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    SubjectRe: [PATCH 05/10] block: remove per-queue plugging
    On Mon, 18 Apr 2011 08:19:22 +1000 NeilBrown <neilb@suse.de> wrote:

    > So can we please have my original patch applied? (Revised version using
    > list_splice_init included below).

    I hadn't adjusted that one properly for the recent code shuffling.
    This one is actually tested...

    Thanks,
    NeilBrown

    From 325b1c12b6165002022bd7b599f95c0331491cb3 Mon Sep 17 00:00:00 2001
    From: NeilBrown <neilb@suse.de>
    Date: Mon, 18 Apr 2011 14:06:05 +1000
    Subject: [PATCH] Enhance new plugging support to support general callbacks.

    md/raid requires an unplug callback, but as it does not uses
    requests the current code cannot provide one.

    So allow arbitrary callbacks to be attached to the blk_plug.

    Cc: Jens Axboe <jaxboe@fusionio.com>
    Signed-off-by: NeilBrown <neilb@suse.de>
    ---
    block/blk-core.c | 20 ++++++++++++++++++++
    include/linux/blkdev.h | 7 ++++++-
    2 files changed, 26 insertions(+), 1 deletions(-)

    diff --git a/block/blk-core.c b/block/blk-core.c
    index 78b7b0c..77edf05 100644
    --- a/block/blk-core.c
    +++ b/block/blk-core.c
    @@ -2638,6 +2638,7 @@ void blk_start_plug(struct blk_plug *plug)

    plug->magic = PLUG_MAGIC;
    INIT_LIST_HEAD(&plug->list);
    + INIT_LIST_HEAD(&plug->cb_list);
    plug->should_sort = 0;

    /*
    @@ -2678,6 +2679,24 @@ static void queue_unplugged(struct request_queue *q, unsigned int depth,
    q->unplugged_fn(q);
    }

    +static void flush_plug_callbacks(struct blk_plug *plug)
    +{
    + LIST_HEAD(callbacks);
    +
    + if (list_empty(&plug->cb_list))
    + return;
    +
    + list_splice_init(&plug->cb_list, &callbacks);
    +
    + while (!list_empty(&callbacks)) {
    + struct blk_plug_cb *cb = list_first_entry(&callbacks,
    + struct blk_plug_cb,
    + list);
    + list_del(&cb->list);
    + cb->callback(cb);
    + }
    +}
    +
    void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
    {
    struct request_queue *q;
    @@ -2688,6 +2707,7 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)

    BUG_ON(plug->magic != PLUG_MAGIC);

    + flush_plug_callbacks(plug);
    if (list_empty(&plug->list))
    return;

    diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
    index ec0357d..f3f7879 100644
    --- a/include/linux/blkdev.h
    +++ b/include/linux/blkdev.h
    @@ -860,8 +860,13 @@ extern void blk_put_queue(struct request_queue *);
    struct blk_plug {
    unsigned long magic;
    struct list_head list;
    + struct list_head cb_list;
    unsigned int should_sort;
    };
    +struct blk_plug_cb {
    + struct list_head list;
    + void (*callback)(struct blk_plug_cb *);
    +};

    extern void blk_start_plug(struct blk_plug *);
    extern void blk_finish_plug(struct blk_plug *);
    @@ -887,7 +892,7 @@ static inline bool blk_needs_flush_plug(struct task_struct *tsk)
    {
    struct blk_plug *plug = tsk->plug;

    - return plug && !list_empty(&plug->list);
    + return plug && (!list_empty(&plug->list) || !list_empty(&plug->cb_list));
    }

    /*
    --
    1.7.3.4


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