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    Subject[PATCH 01/17] writeback: introduce wbc.tagged_sync for the WB_SYNC_NONE sync stage
    sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
    WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do
    livelock prevention for it, too.

    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.

    CC: Jan Kara <jack@suse.cz>
    CC: Dave Chinner <david@fromorbit.com>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    fs/ext4/inode.c | 4 ++--
    fs/fs-writeback.c | 9 +++++----
    include/linux/writeback.h | 1 +
    mm/page-writeback.c | 4 ++--
    4 files changed, 10 insertions(+), 8 deletions(-)

    --- linux-next.orig/fs/fs-writeback.c 2011-05-05 23:29:51.000000000 +0800
    +++ linux-next/fs/fs-writeback.c 2011-05-05 23:30:22.000000000 +0800
    @@ -36,6 +36,7 @@ struct wb_writeback_work {
    long nr_pages;
    struct super_block *sb;
    enum writeback_sync_modes sync_mode;
    + unsigned int tagged_sync: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_sync = work->tagged_sync,
    .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_sync)
    write_chunk = LONG_MAX;

    wbc.wb_start = jiffies; /* livelock avoidance */
    @@ -1193,6 +1193,7 @@ void writeback_inodes_sb_nr(struct super
    struct wb_writeback_work work = {
    .sb = sb,
    .sync_mode = WB_SYNC_NONE,
    + .tagged_sync = 1,
    .done = &done,
    .nr_pages = nr,
    };
    --- linux-next.orig/include/linux/writeback.h 2011-05-05 23:29:51.000000000 +0800
    +++ linux-next/include/linux/writeback.h 2011-05-05 23:30:22.000000000 +0800
    @@ -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_sync:1; /* do livelock prevention for sync */
    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 */
    --- linux-next.orig/mm/page-writeback.c 2011-05-05 23:29:51.000000000 +0800
    +++ linux-next/mm/page-writeback.c 2011-05-05 23:30:22.000000000 +0800
    @@ -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_sync)
    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_sync)
    tag_pages_for_writeback(mapping, index, end);
    done_index = index;
    while (!done && (index <= end)) {
    --- linux-next.orig/fs/ext4/inode.c 2011-05-05 23:29:51.000000000 +0800
    +++ linux-next/fs/ext4/inode.c 2011-05-05 23:30:22.000000000 +0800
    @@ -2741,7 +2741,7 @@ 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_sync)
    tag = PAGECACHE_TAG_TOWRITE;
    else
    tag = PAGECACHE_TAG_DIRTY;
    @@ -2975,7 +2975,7 @@ static int ext4_da_writepages(struct add
    }

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

    while (!ret && wbc->nr_to_write > 0) {



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