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>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index dfd7e6f..e5dd628 100644 (file)
--- 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 4aedbff..bf7782f 100644 (file)
--- 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 3fbbf07..939b68f 100644 (file)
--- 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;
                }