Re: [PATCH v6 4/6] block: Add support for REQ_ALLOCATE flag

Kirill Tkhai
2020-02-12T17:34:31Z

Hi, Darrick,

On 12.02.2020 19:58, Darrick J. Wong wrote:
> On Mon, Feb 10, 2020 at 12:33:53PM +0300, Kirill Tkhai wrote:
>> This adds support for REQ_ALLOCATE extension of REQ_OP_WRITE_ZEROES
>> operation, which encourages a block device driver to just allocate
>> blocks (or mark them allocated) instead of actual blocks zeroing.
>> REQ_ALLOCATE is aimed to be used for network filesystems providing
>> a block device interface. Also, block devices, which map a file
>> on other filesystem (like loop), may use this for less fragmentation
>> and batching fallocate() requests. Hypervisors like QEMU may
>> introduce optimizations of clusters allocations based on this.
>>
>> BLKDEV_ZERO_ALLOCATE is a new corresponding flag for
>> blkdev_issue_zeroout().
>>
>> Stacking devices start from zero max_allocate_sectors limit for now,
>> and the support is going to be implemented separate for each device
>> in the future.
>>
>> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
>> Reviewed-by: Bob Liu <bob.liu@oracle.com>
>> ---
>> block/blk-lib.c | 17 ++++++++++-------
>> block/blk-settings.c | 4 ++++
>> fs/block_dev.c | 4 ++++
>> include/linux/blk_types.h | 5 ++++-
>> include/linux/blkdev.h | 13 ++++++++++---
>> 5 files changed, 32 insertions(+), 11 deletions(-)
>>
>> diff --git a/block/blk-lib.c b/block/blk-lib.c
>> index 3e38c93cfc53..9cd6f86523ba 100644
>> --- a/block/blk-lib.c
>> +++ b/block/blk-lib.c
>> @@ -214,7 +214,7 @@ static int __blkdev_issue_write_zeroes(struct block_device *bdev,
>> struct bio **biop, unsigned flags)
>> {
>> struct bio *bio = *biop;
>> - unsigned int max_write_zeroes_sectors;
>> + unsigned int max_write_zeroes_sectors, req_flags = 0;
>> struct request_queue *q = bdev_get_queue(bdev);
>>
>> if (!q)
>> @@ -224,18 +224,21 @@ static int __blkdev_issue_write_zeroes(struct block_device *bdev,
>> return -EPERM;
>>
>> /* Ensure that max_write_zeroes_sectors doesn't overflow bi_size */
>> - max_write_zeroes_sectors = bdev_write_zeroes_sectors(bdev, 0);
>> + max_write_zeroes_sectors = bdev_write_zeroes_sectors(bdev, flags);
>>
>> if (max_write_zeroes_sectors == 0)
>> return -EOPNOTSUPP;
>>
>> + if (flags & BLKDEV_ZERO_NOUNMAP)
>> + req_flags |= REQ_NOUNMAP;
>> + if (flags & BLKDEV_ZERO_ALLOCATE)
>> + req_flags |= REQ_ALLOCATE|REQ_NOUNMAP;
>> +
>> while (nr_sects) {
>> bio = blk_next_bio(bio, 0, gfp_mask);
>> bio->bi_iter.bi_sector = sector;
>> bio_set_dev(bio, bdev);
>> - bio->bi_opf = REQ_OP_WRITE_ZEROES;
>> - if (flags & BLKDEV_ZERO_NOUNMAP)
>> - bio->bi_opf |= REQ_NOUNMAP;
>> + bio->bi_opf = REQ_OP_WRITE_ZEROES | req_flags;
>>
>> if (nr_sects > max_write_zeroes_sectors) {
>> bio->bi_iter.bi_size = max_write_zeroes_sectors << 9;
>> @@ -362,7 +365,7 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
>> sector_t bs_mask;
>> struct bio *bio;
>> struct blk_plug plug;
>> - bool try_write_zeroes = !!bdev_write_zeroes_sectors(bdev, 0);
>> + bool try_write_zeroes = !!bdev_write_zeroes_sectors(bdev, flags);
>>
>> bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
>> if ((sector | nr_sects) & bs_mask)
>> @@ -391,7 +394,7 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
>> try_write_zeroes = false;
>> goto retry;
>> }
>> - if (!bdev_write_zeroes_sectors(bdev, 0)) {
>> + if (!bdev_write_zeroes_sectors(bdev, flags)) {
>> /*
>> * Zeroing offload support was indicated, but the
>> * device reported ILLEGAL REQUEST (for some devices
>> diff --git a/block/blk-settings.c b/block/blk-settings.c
>> index c8eda2e7b91e..8d5df9d37239 100644
>> --- a/block/blk-settings.c
>> +++ b/block/blk-settings.c
>> @@ -48,6 +48,7 @@ void blk_set_default_limits(struct queue_limits *lim)
>> lim->chunk_sectors = 0;
>> lim->max_write_same_sectors = 0;
>> lim->max_write_zeroes_sectors = 0;
>> + lim->max_allocate_sectors = 0;
>> lim->max_discard_sectors = 0;
>> lim->max_hw_discard_sectors = 0;
>> lim->discard_granularity = 0;
>> @@ -83,6 +84,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
>> lim->max_dev_sectors = UINT_MAX;
>> lim->max_write_same_sectors = UINT_MAX;
>> lim->max_write_zeroes_sectors = UINT_MAX;
>> + lim->max_allocate_sectors = 0;
>> }
>> EXPORT_SYMBOL(blk_set_stacking_limits);
>>
>> @@ -506,6 +508,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
>> b->max_write_same_sectors);
>> t->max_write_zeroes_sectors = min(t->max_write_zeroes_sectors,
>> b->max_write_zeroes_sectors);
>> + t->max_allocate_sectors = min(t->max_allocate_sectors,
>> + b->max_allocate_sectors);
>> t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
>>
>> t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index 69bf2fb6f7cd..1ffef894b3bd 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -2122,6 +2122,10 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
>> error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
>> GFP_KERNEL, BLKDEV_ZERO_NOFALLBACK);
>> break;
>> + case FALLOC_FL_KEEP_SIZE:
>> + error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
>> + GFP_KERNEL, BLKDEV_ZERO_ALLOCATE | BLKDEV_ZERO_NOFALLBACK);
>
> I think this should be ^^^ indented to match the other calls.

