bcache: Set the logical block size to a sensible value
PATCH 1/1 bcache: Set the logical block size to a sensible value
Preserve the backing device's logical size, use 512 byte sectors when there is no backing device.
The logical block size has no impact on performance, but it alters the meaning of on-disk structures like partition tables. Preserve the backing device's sector size to keep bcache transparent, and use 512 byte sectors like everyone else when no backing device is present.
--- drivers/md/bcache/super.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
drivers/md/bcache/super.c +5 -4
@@ -745,11 +745,12 @@ static void bcache_device_free(struct bcache_device *d) bioset_free(d->bio_split); closure_debug_destroy(&d->cl); } -static int bcache_device_init(struct bcache_device *d, unsigned block_size) +static int bcache_device_init(struct bcache_device *d, unsigned block_size, + unsigned logical_size) { struct request_queue *q; if (!(d->bio_split = bioset_create(4, offsetof(struct bbio, bio))) || !(d->unaligned_bvec = mempool_create_kmalloc_pool(1,
@@ -774,11 +775,11 @@ static int bcache_device_init(struct bcache_device *d, unsigned block_size) q->limits.max_sectors =UINT_MAX ; q->limits.max_segment_size =UINT_MAX ; q->limits.max_segments =BIO_MAX_PAGES ; q->limits.max_discard_sectors =UINT_MAX ; q->limits.io_min = block_size; - q->limits.logical_block_size = block_size; + q->limits.logical_block_size = logical_size; q->limits.physical_block_size = block_size;set_bit (QUEUE_FLAG_NONROT , &d->disk->queue->queue_flags);set_bit (QUEUE_FLAG_DISCARD , &d->disk->queue->queue_flags);return 0 ;
@@ -1064,11 +1065,11 @@ static int cached_dev_init(struct cached_dev *dc, unsigned block_size)for (io = dc->io; io < dc->io +RECENT_IO ; io++) {list_add (&io->lru, &dc->io_lru);hlist_add_head (&io->hash, dc->io_hash +RECENT_IO ); } - ret =bcache_device_init (&dc->disk, block_size); + ret =bcache_device_init (&dc->disk, block_size, q->limits.logical_block_size);if (ret)return ret;set_capacity (dc->disk.disk, dc->bdev->bd_part->nr_sects - dc->sb.data_offset);
@@ -1163,11 +1164,11 @@ static int flash_dev_run(struct cache_set *c, struct uuid_entry *u)closure_init (&d->cl,NULL );set_closure_fn (&d->cl, flash_dev_flush, system_wq);kobject_init (&d->kobj, &bch_flash_dev_ktype); -if (bcache_device_init (d,block_bytes (c))) +if (bcache_device_init (d,block_bytes (c),512 )) goto err;bcache_device_attach (d, c, u - c->uuids);set_capacity (d->disk, u->sectors);bch_flash_dev_request_init (d);
Signature · 1 line
1.8.3.222.g430da9e
Quoted 8 lines · Gabriel de Perthuis
Preserve the backing device's logical size, use 512 byte sectors when there is no backing device.
The logical block size has no impact on performance, but it alters the meaning of on-disk structures like partition tables. Preserve the backing device's sector size to keep bcache transparent, and use 512 byte sectors like everyone else when no backing device is present.
To recap the IRC discussion for the list - we can't take this patch currently.
For those less familiar with these bits, the logical block size (per the sysfs docs) is the smallest IO size the device is capable of doing - physical_block_size can be bigger, for devices that do rmw internally.
Anyways, the problem is we currently can't expose a bcache device (cached volume or flash only volume) with a smaller block size than the cache device. This is fixable - and I'll probably have to do it eventually for other reasons - but it'll take some new not quite trivial code.
And there are SSDs (some of the niche pcie stuff) that don't support < 4k IOs, so we do have to make sure we expose the right blocksize. And since a bcache device can be brought up in passthrough mode and have a cache attached at runtime - this is why we get the blocksize from the backing device's superblock, instead of just using the logical block size of the backing device.
Quoted 66 lines
Signed-off-by Gabriel de Perthuis <[email protected]>--- drivers/md/bcache/super.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)drivers/md/bcache/super.c +5
-4@@ -745,11 +745,12 @@ static void bcache_device_free(struct bcache_device *d) bioset_free(d->bio_split); closure_debug_destroy(&d->cl); } -static int bcache_device_init(struct bcache_device *d, unsigned block_size) +static int bcache_device_init(struct bcache_device *d, unsigned block_size, + unsigned logical_size) { struct request_queue *q; if (!(d->bio_split = bioset_create(4, offsetof(struct bbio, bio))) || !(d->unaligned_bvec = mempool_create_kmalloc_pool(1,@@ -774,11 +775,11 @@ static int bcache_device_init(struct bcache_device *d, unsigned block_size) q->limits.max_sectors =UINT_MAX ; q->limits.max_segment_size =UINT_MAX ; q->limits.max_segments =BIO_MAX_PAGES ; q->limits.max_discard_sectors =UINT_MAX ; q->limits.io_min = block_size; - q->limits.logical_block_size = block_size; + q->limits.logical_block_size = logical_size; q->limits.physical_block_size = block_size;set_bit (QUEUE_FLAG_NONROT , &d->disk->queue->queue_flags);set_bit (QUEUE_FLAG_DISCARD , &d->disk->queue->queue_flags);return 0 ;@@ -1064,11 +1065,11 @@ static int cached_dev_init(struct cached_dev *dc, unsigned block_size)for (io = dc->io; io < dc->io +RECENT_IO ; io++) {list_add (&io->lru, &dc->io_lru);hlist_add_head (&io->hash, dc->io_hash +RECENT_IO ); } - ret =bcache_device_init (&dc->disk, block_size); + ret =bcache_device_init (&dc->disk, block_size, q->limits.logical_block_size);if (ret)return ret;set_capacity (dc->disk.disk, dc->bdev->bd_part->nr_sects - dc->sb.data_offset);@@ -1163,11 +1164,11 @@ static int flash_dev_run(struct cache_set *c, struct uuid_entry *u)closure_init (&d->cl,NULL );set_closure_fn (&d->cl, flash_dev_flush, system_wq);kobject_init (&d->kobj, &bch_flash_dev_ktype); -if (bcache_device_init (d,block_bytes (c))) +if (bcache_device_init (d,block_bytes (c),512 )) goto err;bcache_device_attach (d, c, u - c->uuids);set_capacity (d->disk, u->sectors);bch_flash_dev_request_init (d);Signature · 1 line
1.8.3.222.g430da9e