *q, struct bio *bio)
> >  		/* This is a one page bio that upper layers
> >  		 * refuse to split for us, so we need to split it.
> >  		 */
> > -		bp = bio_split(bio, chunk_sects - (bio->bi_sector & (chunk_sects - 1)));
> > +		bp = bio_split(bio, chunk_sects -
> > +					(bio->bi_sector % chunk_sects));
> 
> and this should be
> > +		bp = bio_split(bio, chunk_sects -
> > +				    (bio->bi_sector % chunk_sects));
> 
> 
> >  		if (raid0_make_request(q, &bp->bio1))
> >  			generic_make_request(&bp->bio1);
> >  		if (raid0_make_request(q, &bp->bio2))
> > @@ -383,29 +398,8 @@ static int raid0_make_request (struct request_queue *q, struct bio *bio)
> >  		bio_pair_release(bp);
> >  		return 0;
> >  	}
> > -	zone = find_zone(conf, sector);
> > -	if (!zone)
> > +	if (!raid0_position_bio(mddev, bio, bio->bi_sector))
> >  		return 1;
> > -	sect_in_chunk = bio->bi_sector & (chunk_sects - 1);
> > -	{
> > -		sector_t x = (sector - zone->zone_start) >> chunksect_bits;
> > -
> > -		sector_div(x, zone->nb_dev);
> > -		chunk = x;
> > -
> > -		x = sector >> chunksect_bits;
> > -		tmp_dev = zone->dev[sector_div(x, zone->nb_dev)];
> > -	}
> > -	rsect = (chunk << chunksect_bits) + zone->dev_start + sect_in_chunk;
> > - 
> > -	bio->bi_bdev = tmp_dev->bdev;
> > -	bio->bi_sector = rsect + tmp_dev->data_offset;
> > -
> > -	/*
> > -	 * Let the main block layer submit the IO and resolve recursion:
> > -	 */
> > -	return 1;
> > -
> >  bad_map:
> >  	printk("raid0_make_request bug: can't convert block across chunks"
> >  		" or bigger than %dk %llu %d\n", chunk_sects / 2,
> > 
> 
> 
> Thanks.
> I haven't thoroughly read through 'position_bio' so I reserve the
> right to comment further on that :-)
> But apart from the various observations above, it looks like it is
> heading in the right direction.
> 
> NeilBrown