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    Subject[19/34] ext4: make trim/discard optional (and off by default)
    2.6.32-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    (cherry picked from commit 5328e635315734d42080de9a5a1ee87bf4cae0a4)

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    Documentation/filesystems/ext4.txt | 6 ++++++
    fs/ext4/ext4.h | 1 +
    fs/ext4/mballoc.c | 21 +++++++++++++--------
    fs/ext4/super.c | 14 +++++++++++++-
    4 files changed, 33 insertions(+), 9 deletions(-)

    --- a/Documentation/filesystems/ext4.txt
    +++ b/Documentation/filesystems/ext4.txt
    @@ -353,6 +353,12 @@ noauto_da_alloc replacing existing file
    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:
    --- 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
    --- a/fs/ext4/mballoc.c
    +++ b/fs/ext4/mballoc.c
    @@ -2529,7 +2529,6 @@ static void release_blocks_on_commit(jou
    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(jou
    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);
    }
    --- a/fs/ext4/super.c
    +++ b/fs/ext4/super.c
    @@ -899,6 +899,9 @@ static int ext4_show_options(struct seq_
    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\" "



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