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    Subject[PATCH 10/17] writeback: avoid extra sync work at enqueue time
    This removes writeback_control.wb_start and does more straightforward
    sync livelock prevention by setting .older_than_this to prevent extra
    inodes from being enqueued in the first place.

    CC: Jan Kara <jack@suse.cz>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    fs/fs-writeback.c | 16 +++-------------
    include/linux/writeback.h | 3 ---
    2 files changed, 3 insertions(+), 16 deletions(-)

    --- linux-next.orig/fs/fs-writeback.c 2011-05-05 23:30:29.000000000 +0800
    +++ linux-next/fs/fs-writeback.c 2011-05-05 23:30:30.000000000 +0800
    @@ -544,15 +544,6 @@ static int writeback_sb_inodes(struct su
    continue;
    }

    - /*
    - * Was this inode dirtied after sync_sb_inodes was called?
    - * This keeps sync from extra jobs and livelock.
    - */
    - if (inode_dirtied_after(inode, wbc->wb_start)) {
    - spin_unlock(&inode->i_lock);
    - return 1;
    - }
    -
    __iget(inode);

    pages_skipped = wbc->pages_skipped;
    @@ -585,9 +576,6 @@ static void __writeback_inodes_wb(struct
    {
    int ret = 0;

    - if (!wbc->wb_start)
    - wbc->wb_start = jiffies; /* livelock avoidance */
    -
    while (!list_empty(&wb->b_io)) {
    struct inode *inode = wb_inode(wb->b_io.prev);
    struct super_block *sb = inode->i_sb;
    @@ -686,7 +674,9 @@ static long wb_writeback(struct bdi_writ
    if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_sync)
    write_chunk = LONG_MAX;

    - wbc.wb_start = jiffies; /* livelock avoidance */
    + oldest_jif = jiffies;
    + wbc.older_than_this = &oldest_jif;
    +
    for (;;) {
    /*
    * Stop writeback when nr_pages has been consumed
    --- linux-next.orig/include/linux/writeback.h 2011-05-05 23:30:28.000000000 +0800
    +++ linux-next/include/linux/writeback.h 2011-05-05 23:30:30.000000000 +0800
    @@ -26,9 +26,6 @@ struct writeback_control {
    enum writeback_sync_modes sync_mode;
    unsigned long *older_than_this; /* If !NULL, only write back inodes
    older than this */
    - unsigned long wb_start; /* Time writeback_inodes_wb was
    - called. This is needed to avoid
    - extra jobs and livelock */
    long nr_to_write; /* Write this many pages, and decrement
    this for each page written */
    long pages_skipped; /* Pages which were not written */



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