From: Jens Axboe Date: Tue, 14 Jul 2015 18:42:35 +0000 (-0600) Subject: block: by default, limit maximum discard size to 64MB X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=refs%2Fheads%2Fdiscard-rw;p=linux-2.6-block.git block: by default, limit maximum discard size to 64MB Lots of devices exhibit very high latencies for big discards, hurting reads and writes. By default, limit the max discard we will build to 64MB. This value has shown good results across a number of devices. This will potentially hurt discard throughput, from a provisioning point of view (when the user does mkfs.xfs, for instance, and mkfs issues a full device discard). If that becomes an issue, we could have different behavior for provisioning vs runtime discards. Signed-off-by: Jens Axboe --- diff --git a/block/blk-settings.c b/block/blk-settings.c index b38d8d723276..b98d26fcbf81 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -306,6 +306,8 @@ void blk_queue_max_discard_sectors(struct request_queue *q, { q->limits.max_hw_discard_sectors = max_discard_sectors; q->limits.max_discard_sectors = max_discard_sectors; + if (q->limits.max_discard_sectors > BLK_DISCARD_MAX_SECTORS) + q->limits.max_discard_sectors = BLK_DISCARD_MAX_SECTORS; } EXPORT_SYMBOL(blk_queue_max_discard_sectors); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 243f29e779ec..3a01b16397c4 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1141,6 +1141,11 @@ enum blk_default_limits { BLK_SAFE_MAX_SECTORS = 255, BLK_MAX_SEGMENT_SIZE = 65536, BLK_SEG_BOUNDARY_MASK = 0xFFFFFFFFUL, + + /* + * Default to max 64MB of discards, to keep latencies in check + */ + BLK_DISCARD_MAX_SECTORS = (64 * 1024 * 1024UL) >> 9, }; #define blkdev_entry_to_request(entry) list_entry((entry), struct request, queuelist)