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>

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 6d94e06..26904ff 100644 (file)
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -353,6 +353,12 @@ noauto_da_alloc            replacing existing files via patterns such as
                        system crashes before the delayed allocation
                        blocks are forced to disk.
 
+discard                Controls whether ext4 should issue discard/TRIM
+nodiscard(*)           commands to the underlying block device when
+                       blocks are freed.  This is useful for SSD devices
+                       and sparse/thinly-provisioned LUNs, but it is off
+                       by default until sufficient testing has been done.
+
 Data Mode
 =========
 There are 3 different data modes:

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8825515..05ce38b 100644 (file)
--- 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 bba1282..6e5a23a 100644 (file)
--- 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 f2d5ec7..2b382f6 100644 (file)
--- 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\" "