Btrfs: add -o discard option

Enable discard by default is not a good idea given the the trim speed
of SSD prototypes we've seen, and the carecteristics for many high-end
arrays.  Turn of discards by default and require the -o discard option
to enable them on.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

3 files changed, 10 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index dfd7e6fc66d..e5dd628a526 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1153,6 +1153,7 @@ struct btrfs_root {
 #define BTRFS_MOUNT_FLUSHONCOMMIT       (1 << 7)
 #define BTRFS_MOUNT_SSD_SPREAD          (1 << 8)
 #define BTRFS_MOUNT_NOSSD               (1 << 9)
+#define BTRFS_MOUNT_DISCARD             (1 << 10)
 
 #define btrfs_clear_opt(o, opt)         ((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)           ((o) |= BTRFS_MOUNT_##opt)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4aedbff36b8..bf7782fc593 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1584,6 +1584,9 @@ static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
         u64 map_length = num_bytes;
         struct btrfs_multi_bio *multi = NULL;
 
+        if (!btrfs_test_opt(root, DISCARD))
+                return 0;
+
         /* Tell the block device(s) that the sectors can be discarded */
         ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
                               bytenr, &map_length, &multi, 0);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3fbbf0761ac..939b68f0612 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -66,7 +66,8 @@ enum {
         Opt_degraded, Opt_subvol, Opt_device, Opt_nodatasum, Opt_nodatacow,
         Opt_max_extent, Opt_max_inline, Opt_alloc_start, Opt_nobarrier,
         Opt_ssd, Opt_nossd, Opt_ssd_spread, Opt_thread_pool, Opt_noacl,
-        Opt_compress, Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_err,
+        Opt_compress, Opt_notreelog, Opt_ratio, Opt_flushoncommit,
+        Opt_discard, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -88,6 +89,7 @@ static match_table_t tokens = {
         {Opt_notreelog, "notreelog"},
         {Opt_flushoncommit, "flushoncommit"},
         {Opt_ratio, "metadata_ratio=%d"},
+        {Opt_discard, "discard"},
         {Opt_err, NULL},
 };
 
@@ -257,6 +259,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                                        info->metadata_ratio);
                         }
                         break;
+                case Opt_discard:
+                        btrfs_set_opt(info->mount_opt, DISCARD);
+                        break;
                 default:
                         break;
                 }