Commit 0034af03 authored by Jens Axboe's avatar Jens Axboe
Browse files

block: make /sys/block/<dev>/queue/discard_max_bytes writeable 



Lots of devices support huge discard sizes these days. Depending
on how the device handles them internally, huge discards can
introduce massive latencies (hundreds of msec) on the device side.

We have a sysfs file, discard_max_bytes, that advertises the max
hardware supported discard size. Make this writeable, and split
the settings into a soft and hard limit. This can be set from
'discard_granularity' and up to the hardware limit.

Add a new sysfs file, 'discard_max_hw_bytes', that shows the hw
set limit.

Reviewed-by: default avatarJeff Moyer <jmoyer@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 2bb4cd5c

Documentation/block/queue-sysfs.txt

+9 −1
Original line number Diff line number Diff line
@@ -20,7 +20,7 @@ This shows the size of internal allocation of the device in bytes, if 
reported by the device. A value of '0' means device does not support

the discard functionality.



discard_max_bytes (RO)

discard_max_hw_bytes (RO)

----------------------

Devices that support discard functionality may have internal limits on

the number of bytes that can be trimmed or unmapped in a single operation.
@@ -29,6 +29,14 @@ number of bytes that can be discarded in a single operation. Discard 
requests issued to the device must not exceed this limit. A discard_max_bytes

value of 0 means that the device does not support discard functionality.



discard_max_bytes (RW)

----------------------

While discard_max_hw_bytes is the hardware limit for the device, this

setting is the software limit. Some devices exhibit large latencies when

large discards are issued, setting this value lower will make Linux issue

smaller discards and potentially help reduce latencies induced by large

discard operations.



discard_zeroes_data (RO)

------------------------

When read, this file will show if the discarded block are zeroed by the

block/blk-settings.c

+4 −0
Original line number Diff line number Diff line
@@ -116,6 +116,7 @@ void blk_set_default_limits(struct queue_limits *lim) 
	lim->chunk_sectors = 0;

	lim->max_write_same_sectors = 0;

	lim->max_discard_sectors = 0;

	lim->max_hw_discard_sectors = 0;

	lim->discard_granularity = 0;

	lim->discard_alignment = 0;

	lim->discard_misaligned = 0;
@@ -303,6 +304,7 @@ EXPORT_SYMBOL(blk_queue_chunk_sectors); 
void blk_queue_max_discard_sectors(struct request_queue *q,

		unsigned int max_discard_sectors)

{

	q->limits.max_hw_discard_sectors = max_discard_sectors;

	q->limits.max_discard_sectors = max_discard_sectors;

}

EXPORT_SYMBOL(blk_queue_max_discard_sectors);
@@ -641,6 +643,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b, 


		t->max_discard_sectors = min_not_zero(t->max_discard_sectors,

						      b->max_discard_sectors);

		t->max_hw_discard_sectors = min_not_zero(t->max_hw_discard_sectors,

							 b->max_hw_discard_sectors);

		t->discard_granularity = max(t->discard_granularity,

					     b->discard_granularity);

		t->discard_alignment = lcm_not_zero(t->discard_alignment, alignment) %

block/blk-sysfs.c

+39 −1
Original line number Diff line number Diff line
@@ -145,12 +145,43 @@ static ssize_t queue_discard_granularity_show(struct request_queue *q, char *pag 
	return queue_var_show(q->limits.discard_granularity, page);

}



static ssize_t queue_discard_max_hw_show(struct request_queue *q, char *page)

{

	unsigned long long val;



	val = q->limits.max_hw_discard_sectors << 9;

	return sprintf(page, "%llu\n", val);

}



static ssize_t queue_discard_max_show(struct request_queue *q, char *page)

{

	return sprintf(page, "%llu\n",

		       (unsigned long long)q->limits.max_discard_sectors << 9);

}



static ssize_t queue_discard_max_store(struct request_queue *q,

				       const char *page, size_t count)

{

	unsigned long max_discard;

	ssize_t ret = queue_var_store(&max_discard, page, count);



	if (ret < 0)

		return ret;



	if (max_discard & (q->limits.discard_granularity - 1))

		return -EINVAL;



	max_discard >>= 9;

	if (max_discard > UINT_MAX)

		return -EINVAL;



	if (max_discard > q->limits.max_hw_discard_sectors)

		max_discard = q->limits.max_hw_discard_sectors;



	q->limits.max_discard_sectors = max_discard;

	return ret;

}



static ssize_t queue_discard_zeroes_data_show(struct request_queue *q, char *page)

{

	return queue_var_show(queue_discard_zeroes_data(q), page);
@@ -360,9 +391,15 @@ static struct queue_sysfs_entry queue_discard_granularity_entry = { 
	.show = queue_discard_granularity_show,

};



static struct queue_sysfs_entry queue_discard_max_hw_entry = {

	.attr = {.name = "discard_max_hw_bytes", .mode = S_IRUGO },

	.show = queue_discard_max_hw_show,

};



static struct queue_sysfs_entry queue_discard_max_entry = {

	.attr = {.name = "discard_max_bytes", .mode = S_IRUGO },

	.attr = {.name = "discard_max_bytes", .mode = S_IRUGO | S_IWUSR },

	.show = queue_discard_max_show,

	.store = queue_discard_max_store,

};



static struct queue_sysfs_entry queue_discard_zeroes_data_entry = {
@@ -421,6 +458,7 @@ static struct attribute *default_attrs[] = { 
	&queue_io_opt_entry.attr,

	&queue_discard_granularity_entry.attr,

	&queue_discard_max_entry.attr,

	&queue_discard_max_hw_entry.attr,

	&queue_discard_zeroes_data_entry.attr,

	&queue_write_same_max_entry.attr,

	&queue_nonrot_entry.attr,

include/linux/blkdev.h

+1 −0
Original line number Diff line number Diff line
@@ -268,6 +268,7 @@ struct queue_limits { 
	unsigned int		io_min;

	unsigned int		io_opt;

	unsigned int		max_discard_sectors;

	unsigned int		max_hw_discard_sectors;

	unsigned int		max_write_same_sectors;

	unsigned int		discard_granularity;

	unsigned int		discard_alignment;

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