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>

1 files changed, 13 insertions, 8 deletions

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);
         }