Re: [PATCH RFC 1/3] block: Add support for REQ_OP_ASSIGN_RANGE operation

From: Kirill Tkhai
Date: Thu Jan 09 2020 - 04:45:05 EST

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On 08.01.2020 05:49, Martin K. Petersen wrote:
>
> Kirill,
>
>>> Correct. We shouldn't go down this path unless a device is thinly
>>> provisioned (i.e. max_discard_sectors > 0).
>>
>> (I assumed it is a typo, and you mean max_allocate_sectors like bellow).
>
> No, this was in the context of not having an explicit queue limit for
> allocation. If a device does not have max_discard_sectors > 0 then it is
> not thinly provisioned and therefore attempting allocation makes no
> sense.
>
>>> I don't like "write_zeroes_can_allocate" because that makes assumptions
>>> about WRITE ZEROES being the command of choice. I suggest we call it
>>> "max_allocate_sectors" to mirror "max_discard_sectors". I.e. put
>>> emphasis on the semantic operation and not the plumbing.
>>
>> Hm. Do you mean "bool max_allocate_sectors" or "unsigned int max_allocate_sectors"?
>
> unsigned int. At least for SCSI we could have a device which would use
> UNMAP for discards and WRITE SAME for allocates. And therefore the range
> limit could be different for the two operations. Sadly.
>
> I have a patch in the pipeline which deals with some problems in this
> department because some devices have a split brain wrt. their discard
> limits.
>
>> In the second case we should make all the
>> q->limits.max_write_zeroes_sectors dereferencing as switches like the
>> below (this is a partial patch and only several of places are
>> converted to switches as examples):
>
> Something like that, yes.
>
> This is getting a bit messy :( However, I am not sure that scattering
> REQ_OP_ALLOCATE all over the I/O stack is particularly attractive
> either.

It looks like changing the second argument of blk_queue_get_max_write_zeroes_sectors()
gives almost clean code. All REQ_NOZERO checks become moved to helper.

> Both REQ_OP_DISCARD and REQ_OP_WRITE_SAME come with some storage
> protocol baggage that forces us to have special handling all over the
> stack. But REQ_OP_WRITE_ZEROES is fairly clean and simple and, except
> for the potentially different block count limit, an allocate operation
> would be a carbon copy of the plumbing for write zeroes. A lot of
> duplication.
>
> So even through I'm increasingly torn on whether introducing separate
> REQ_OP_ALLOCATE plumbing throughout the stack or having a REQ_ALLOCATE
> flag for REQ_OP_WRITE_ZEROES is best, I still think I'm leaning towards
> the latter. That will also make it easier for me in the SCSI disk
> driver.

Yeah, this sounds good. Also, it looks the REQ_NOZERO patch is really
simpler, it is smaller even.

Below is complete patch for block core (I've excluded hunks for drivers/*,
since they require some cleanup patches for preparations). Please, let
me know whether I understood you correct and everything is OK. Thanks!

[PATCH] block: Add support for REQ_NOZERO

This adds support for REQ_NOZERO 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_NOZERO 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().

Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
---
block/blk-core.c | 6 +++---
block/blk-lib.c | 17 ++++++++++-------
block/blk-merge.c | 9 ++++++---
block/blk-settings.c | 4 ++++
fs/block_dev.c | 4 ++++
include/linux/blk_types.h | 5 ++++-
include/linux/blkdev.h | 32 ++++++++++++++++++++++++--------
7 files changed, 55 insertions(+), 22 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 50a5de025d5e..2edcd55624f1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -978,7 +978,7 @@ generic_make_request_checks(struct bio *bio)
goto not_supported;
break;
case REQ_OP_WRITE_ZEROES:
- if (!q->limits.max_write_zeroes_sectors)
+ if (!blk_queue_get_max_write_zeroes_sectors(q, bio->bi_opf))
goto not_supported;
break;
default:
@@ -1250,10 +1250,10 @@ EXPORT_SYMBOL(submit_bio);
static int blk_cloned_rq_check_limits(struct request_queue *q,
struct request *rq)
{
- if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, req_op(rq))) {
+ if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, rq->cmd_flags)) {
printk(KERN_ERR "%s: over max size limit. (%u > %u)\n",
__func__, blk_rq_sectors(rq),
- blk_queue_get_max_sectors(q, req_op(rq)));
+ blk_queue_get_max_sectors(q, rq->cmd_flags));
return -EIO;
}

