On 07.01.2020 06:24, Martin K. Petersen wrote:
>
> Kirill,
>
> Sorry, the holiday break got in the way.
>
>> But I also worry about NOFALLBACK case. There are possible block
>> devices, which support write zeroes, but they can't allocate blocks
>> (block allocation are just not appliable for them, say, these are all
>> ordinary hdd).
>
> 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).
>> But won't it be a good thing to return EOPNOTSUPP right from
>> __blkdev_issue_write_zeroes() in case of block device can't allocate
>> blocks (q->limits.write_zeroes_can_allocate in the patch below)? Here
>> is just a way to underline block devices, which support write zeroes,
>> but allocation of blocks is meant nothing for them (wasting of time).
>
> 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"?
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):
diff --git a/block/blk-core.c b/block/blk-core.c
index 50a5de025d5e..4c45417838f7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -978,7 +978,8 @@ 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 & REQ_NOZERO))
goto not_supported;
break;
default:
@@ -1250,10 +1251,10 @@ 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-merge.c b/block/blk-merge.c
index 347782a24a35..0cdf7d0386c8 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -105,15 +105,22 @@ 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;
+
+ if (bio->bi_opf & REQ_NOZERO)
+ max_sectors = q->limits.max_allocate_sectors;
+ else
+ max_sectors = q->limits.max_write_zeroes_sectors;
+
*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..3f68a60cb196 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -506,6 +506,8 @@ 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/include/linux/blkdev.h b/include/linux/blkdev.h
index 9e3cd3394dd6..6219604a0c12 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;
@@ -989,9 +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, bool allocate)
+{
+ if (allocate)
+ 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);
@@ -1000,7 +1010,8 @@ 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 & REQ_NOZERO);
return q->limits.max_sectors;
}
