From 089fa91bc51dc10da5a75a6d9fff77f186fccb23 Mon Sep 17 00:00:00 2001 From: Etienne Dechamps Date: Thu, 4 Oct 2012 10:38:55 +0200 Subject: [PATCH] Align DISCARD requests on zvols. Currently, when processing DISCARD requests, zvol_discard() calls dmu_free_long_range() with the precise offset and size of the request. Unfortunately, this is not optimal for requests that are not aligned to the zvol block boundaries. Indeed, in the case of an unaligned range, dnode_free_range() will zero out the unaligned parts. Not only is this useless since we are not freeing any space by doing so, it is also slow because it translates to a read-modify-write operation. This patch fixes the issue by rounding up the discard start offset to the next volume block boundary, and rounding down the discard end offset to the previous volume block boundary. Signed-off-by: Brian Behlendorf Closes #1010 --- module/zfs/zvol.c | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-) diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c index 5668e1dc0..b07476c42 100644 --- a/module/zfs/zvol.c +++ b/module/zfs/zvol.c @@ -597,8 +597,8 @@ zvol_discard(void *arg) struct request *req = (struct request *)arg; struct request_queue *q = req->q; zvol_state_t *zv = q->queuedata; - uint64_t offset = blk_rq_pos(req) << 9; - uint64_t size = blk_rq_bytes(req); + uint64_t start = blk_rq_pos(req) << 9; + uint64_t end = start + blk_rq_bytes(req); int error; rl_t *rl; @@ -610,19 +610,28 @@ zvol_discard(void *arg) ASSERT(!(current->flags & PF_NOFS)); current->flags |= PF_NOFS; - if (offset + size > zv->zv_volsize) { - blk_end_request(req, -EIO, size); + if (end > zv->zv_volsize) { + blk_end_request(req, -EIO, blk_rq_bytes(req)); goto out; } - if (size == 0) { - blk_end_request(req, 0, size); + /* + * Align the request to volume block boundaries. If we don't, + * then this will force dnode_free_range() to zero out the + * unaligned parts, which is slow (read-modify-write) and + * useless since we are not freeing any space by doing so. + */ + start = P2ROUNDUP(start, zv->zv_volblocksize); + end = P2ALIGN(end, zv->zv_volblocksize); + + if (start >= end) { + blk_end_request(req, 0, blk_rq_bytes(req)); goto out; } - rl = zfs_range_lock(&zv->zv_znode, offset, size, RL_WRITER); + rl = zfs_range_lock(&zv->zv_znode, start, end - start, RL_WRITER); - error = dmu_free_long_range(zv->zv_objset, ZVOL_OBJ, offset, size); + error = dmu_free_long_range(zv->zv_objset, ZVOL_OBJ, start, end - start); /* * TODO: maybe we should add the operation to the log. @@ -630,7 +639,7 @@ zvol_discard(void *arg) zfs_range_unlock(rl); - blk_end_request(req, -error, size); + blk_end_request(req, -error, blk_rq_bytes(req)); out: current->flags &= ~PF_NOFS; } -- 2.40.0