From 0034af036554c39eefd14d835a8ec3496ac46712 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 16 Jul 2015 09:14:26 -0600 Subject: [PATCH] block: make /sys/block//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: Jeff Moyer Signed-off-by: Jens Axboe --- Documentation/block/queue-sysfs.txt | 10 +++++++- block/blk-settings.c | 4 +++ block/blk-sysfs.c | 40 ++++++++++++++++++++++++++++- include/linux/blkdev.h | 1 + 4 files changed, 53 insertions(+), 2 deletions(-) diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt index 3a29f8914df9..e5d914845be6 100644 --- a/Documentation/block/queue-sysfs.txt +++ b/Documentation/block/queue-sysfs.txt @@ -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 diff --git a/block/blk-settings.c b/block/blk-settings.c index 12600bfffca9..b38d8d723276 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -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) % diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 6264b382d4d1..b1f34e463c0f 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -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, diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index d4068c17d0df..243f29e779ec 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -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;