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authorPaolo Bonzini <pbonzini@redhat.com>2012-08-02 09:48:50 +0200
committerJens Axboe <axboe@kernel.dk>2012-08-02 09:48:50 +0200
commitc6e666345e1b79c62ba82339cc7d55a89cb73f88 (patch)
tree9ffc17b7010ba16a18482d5f9057374dae90b669 /include/linux/blkdev.h
parentf6ff53d3611b564661896be23369b54d84941a0e (diff)
downloadvexpress-lsk-c6e666345e1b79c62ba82339cc7d55a89cb73f88.tar.gz
block: split discard into aligned requests
When a disk has large discard_granularity and small max_discard_sectors, discards are not split with optimal alignment. In the limit case of discard_granularity == max_discard_sectors, no request could be aligned correctly, so in fact you might end up with no discarded logical blocks at all. Another example that helps showing the condition in the patch is with discard_granularity == 64, max_discard_sectors == 128. A request that is submitted for 256 sectors 2..257 will be split in two: 2..129, 130..257. However, only 2 aligned blocks out of 3 are included in the request; 128..191 may be left intact and not discarded. With this patch, the first request will be truncated to ensure good alignment of what's left, and the split will be 2..127, 128..255, 256..257. The patch will also take into account the discard_alignment. At most one extra request will be introduced, because the first request will be reduced by at most granularity-1 sectors, and granularity must be less than max_discard_sectors. Subsequent requests will run on round_down(max_discard_sectors, granularity) sectors, as in the current code. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Acked-by: Vivek Goyal <vgoyal@redhat.com> Tested-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/blkdev.h')
-rw-r--r--include/linux/blkdev.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 4e72a9d4823..281516ae8b4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1139,6 +1139,16 @@ static inline int queue_limit_discard_alignment(struct queue_limits *lim, sector
& (lim->discard_granularity - 1);
}
+static inline int bdev_discard_alignment(struct block_device *bdev)
+{
+ struct request_queue *q = bdev_get_queue(bdev);
+
+ if (bdev != bdev->bd_contains)
+ return bdev->bd_part->discard_alignment;
+
+ return q->limits.discard_alignment;
+}
+
static inline unsigned int queue_discard_zeroes_data(struct request_queue *q)
{
if (q->limits.max_discard_sectors && q->limits.discard_zeroes_data == 1)