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md: add proper merge_bvec handling to RAID0 and Linear.
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These personalities currently set a max request size of one page
when any member device has a merge_bvec_fn because they don't
bother to call that function.

This causes extra works in splitting and combining requests.

So make the extra effort to call the merge_bvec_fn when it exists
so that we end up with larger requests out the bottom.

Signed-off-by: NeilBrown <neilb@suse.de>
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NeilBrown committed Mar 19, 2012
1 parent dafb20f commit ba13da4
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Showing 3 changed files with 107 additions and 88 deletions.
30 changes: 15 additions & 15 deletions drivers/md/linear.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -68,10 +68,19 @@ static int linear_mergeable_bvec(struct request_queue *q,
struct dev_info *dev0;
unsigned long maxsectors, bio_sectors = bvm->bi_size >> 9;
sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
int maxbytes = biovec->bv_len;
struct request_queue *subq;

rcu_read_lock();
dev0 = which_dev(mddev, sector);
maxsectors = dev0->end_sector - sector;
subq = bdev_get_queue(dev0->rdev->bdev);
if (subq->merge_bvec_fn) {
bvm->bi_bdev = dev0->rdev->bdev;
bvm->bi_sector -= dev0->end_sector - dev0->rdev->sectors;
maxbytes = min(maxbytes, subq->merge_bvec_fn(subq, bvm,
biovec));
}
rcu_read_unlock();

if (maxsectors < bio_sectors)
Expand All @@ -80,12 +89,12 @@ static int linear_mergeable_bvec(struct request_queue *q,
maxsectors -= bio_sectors;

if (maxsectors <= (PAGE_SIZE >> 9 ) && bio_sectors == 0)
return biovec->bv_len;
/* The bytes available at this offset could be really big,
* so we cap at 2^31 to avoid overflow */
if (maxsectors > (1 << (31-9)))
return 1<<31;
return maxsectors << 9;
return maxbytes;

if (maxsectors > (maxbytes >> 9))
return maxbytes;
else
return maxsectors << 9;
}

static int linear_congested(void *data, int bits)
Expand Down Expand Up @@ -158,15 +167,6 @@ static struct linear_conf *linear_conf(struct mddev *mddev, int raid_disks)

disk_stack_limits(mddev->gendisk, rdev->bdev,
rdev->data_offset << 9);
/* as we don't honour merge_bvec_fn, we must never risk
* violating it, so limit max_segments to 1 lying within
* a single page.
*/
if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
blk_queue_max_segments(mddev->queue, 1);
blk_queue_segment_boundary(mddev->queue,
PAGE_CACHE_SIZE - 1);
}

conf->array_sectors += rdev->sectors;
cnt++;
Expand Down
154 changes: 85 additions & 69 deletions drivers/md/raid0.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -188,16 +188,10 @@ static int create_strip_zones(struct mddev *mddev, struct r0conf **private_conf)

disk_stack_limits(mddev->gendisk, rdev1->bdev,
rdev1->data_offset << 9);
/* as we don't honour merge_bvec_fn, we must never risk
* violating it, so limit ->max_segments to 1, lying within
* a single page.
*/

if (rdev1->bdev->bd_disk->queue->merge_bvec_fn) {
blk_queue_max_segments(mddev->queue, 1);
blk_queue_segment_boundary(mddev->queue,
PAGE_CACHE_SIZE - 1);
}
if (rdev1->bdev->bd_disk->queue->merge_bvec_fn)
conf->has_merge_bvec = 1;

if (!smallest || (rdev1->sectors < smallest->sectors))
smallest = rdev1;
cnt++;
Expand Down Expand Up @@ -290,8 +284,64 @@ static int create_strip_zones(struct mddev *mddev, struct r0conf **private_conf)
return err;
}

/* Find the zone which holds a particular offset
* Update *sectorp to be an offset in that zone
*/
static struct strip_zone *find_zone(struct r0conf *conf,
sector_t *sectorp)
{
int i;
struct strip_zone *z = conf->strip_zone;
sector_t sector = *sectorp;

for (i = 0; i < conf->nr_strip_zones; i++)
if (sector < z[i].zone_end) {
if (i)
*sectorp = sector - z[i-1].zone_end;
return z + i;
}
BUG();
}

/*
* remaps the bio to the target device. we separate two flows.
* power 2 flow and a general flow for the sake of perfromance
*/
static struct md_rdev *map_sector(struct mddev *mddev, struct strip_zone *zone,
sector_t sector, sector_t *sector_offset)
{
unsigned int sect_in_chunk;
sector_t chunk;
struct r0conf *conf = mddev->private;
int raid_disks = conf->strip_zone[0].nb_dev;
unsigned int chunk_sects = mddev->chunk_sectors;

if (is_power_of_2(chunk_sects)) {
int chunksect_bits = ffz(~chunk_sects);
/* find the sector offset inside the chunk */
sect_in_chunk = sector & (chunk_sects - 1);
sector >>= chunksect_bits;
/* chunk in zone */
chunk = *sector_offset;
/* quotient is the chunk in real device*/
sector_div(chunk, zone->nb_dev << chunksect_bits);
} else{
sect_in_chunk = sector_div(sector, chunk_sects);
chunk = *sector_offset;
sector_div(chunk, chunk_sects * zone->nb_dev);
}
/*
* position the bio over the real device
* real sector = chunk in device + starting of zone
* + the position in the chunk
*/
*sector_offset = (chunk * chunk_sects) + sect_in_chunk;
return conf->devlist[(zone - conf->strip_zone)*raid_disks
+ sector_div(sector, zone->nb_dev)];
}

