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    Subject[PATCHv4 3/5] ext4: remove unnecessary superblock dirtying
    Date
    From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

    This patch changes the '__ext4_handle_dirty_super()' function which is used
    by ext4 to update the superblock via the journal in the following cases:

    1. When creating the first large file on a file system without
    EXT4_FEATURE_RO_COMPAT_LARGE_FILE feature.
    2. When re-sizing the file-system.
    3. When creating an xattr on a file-system without the
    EXT4_FEATURE_COMPAT_EXT_ATTR feature.
    4. When adding or deleting an orphan (because we update the 's_last_orphan'
    superblock field).

    This function, however, falls back to just marking the superblock as dirty
    if the file-system has no journal. This means that we delay the actual
    superblock I/O submission by 5 seconds (roughly speaking). Namely, the
    'sync_supers()' kernel thread will call 'ext4_write_super()' later, where
    we actually will submit the superblock down to the media.

    However:
    1. For cases 1-3 it does not add any value to delay the I/O submission. These
    events are rare and we may just commit submit the superblock for
    asynchronous I/O right away.
    2. For case 4 - similarly, not terribly frequent event in most of workloads.
    It should be good enough to just submit asynchronous superblock write-out.

    This patch also removes 's_dirt' condition on the unmount path because we never
    set it anymore, so we should not test it.

    Tested using xfstests for both journalled and non-journalled ext4.

    Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
    ---
    fs/ext4/ext4.h | 1 +
    fs/ext4/ext4_jbd2.c | 2 +-
    fs/ext4/super.c | 5 ++---
    3 files changed, 4 insertions(+), 4 deletions(-)

    diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
    index 0c4042e..b2439d5 100644
    --- a/fs/ext4/ext4.h
    +++ b/fs/ext4/ext4.h
    @@ -2041,6 +2041,7 @@ extern int ext4_superblock_csum_verify(struct super_block *sb,
    struct ext4_super_block *es);
    extern void ext4_superblock_csum_set(struct super_block *sb,
    struct ext4_super_block *es);
    +extern int ext4_commit_super(struct super_block *sb, int sync);
    extern void *ext4_kvmalloc(size_t size, gfp_t flags);
    extern void *ext4_kvzalloc(size_t size, gfp_t flags);
    extern void ext4_kvfree(void *ptr);
    diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
    index 90f7c2e..27354df 100644
    --- a/fs/ext4/ext4_jbd2.c
    +++ b/fs/ext4/ext4_jbd2.c
    @@ -156,6 +156,6 @@ int __ext4_handle_dirty_super(const char *where, unsigned int line,
    (struct ext4_super_block *)bh->b_data);
    mark_buffer_dirty(bh);
    } else
    - sb->s_dirt = 1;
    + err = ext4_commit_super(sb, 0);
    return err;
    }
    diff --git a/fs/ext4/super.c b/fs/ext4/super.c
    index eb7aa3e..9b26ba0 100644
    --- a/fs/ext4/super.c
    +++ b/fs/ext4/super.c
    @@ -63,7 +63,6 @@ static struct ext4_features *ext4_feat;
    static int ext4_load_journal(struct super_block *, struct ext4_super_block *,
    unsigned long journal_devnum);
    static int ext4_show_options(struct seq_file *seq, struct dentry *root);
    -static int ext4_commit_super(struct super_block *sb, int sync);
    static void ext4_mark_recovery_complete(struct super_block *sb,
    struct ext4_super_block *es);
    static void ext4_clear_journal_err(struct super_block *sb,
    @@ -896,7 +895,7 @@ static void ext4_put_super(struct super_block *sb)
    EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
    es->s_state = cpu_to_le16(sbi->s_mount_state);
    }
    - if (sb->s_dirt || !(sb->s_flags & MS_RDONLY))
    + if (!(sb->s_flags & MS_RDONLY))
    ext4_commit_super(sb, 1);

    if (sbi->s_proc) {
    @@ -4155,7 +4154,7 @@ static int ext4_load_journal(struct super_block *sb,
    return 0;
    }

    -static int ext4_commit_super(struct super_block *sb, int sync)
    +int ext4_commit_super(struct super_block *sb, int sync)
    {
    struct ext4_super_block *es = EXT4_SB(sb)->s_es;
    struct buffer_head *sbh = EXT4_SB(sb)->s_sbh;
    --
    1.7.7.6


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