Currently we set the bio size to the byte equivalent of the blocks to
be trimmed when submitting the initial DISCARD ioctl. That means it
is subject to the max_hw_sectors limitation of the HBA which is
much lower than the size of a DISCARD request we can support.
Add a separate max_discard_sectors tunable to limit the size for discard
requests.
We limit the max discard request size in bytes to 32bit as that is the
limit for bio->bi_size. This could be much larger if we had a way to pass
that information through the block layer.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c 2009-09-17 12:15:20.485003934 -0300
+++ linux-2.6/block/blk-core.c 2009-09-17 12:23:33.018028602 -0300
@@ -1436,7 +1436,8 @@ static inline void __generic_make_reques
goto end_io;
}
- if (unlikely(nr_sectors > queue_max_hw_sectors(q))) {
+ if (unlikely(!bio_rw_flagged(bio, BIO_RW_DISCARD) &&
+ nr_sectors > queue_max_hw_sectors(q))) {
printk(KERN_ERR "bio too big device %s (%u > %u)\n",
bdevname(bio->bi_bdev, b),
bio_sectors(bio),
Index: linux-2.6/block/blk-settings.c
===================================================================
--- linux-2.6.orig/block/blk-settings.c 2009-09-17 12:15:20.494003963 -0300
+++ linux-2.6/block/blk-settings.c 2009-09-17 13:12:00.770254159 -0300
@@ -95,6 +95,7 @@ void blk_set_default_limits(struct queue
lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
lim->max_segment_size = MAX_SEGMENT_SIZE;
lim->max_sectors = lim->max_hw_sectors = SAFE_MAX_SECTORS;
+ lim->max_discard_sectors = SAFE_MAX_SECTORS;
lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);
lim->alignment_offset = 0;
@@ -237,6 +238,18 @@ void blk_queue_max_hw_sectors(struct req
EXPORT_SYMBOL(blk_queue_max_hw_sectors);
/**
+ * blk_queue_max_discard_sectors - set max sectors for a single discard
+ * @q: the request queue for the device
+ * @max_discard: maximum number of sectors to discard
+ **/
+void blk_queue_max_discard_sectors(struct request_queue *q,
+ unsigned int max_discard_sectors)
+{
+ q->limits.max_discard_sectors = max_discard_sectors;
+}
+EXPORT_SYMBOL(blk_queue_max_discard_sectors);
+
+/**
* blk_queue_max_phys_segments - set max phys segments for a request for this queue
* @q: the request queue for the device
* @max_segments: max number of segments
Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h 2009-09-17 12:15:20.542254662 -0300
+++ linux-2.6/include/linux/blkdev.h 2009-09-17 13:12:15.542006586 -0300
@@ -311,6 +311,7 @@ struct queue_limits {
unsigned int alignment_offset;
unsigned int io_min;
unsigned int io_opt;
+ unsigned int max_discard_sectors;
unsigned short logical_block_size;
unsigned short max_hw_segments;
@@ -928,6 +929,8 @@ extern void blk_queue_max_hw_sectors(str
extern void blk_queue_max_phys_segments(struct request_queue *, unsigned short);
extern void blk_queue_max_hw_segments(struct request_queue *, unsigned short);
extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
+extern void blk_queue_max_discard_sectors(struct request_queue *q,
+ unsigned int max_discard_sectors);
extern void blk_queue_logical_block_size(struct request_queue *, unsigned short);
extern void blk_queue_physical_block_size(struct request_queue *, unsigned short);
extern void blk_queue_alignment_offset(struct request_queue *q,
Index: linux-2.6/block/blk-barrier.c
===================================================================
--- linux-2.6.orig/block/blk-barrier.c 2009-09-17 12:19:18.659011091 -0300
+++ linux-2.6/block/blk-barrier.c 2009-09-17 12:31:05.660256438 -0300
@@ -385,6 +385,8 @@ int blkdev_issue_discard(struct block_de
while (nr_sects && !ret) {
unsigned int sector_size = q->limits.logical_block_size;
+ unsigned int max_discard_sectors =
+ min(q->limits.max_discard_sectors, UINT_MAX >> 9);
bio = bio_alloc(gfp_mask, 1);
if (!bio)
@@ -411,10 +413,10 @@ int blkdev_issue_discard(struct block_de
* touch many more blocks on disk than the actual payload
* length.
*/
- if (nr_sects > queue_max_hw_sectors(q)) {
- bio->bi_size = queue_max_hw_sectors(q) << 9;
- nr_sects -= queue_max_hw_sectors(q);
- sector += queue_max_hw_sectors(q);
+ if (nr_sects > max_discard_sectors) {
+ bio->bi_size = max_discard_sectors << 9;
+ nr_sects -= max_discard_sectors;
+ sector += max_discard_sectors;
} else {
bio->bi_size = nr_sects << 9;
nr_sects = 0;
--
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