/**
* raid0_mergeable_bvec -- tell bio layer if a two requests can be merged
* raid0_mergeable_bvec -- tell bio layer if two requests can be merged
* @q: request queue
* @bvm: properties of new bio
* @biovec: the request that could be merged to it.
Expand All @@ -303,21 +353,43 @@ static int raid0_mergeable_bvec(struct request_queue *q,
struct bio_vec *biovec)
{
struct mddev *mddev = q->queuedata;
struct r0conf *conf = mddev->private;
sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
sector_t sector_offset = sector;
int max;
unsigned int chunk_sectors = mddev->chunk_sectors;
unsigned int bio_sectors = bvm->bi_size >> 9;
struct strip_zone *zone;
struct md_rdev *rdev;
struct request_queue *subq;

if (is_power_of_2(chunk_sectors))
max = (chunk_sectors - ((sector & (chunk_sectors-1))
+ bio_sectors)) << 9;
else
max = (chunk_sectors - (sector_div(sector, chunk_sectors)
+ bio_sectors)) << 9;
if (max < 0) max = 0; /* bio_add cannot handle a negative return */
if (max < 0)
max = 0; /* bio_add cannot handle a negative return */
if (max <= biovec->bv_len && bio_sectors == 0)
return biovec->bv_len;
else
if (max < biovec->bv_len)
/* too small already, no need to check further */
return max;
if (!conf->has_merge_bvec)
return max;

/* May need to check subordinate device */
sector = sector_offset;
zone = find_zone(mddev->private, &sector_offset);
rdev = map_sector(mddev, zone, sector, &sector_offset);
subq = bdev_get_queue(rdev->bdev);
if (subq->merge_bvec_fn) {
bvm->bi_bdev = rdev->bdev;
bvm->bi_sector = sector_offset + zone->dev_start +
rdev->data_offset;
return min(max, subq->merge_bvec_fn(subq, bvm, biovec));
} else
return max;
}

Expand Down Expand Up @@ -397,62 +469,6 @@ static int raid0_stop(struct mddev *mddev)
return 0;
}

/* Find the zone which holds a particular offset
* Update *sectorp to be an offset in that zone
*/
static struct strip_zone *find_zone(struct r0conf *conf,
sector_t *sectorp)
{
int i;
struct strip_zone *z = conf->strip_zone;
sector_t sector = *sectorp;

for (i = 0; i < conf->nr_strip_zones; i++)
if (sector < z[i].zone_end) {
if (i)
*sectorp = sector - z[i-1].zone_end;
return z + i;
}
BUG();
}

/*
* remaps the bio to the target device. we separate two flows.
* power 2 flow and a general flow for the sake of perfromance
*/
static struct md_rdev *map_sector(struct mddev *mddev, struct strip_zone *zone,
sector_t sector, sector_t *sector_offset)
{
unsigned int sect_in_chunk;
sector_t chunk;
struct r0conf *conf = mddev->private;
int raid_disks = conf->strip_zone[0].nb_dev;
unsigned int chunk_sects = mddev->chunk_sectors;

if (is_power_of_2(chunk_sects)) {
int chunksect_bits = ffz(~chunk_sects);
/* find the sector offset inside the chunk */
sect_in_chunk = sector & (chunk_sects - 1);
sector >>= chunksect_bits;
/* chunk in zone */
chunk = *sector_offset;
/* quotient is the chunk in real device*/
sector_div(chunk, zone->nb_dev << chunksect_bits);
} else{
sect_in_chunk = sector_div(sector, chunk_sects);
chunk = *sector_offset;
sector_div(chunk, chunk_sects * zone->nb_dev);
}
/*
* position the bio over the real device
* real sector = chunk in device + starting of zone
* + the position in the chunk
*/
*sector_offset = (chunk * chunk_sects) + sect_in_chunk;
return conf->devlist[(zone - conf->strip_zone)*raid_disks
+ sector_div(sector, zone->nb_dev)];
}

/*
* Is io distribute over 1 or more chunks ?
*/
Expand Down Expand Up @@ -505,7 +521,7 @@ static void raid0_make_request(struct mddev *mddev, struct bio *bio)
}

sector_offset = bio->bi_sector;
zone = find_zone(mddev->private, &sector_offset);
zone = find_zone(mddev->private, &sector_offset);
tmp_dev = map_sector(mddev, zone, bio->bi_sector,
&sector_offset);
bio->bi_bdev = tmp_dev->bdev;
Expand Down
11 changes: 7 additions & 4 deletions drivers/md/raid0.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,13 +4,16 @@
struct strip_zone {
sector_t zone_end; /* Start of the next zone (in sectors) */
sector_t dev_start; /* Zone offset in real dev (in sectors) */
int nb_dev; /* # of devices attached to the zone */
int nb_dev; /* # of devices attached to the zone */
};

struct r0conf {
struct strip_zone *strip_zone;
struct md_rdev **devlist; /* lists of rdevs, pointed to by strip_zone->dev */
int nr_strip_zones;
struct strip_zone *strip_zone;
struct md_rdev **devlist; /* lists of rdevs, pointed to
* by strip_zone->dev */
int nr_strip_zones;
int has_merge_bvec; /* at least one member has
* a merge_bvec_fn */
};

#endif

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