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

[Kirill Tkhai <ktkhai@virtuozzo.com>]

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