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    Subject[PATCH 24/51] writeback, blkcg: associate each blkcg_gq with the corresponding bdi_writeback_congested
    Date
    A blkg (blkcg_gq) can be congested and decongested independently from
    other blkgs on the same request_queue. Accordingly, for cgroup
    writeback support, the congestion status at bdi (backing_dev_info)
    should be split and updated separately from matching blkg's.

    This patch prepares by adding blkg->wb_congested and associating a
    blkg with its matching per-blkcg bdi_writeback_congested on creation.

    v2: Updated to associate bdi_writeback_congested instead of
    bdi_writeback.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    ---
    block/blk-cgroup.c | 17 +++++++++++++++--
    include/linux/blk-cgroup.h | 6 ++++++
    2 files changed, 21 insertions(+), 2 deletions(-)

    diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
    index 979cfdb..31610ae 100644
    --- a/block/blk-cgroup.c
    +++ b/block/blk-cgroup.c
    @@ -182,6 +182,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
    struct blkcg_gq *new_blkg)
    {
    struct blkcg_gq *blkg;
    + struct bdi_writeback_congested *wb_congested;
    int i, ret;

    WARN_ON_ONCE(!rcu_read_lock_held());
    @@ -193,22 +194,30 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
    goto err_free_blkg;
    }

    + wb_congested = wb_congested_get_create(&q->backing_dev_info,
    + blkcg->css.id, GFP_ATOMIC);
    + if (!wb_congested) {
    + ret = -ENOMEM;
    + goto err_put_css;
    + }
    +
    /* allocate */
    if (!new_blkg) {
    new_blkg = blkg_alloc(blkcg, q, GFP_ATOMIC);
    if (unlikely(!new_blkg)) {
    ret = -ENOMEM;
    - goto err_put_css;
    + goto err_put_congested;
    }
    }
    blkg = new_blkg;
    + blkg->wb_congested = wb_congested;

    /* link parent */
    if (blkcg_parent(blkcg)) {
    blkg->parent = __blkg_lookup(blkcg_parent(blkcg), q, false);
    if (WARN_ON_ONCE(!blkg->parent)) {
    ret = -EINVAL;
    - goto err_put_css;
    + goto err_put_congested;
    }
    blkg_get(blkg->parent);
    }
    @@ -245,6 +254,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
    blkg_put(blkg);
    return ERR_PTR(ret);

    +err_put_congested:
    + wb_congested_put(wb_congested);
    err_put_css:
    css_put(&blkcg->css);
    err_free_blkg:
    @@ -391,6 +402,8 @@ void __blkg_release_rcu(struct rcu_head *rcu_head)
    if (blkg->parent)
    blkg_put(blkg->parent);

    + wb_congested_put(blkg->wb_congested);
    +
    blkg_free(blkg);
    }
    EXPORT_SYMBOL_GPL(__blkg_release_rcu);
    diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
    index 3033eb1..07a32b8 100644
    --- a/include/linux/blk-cgroup.h
    +++ b/include/linux/blk-cgroup.h
    @@ -99,6 +99,12 @@ struct blkcg_gq {
    struct hlist_node blkcg_node;
    struct blkcg *blkcg;

    + /*
    + * Each blkg gets congested separately and the congestion state is
    + * propagated to the matching bdi_writeback_congested.
    + */
    + struct bdi_writeback_congested *wb_congested;
    +
    /* all non-root blkcg_gq's are guaranteed to have access to parent */
    struct blkcg_gq *parent;

    --
    2.4.0


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