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    Subject[PATCH V4 6/7] loop: use xarray to store workers
    Date
    css->id is unique in io controller wide, so replace rbtree with xarray
    for querying/storing 'blkcg_css' by using css->id as key, then code is
    simplified a lot.

    Acked-by: Dan Schatzberg <schatzberg.dan@gmail.com>
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    ---
    drivers/block/loop.c | 45 ++++++++++++++++++++++----------------------
    drivers/block/loop.h | 3 ++-
    2 files changed, 25 insertions(+), 23 deletions(-)

    diff --git a/drivers/block/loop.c b/drivers/block/loop.c
    index c322d6468ee7..f77fa9e5eb49 100644
    --- a/drivers/block/loop.c
    +++ b/drivers/block/loop.c
    @@ -971,7 +971,6 @@ static void loop_config_discard(struct loop_device *lo)
    }

    struct loop_worker {
    - struct rb_node rb_node;
    struct work_struct work;
    struct list_head cmd_list;
    struct list_head idle_list;
    @@ -998,6 +997,10 @@ static struct cgroup_subsys_state *loop_rq_blkcg_css(struct loop_cmd *cmd)
    return &blkcg->css;
    return NULL;
    }
    +static int loop_blkcg_css_id(struct cgroup_subsys_state *css)
    +{
    + return css->id;
    +}
    #else
    static inline int queue_on_root_worker(struct cgroup_subsys_state *css)
    {
    @@ -1007,6 +1010,10 @@ static struct cgroup_subsys_state *loop_rq_blkcg_css(struct loop_cmd *cmd)
    {
    return NULL;
    }
    +static int loop_blkcg_css_id(struct cgroup_subsys_state *css)
    +{
    + return 0;
    +}
    #endif

    static struct cgroup_subsys_state *loop_rq_get_memcg_css(
    @@ -1019,35 +1026,23 @@ static struct cgroup_subsys_state *loop_rq_get_memcg_css(

    static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
    {
    - struct rb_node **node = &(lo->worker_tree.rb_node), *parent = NULL;
    - struct loop_worker *cur_worker, *worker = NULL;
    + struct loop_worker *worker = NULL;
    struct work_struct *work;
    struct list_head *cmd_list;
    struct cgroup_subsys_state *blkcg_css = loop_rq_blkcg_css(cmd);
    + gfp_t gfp = GFP_NOWAIT | __GFP_NOWARN;

    spin_lock(&lo->lo_work_lock);

    if (queue_on_root_worker(blkcg_css))
    goto queue_work;

    - node = &lo->worker_tree.rb_node;
    -
    - while (*node) {
    - parent = *node;
    - cur_worker = container_of(*node, struct loop_worker, rb_node);
    - if (cur_worker->blkcg_css == blkcg_css) {
    - worker = cur_worker;
    - break;
    - } else if ((long)cur_worker->blkcg_css < (long)blkcg_css) {
    - node = &(*node)->rb_left;
    - } else {
    - node = &(*node)->rb_right;
    - }
    - }
    + /* css->id is unique in each cgroup subsystem */
    + worker = xa_load(&lo->workers, loop_blkcg_css_id(blkcg_css));
    if (worker)
    goto queue_work;

    - worker = kzalloc(sizeof(struct loop_worker), GFP_NOWAIT | __GFP_NOWARN);
    + worker = kzalloc(sizeof(*worker), gfp);
    /*
    * In the event we cannot allocate a worker, just queue on the
    * rootcg worker and issue the I/O as the rootcg
    @@ -1061,8 +1056,13 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
    INIT_LIST_HEAD(&worker->cmd_list);
    INIT_LIST_HEAD(&worker->idle_list);
    worker->lo = lo;
    - rb_link_node(&worker->rb_node, parent, node);
    - rb_insert_color(&worker->rb_node, &lo->worker_tree);
    +
    + if (xa_err(xa_store(&lo->workers, loop_blkcg_css_id(blkcg_css),
    + worker, gfp))) {
    + kfree(worker);
    + worker = NULL;
    + }
    +
    queue_work:
    if (worker) {
    /*
    @@ -1218,7 +1218,7 @@ static void __loop_free_idle_workers(struct loop_device *lo, bool force)
    LOOP_IDLE_WORKER_TIMEOUT))
    break;
    list_del(&worker->idle_list);
    - rb_erase(&worker->rb_node, &lo->worker_tree);
    + xa_erase(&lo->workers, loop_blkcg_css_id(worker->blkcg_css));
    css_put(worker->blkcg_css);
    kfree(worker);
    }
    @@ -1314,7 +1314,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
    INIT_WORK(&lo->rootcg_work, loop_rootcg_workfn);
    INIT_LIST_HEAD(&lo->rootcg_cmd_list);
    INIT_LIST_HEAD(&lo->idle_worker_list);
    - lo->worker_tree = RB_ROOT;
    + xa_init(&lo->workers);
    INIT_DELAYED_WORK(&lo->idle_work, loop_free_idle_workers);
    lo->use_dio = lo->lo_flags & LO_FLAGS_DIRECT_IO;
    lo->lo_device = bdev;
    @@ -1416,6 +1416,7 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
    destroy_workqueue(lo->workqueue);
    __loop_free_idle_workers(lo, true);
    cancel_delayed_work_sync(&lo->idle_work);
    + xa_destroy(&lo->workers);

    spin_lock_irq(&lo->lo_lock);
    lo->lo_backing_file = NULL;
    diff --git a/drivers/block/loop.h b/drivers/block/loop.h
    index 9df889af1bcf..cab34da1e1bb 100644
    --- a/drivers/block/loop.h
    +++ b/drivers/block/loop.h
    @@ -14,6 +14,7 @@
    #include <linux/blk-mq.h>
    #include <linux/spinlock.h>
    #include <linux/mutex.h>
    +#include <linux/xarray.h>
    #include <uapi/linux/loop.h>

    /* Possible states of device */
    @@ -59,7 +60,7 @@ struct loop_device {
    struct work_struct rootcg_work;
    struct list_head rootcg_cmd_list;
    struct list_head idle_worker_list;
    - struct rb_root worker_tree;
    + struct xarray workers;
    struct delayed_work idle_work;
    bool use_dio;
    bool sysfs_inited;
    --
    2.31.1
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