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    Subject[160/244] writeback: introduce .tagged_writepages for the WB_SYNC_NONE sync stage
    3.0-stable review patch.  If anyone has any objections, please let us know.

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

    From: Wu Fengguang <fengguang.wu@intel.com>

    commit 6e6938b6d3130305a5960c86b1a9b21e58cf6144 upstream.

    sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
    WB_SYNC_ALL sync. Identify the first stage with .tagged_writepages and
    do livelock prevention for it, too.

    Jan's commit f446daaea9 ("mm: implement writeback livelock avoidance
    using page tagging") is a partial fix in that it only fixed the
    WB_SYNC_ALL phase livelock.

    Although ext4 is tested to no longer livelock with commit f446daaea9,
    it may due to some "redirty_tail() after pages_skipped" effect which
    is by no means a guarantee for _all_ the file systems.

    Note that writeback_inodes_sb() is called by not only sync(), they are
    treated the same because the other callers also need livelock prevention.

    Impact: It changes the order in which pages/inodes are synced to disk.
    Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
    until finished with the current inode.

    Acked-by: Jan Kara <jack@suse.cz>
    CC: Dave Chinner <david@fromorbit.com>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/ext4/inode.c | 4 ++--
    fs/fs-writeback.c | 17 +++++++++--------
    include/linux/writeback.h | 1 +
    mm/page-writeback.c | 4 ++--
    4 files changed, 14 insertions(+), 12 deletions(-)

    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -2756,7 +2756,7 @@ static int write_cache_pages_da(struct a
    index = wbc->range_start >> PAGE_CACHE_SHIFT;
    end = wbc->range_end >> PAGE_CACHE_SHIFT;

    - if (wbc->sync_mode == WB_SYNC_ALL)
    + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
    tag = PAGECACHE_TAG_TOWRITE;
    else
    tag = PAGECACHE_TAG_DIRTY;
    @@ -2988,7 +2988,7 @@ static int ext4_da_writepages(struct add
    }

    retry:
    - if (wbc->sync_mode == WB_SYNC_ALL)
    + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
    tag_pages_for_writeback(mapping, index, end);

    while (!ret && wbc->nr_to_write > 0) {
    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -36,6 +36,7 @@ struct wb_writeback_work {
    long nr_pages;
    struct super_block *sb;
    enum writeback_sync_modes sync_mode;
    + unsigned int tagged_writepages:1;
    unsigned int for_kupdate:1;
    unsigned int range_cyclic:1;
    unsigned int for_background:1;
    @@ -650,6 +651,7 @@ static long wb_writeback(struct bdi_writ
    {
    struct writeback_control wbc = {
    .sync_mode = work->sync_mode,
    + .tagged_writepages = work->tagged_writepages,
    .older_than_this = NULL,
    .for_kupdate = work->for_kupdate,
    .for_background = work->for_background,
    @@ -657,7 +659,7 @@ static long wb_writeback(struct bdi_writ
    };
    unsigned long oldest_jif;
    long wrote = 0;
    - long write_chunk;
    + long write_chunk = MAX_WRITEBACK_PAGES;
    struct inode *inode;

    if (wbc.for_kupdate) {
    @@ -683,9 +685,7 @@ static long wb_writeback(struct bdi_writ
    * (quickly) tag currently dirty pages
    * (maybe slowly) sync all tagged pages
    */
    - if (wbc.sync_mode == WB_SYNC_NONE)
    - write_chunk = MAX_WRITEBACK_PAGES;
    - else
    + if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_writepages)
    write_chunk = LONG_MAX;

    wbc.wb_start = jiffies; /* livelock avoidance */
    @@ -1188,10 +1188,11 @@ void writeback_inodes_sb_nr(struct super
    {
    DECLARE_COMPLETION_ONSTACK(done);
    struct wb_writeback_work work = {
    - .sb = sb,
    - .sync_mode = WB_SYNC_NONE,
    - .done = &done,
    - .nr_pages = nr,
    + .sb = sb,
    + .sync_mode = WB_SYNC_NONE,
    + .tagged_writepages = 1,
    + .done = &done,
    + .nr_pages = nr,
    };

    WARN_ON(!rwsem_is_locked(&sb->s_umount));
    --- a/include/linux/writeback.h
    +++ b/include/linux/writeback.h
    @@ -47,6 +47,7 @@ struct writeback_control {
    unsigned encountered_congestion:1; /* An output: a queue is full */
    unsigned for_kupdate:1; /* A kupdate writeback */
    unsigned for_background:1; /* A background writeback */
    + unsigned tagged_writepages:1; /* tag-and-write to avoid livelock */
    unsigned for_reclaim:1; /* Invoked from the page allocator */
    unsigned range_cyclic:1; /* range_start is cyclic */
    unsigned more_io:1; /* more io to be dispatched */
    --- a/mm/page-writeback.c
    +++ b/mm/page-writeback.c
    @@ -892,12 +892,12 @@ int write_cache_pages(struct address_spa
    range_whole = 1;
    cycled = 1; /* ignore range_cyclic tests */
    }
    - if (wbc->sync_mode == WB_SYNC_ALL)
    + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
    tag = PAGECACHE_TAG_TOWRITE;
    else
    tag = PAGECACHE_TAG_DIRTY;
    retry:
    - if (wbc->sync_mode == WB_SYNC_ALL)
    + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
    tag_pages_for_writeback(mapping, index, end);
    done_index = index;
    while (!done && (index <= end)) {



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