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

Kirill Tkhai
2020-02-12T20:04:23Z

On 12.02.2020 21:31, Darrick J. Wong wrote:
> On Wed, Feb 12, 2020 at 08:33:52PM +0300, Kirill Tkhai wrote:
>> 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?
>
> I mostly meant that the indent for the nth lines ought to be more than a
> single indent to make it easier to scan through the code, but you're
> right, the kernel indentation style is uglier. I could suggest
> something like this, which actually does fit:
>
> case FALLOC_FL_KEEP_SIZE:
> error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
> GFP_KERNEL,
> BLKDEV_ZERO_ALLOCATE | BLKDEV_ZERO_NOFALLBACK);
> break;
>
> But that's apparently apocryphal. :/

Just to mention.

We could also introduce BLKDEV_ZERO_ALLOCATE_NOFALLBACK, which is combination
of both bits. But this does not look good for me, since this make grep over
kernel code more difficult. And it won't good to introduce a new identifier
for a single place.

> --D
>
>>>> 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