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    Subject[RFC][PATCH 06/16] writeback: improve bdi_has_dirty_io
    Date
    From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

    This patch is of clean-up type. Currently the purpose of the
    'bdi_has_dirty_io()' function is not very clear - it is equivalent
    to 'wb_has_dirty_io()' and there is little point for it to exist.
    It is used inconsistently as well, e.g., in 'bdi_forker_thread()'
    we use

    if (wb_has_dirty_io() || !list_empty(&me->bdi->work_list))

    but in the other place we use another construct to achieve the
    essentially same goal:

    if (!bdi_has_dirty_io(bdi) && list_empty(&bdi->work_list))

    which is inconsistent and make code more difficult to follow.

    This patch changes semantics of 'bdi_has_dirty_io()' a bit, and now
    it checks for dirty io _and_ bdi works. The code which needs to check
    only dirty inodes can use 'wb_has_dirty_io()'. This makes the bdi
    forker code a bit nicer, and justifies the existence of
    'bdi_has_dirty_io()'.

    Just a small cleanup.

    Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
    ---
    fs/fs-writeback.c | 2 +-
    mm/backing-dev.c | 10 +++++-----
    2 files changed, 6 insertions(+), 6 deletions(-)

    diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
    index 5e6b7fc..3fc5194 100644
    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -891,7 +891,7 @@ void wakeup_flusher_threads(long nr_pages)

    rcu_read_lock();
    list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
    - if (!bdi_has_dirty_io(bdi))
    + if (!wb_has_dirty_io(&bdi->wb))
    continue;
    __bdi_start_writeback(bdi, nr_pages, false, false);
    }
    diff --git a/mm/backing-dev.c b/mm/backing-dev.c
    index 8be2e13..03a3d82 100644
    --- a/mm/backing-dev.c
    +++ b/mm/backing-dev.c
    @@ -263,7 +263,8 @@ static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)

    int bdi_has_dirty_io(struct backing_dev_info *bdi)
    {
    - return wb_has_dirty_io(&bdi->wb);
    + return wb_has_dirty_io(&bdi->wb) ||
    + !list_empty(&bdi->work_list);
    }

    static void bdi_flush_io(struct backing_dev_info *bdi)
    @@ -338,7 +339,7 @@ static int bdi_forker_thread(void *ptr)
    * Temporary measure, we want to make sure we don't see
    * dirty data on the default backing_dev_info
    */
    - if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
    + if (bdi_has_dirty_io(me->bdi))
    wb_do_writeback(me, 0);

    spin_lock_bh(&bdi_lock);
    @@ -350,8 +351,7 @@ static int bdi_forker_thread(void *ptr)
    list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
    if (bdi->wb.task)
    continue;
    - if (list_empty(&bdi->work_list) &&
    - !bdi_has_dirty_io(bdi))
    + if (!bdi_has_dirty_io(bdi))
    continue;

    bdi_add_default_flusher_thread(bdi);
    @@ -637,7 +637,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
    * Splice our entries to the default_backing_dev_info, if this
    * bdi disappears
    */
    - if (bdi_has_dirty_io(bdi)) {
    + if (wb_has_dirty_io(&bdi->wb)) {
    struct bdi_writeback *dst = &default_backing_dev_info.wb;

    spin_lock(&inode_lock);
    --
    1.7.1.1


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