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 5f2c429d4378..3e80279eb029 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);
+ 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_NOZERO|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);
+ 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)) {
+ 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-merge.c b/block/blk-merge.c
index 347782a24a35..e3ce4b87bbaa 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -105,15 +105,18 @@ static struct bio *blk_bio_discard_split(struct request_queue *q,
static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
struct bio *bio, struct bio_set *bs, unsigned *nsegs)
{
+ unsigned int max_sectors;
+
+ max_sectors = blk_queue_get_max_write_zeroes_sectors(q, bio->bi_opf);
*nsegs = 0;

- if (!q->limits.max_write_zeroes_sectors)
+ if (!max_sectors)
return NULL;

- if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
+ if (bio_sectors(bio) <= max_sectors)
return NULL;

- return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
+ return bio_split(bio, max_sectors, GFP_NOIO, bs);
}

static struct bio *blk_bio_write_same_split(struct request_queue *q,
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 5f6dcc7a47bd..09a2eeacfadd 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 = UINT_MAX;
}
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);
+ 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..9ed166860099 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_NOZERO, /* only notify about allocated blocks,
+ * and do not actual zero them
+ */
__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_NOZERO (1ULL << __REQ_NOZERO)
#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 c45779f00cbd..7e388be625af 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;

@@ -988,9 +989,19 @@ static inline struct bio_vec req_bvec(struct request *rq)
return mp_bvec_iter_bvec(rq->bio->bi_io_vec, rq->bio->bi_iter);
}

+static inline unsigned int blk_queue_get_max_write_zeroes_sectors(
+ struct request_queue *q, unsigned int op_flags)
+{
+ if (op_flags & REQ_NOZERO)
+ return q->limits.max_allocate_sectors;
+ return q->limits.max_write_zeroes_sectors;
+}
+
static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
- int op)
+ unsigned int op_flags)
{
+ int op = op_flags & REQ_OP_MASK;
+
if (unlikely(op == REQ_OP_DISCARD || op == REQ_OP_SECURE_ERASE))
return min(q->limits.max_discard_sectors,
UINT_MAX >> SECTOR_SHIFT);
@@ -999,7 +1010,7 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
return q->limits.max_write_same_sectors;

if (unlikely(op == REQ_OP_WRITE_ZEROES))
- return q->limits.max_write_zeroes_sectors;
+ return blk_queue_get_max_write_zeroes_sectors(q, op_flags);

return q->limits.max_sectors;
}
@@ -1029,10 +1040,10 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
if (!q->limits.chunk_sectors ||
req_op(rq) == REQ_OP_DISCARD ||
req_op(rq) == REQ_OP_SECURE_ERASE)
- return blk_queue_get_max_sectors(q, req_op(rq));
+ return blk_queue_get_max_sectors(q, rq->cmd_flags);

return min(blk_max_size_offset(q, offset),
- blk_queue_get_max_sectors(q, req_op(rq)));
+ blk_queue_get_max_sectors(q, rq->cmd_flags));
}

static inline unsigned int blk_rq_count_bios(struct request *rq)
@@ -1219,6 +1230,7 @@ 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,
@@ -1418,14 +1430,18 @@ static inline unsigned int bdev_write_same(struct block_device *bdev)
return 0;
}

-static inline unsigned int bdev_write_zeroes_sectors(struct block_device *bdev)
+static inline unsigned int bdev_write_zeroes_sectors(struct block_device *bdev,
+ unsigned int flags)
{
struct request_queue *q = bdev_get_queue(bdev);

- if (q)
+ if (!q)
+ return 0;
+
+ if (flags & BLKDEV_ZERO_ALLOCATE)
+ return q->limits.max_allocate_sectors;
+ else
return q->limits.max_write_zeroes_sectors;
-
- return 0;
}

static inline enum blk_zoned_model bdev_zoned_model(struct block_device *bdev)

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