The only idea I have about this is something like the below. But the below is over 90 char...

error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
GFP_KERNEL,
BLKDEV_ZERO_ALLOCATE | BLKDEV_ZERO_NOFALLBACK);

Could you please clarify what you mean?

>> + break;
>> case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE | FALLOC_FL_NO_HIDE_STALE:
>> error = blkdev_issue_discard(bdev, start >> 9, len >> 9,
>> GFP_KERNEL, 0);
>> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
>> index 70254ae11769..86accd2caa4e 100644
>> --- a/include/linux/blk_types.h
>> +++ b/include/linux/blk_types.h
>> @@ -335,7 +335,9 @@ enum req_flag_bits {
>>
>> /* command specific flags for REQ_OP_WRITE_ZEROES: */
>> __REQ_NOUNMAP, /* do not free blocks when zeroing */
>> -
>> + __REQ_ALLOCATE, /* only notify about allocated blocks,
>> + * and do not actually zero them
>
> "only notify"? Is someone getting a notification? Or are we simply
> "notifying" the device that it must ensure allocated blocks?
>
> If it's that last one, then perhaps this should be reworded:
>
> /*
> * Ensure the LBA range is backed by physical storage
> * without writing zeroes to the blocks.
> */

Sounds good.

>> + */
>> __REQ_HIPRI,
>>
>> /* for driver use */
>> @@ -362,6 +364,7 @@ enum req_flag_bits {
>> #define REQ_CGROUP_PUNT (1ULL << __REQ_CGROUP_PUNT)
>>
>> #define REQ_NOUNMAP (1ULL << __REQ_NOUNMAP)
>> +#define REQ_ALLOCATE (1ULL << __REQ_ALLOCATE)
>> #define REQ_HIPRI (1ULL << __REQ_HIPRI)
>>
>> #define REQ_DRV (1ULL << __REQ_DRV)
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index 55a714161684..40707f980a2e 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -336,6 +336,7 @@ struct queue_limits {
>> unsigned int max_hw_discard_sectors;
>> unsigned int max_write_same_sectors;
>> unsigned int max_write_zeroes_sectors;
>> + unsigned int max_allocate_sectors;
>> unsigned int discard_granularity;
>> unsigned int discard_alignment;
>>
>> @@ -990,6 +991,8 @@ static inline struct bio_vec req_bvec(struct request *rq)
>> static inline unsigned int blk_queue_get_max_write_zeroes_sectors(
>> struct request_queue *q, unsigned int op_flags)
>> {
>> + if (op_flags & REQ_ALLOCATE)
>> + return q->limits.max_allocate_sectors;
>> return q->limits.max_write_zeroes_sectors;
>> }
>>
>> @@ -1226,6 +1229,7 @@ extern int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>>
>> #define BLKDEV_ZERO_NOUNMAP (1 << 0) /* do not free blocks */
>> #define BLKDEV_ZERO_NOFALLBACK (1 << 1) /* don't write explicit zeroes */
>> +#define BLKDEV_ZERO_ALLOCATE (1 << 2) /* allocate range of blocks */
>>
>> extern int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
>> sector_t nr_sects, gfp_t gfp_mask, struct bio **biop,
>> @@ -1430,10 +1434,13 @@ static inline unsigned int bdev_write_zeroes_sectors(struct block_device *bdev,
>> {
>> struct request_queue *q = bdev_get_queue(bdev);
>>
>> - if (q)
>> - return q->limits.max_write_zeroes_sectors;
>> + if (!q)
>> + return 0;
>>
>> - return 0;
>> + if (flags & BLKDEV_ZERO_ALLOCATE)
>> + return q->limits.max_allocate_sectors;
>> + else
>> + return q->limits.max_write_zeroes_sectors;
>> }
>>
>> static inline enum blk_zoned_model bdev_zoned_model(struct block_device *bdev)
>>
>>

Thanks,
Kirill