ext4: make trim/discard optional (and off by default)

It is anticipated that when sb_issue_discard starts doing
real work on trim-capable devices, we may see issues.  Make
this mount-time optional, and default it to off until we know
that things are working out OK.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

3 files changed, 27 insertions, 9 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8825515eeddd..05ce38b981cb 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -750,6 +750,7 @@ struct ext4_inode_info {
 #define EXT4_MOUNT_DELALLOC             0x8000000 /* Delalloc support */
 #define EXT4_MOUNT_DATA_ERR_ABORT       0x10000000 /* Abort on file data write */
 #define EXT4_MOUNT_BLOCK_VALIDITY       0x20000000 /* Block validity checking */
+#define EXT4_MOUNT_DISCARD              0x40000000 /* Issue DISCARD requests */
 
 #define clear_opt(o, opt)               o &= ~EXT4_MOUNT_##opt
 #define set_opt(o, opt)                 o |= EXT4_MOUNT_##opt
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index bba12824defa..6e5a23a2cc25 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2529,7 +2529,6 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
         struct ext4_group_info *db;
         int err, count = 0, count2 = 0;
         struct ext4_free_data *entry;
-        ext4_fsblk_t discard_block;
         struct list_head *l, *ltmp;
 
         list_for_each_safe(l, ltmp, &txn->t_private_list) {
@@ -2559,13 +2558,19 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
                         page_cache_release(e4b.bd_bitmap_page);
                 }
                 ext4_unlock_group(sb, entry->group);
-                discard_block = (ext4_fsblk_t) entry->group * EXT4_BLOCKS_PER_GROUP(sb)
-                        + entry->start_blk
-                        + le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
-                trace_ext4_discard_blocks(sb, (unsigned long long)discard_block,
-                                          entry->count);
-                sb_issue_discard(sb, discard_block, entry->count);
-
+                if (test_opt(sb, DISCARD)) {
+                        ext4_fsblk_t discard_block;
+                        struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+
+                        discard_block = (ext4_fsblk_t)entry->group *
+                                                EXT4_BLOCKS_PER_GROUP(sb)
+                                        + entry->start_blk
+                                        + le32_to_cpu(es->s_first_data_block);
+                        trace_ext4_discard_blocks(sb,
+                                        (unsigned long long)discard_block,
+                                        entry->count);
+                        sb_issue_discard(sb, discard_block, entry->count);
+                }
                 kmem_cache_free(ext4_free_ext_cachep, entry);
                 ext4_mb_release_desc(&e4b);
         }
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index f2d5ec77c1e9..2b382f6f80c1 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -899,6 +899,9 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
         if (test_opt(sb, NO_AUTO_DA_ALLOC))
                 seq_puts(seq, ",noauto_da_alloc");
 
+        if (test_opt(sb, DISCARD))
+                seq_puts(seq, ",discard");
+
         ext4_show_quota_options(seq, sb);
 
         return 0;
@@ -1079,7 +1082,8 @@ enum {
         Opt_usrquota, Opt_grpquota, Opt_i_version,
         Opt_stripe, Opt_delalloc, Opt_nodelalloc,
         Opt_block_validity, Opt_noblock_validity,
-        Opt_inode_readahead_blks, Opt_journal_ioprio
+        Opt_inode_readahead_blks, Opt_journal_ioprio,
+        Opt_discard, Opt_nodiscard,
 };
 
 static const match_table_t tokens = {
@@ -1144,6 +1148,8 @@ static const match_table_t tokens = {
         {Opt_auto_da_alloc, "auto_da_alloc=%u"},
         {Opt_auto_da_alloc, "auto_da_alloc"},
         {Opt_noauto_da_alloc, "noauto_da_alloc"},
+        {Opt_discard, "discard"},
+        {Opt_nodiscard, "nodiscard"},
         {Opt_err, NULL},
 };
 
@@ -1565,6 +1571,12 @@ set_qf_format:
                         else
                                 set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
                         break;
+                case Opt_discard:
+                        set_opt(sbi->s_mount_opt, DISCARD);
+                        break;
+                case Opt_nodiscard:
+                        clear_opt(sbi->s_mount_opt, DISCARD);
+                        break;
                 default:
                         ext4_msg(sb, KERN_ERR,
                                "Unrecognized mount option \"%s\" "