On Thu 15-08-19 12:58:23, Tejun Heo wrote:
> Separate out wb_get_lookup() which doesn't try to create one if there
> isn't already one from wb_get_create(). This will be used by later
> patches.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Looks good to me. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> include/linux/backing-dev.h | 2 +
> mm/backing-dev.c | 55 +++++++++++++++++++++++++++++---------------
> 2 files changed, 39 insertions(+), 18 deletions(-)
>
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -230,6 +230,8 @@ static inline int bdi_sched_wait(void *w
> struct bdi_writeback_congested *
> wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp);
> void wb_congested_put(struct bdi_writeback_congested *congested);
> +struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,
> + struct cgroup_subsys_state *memcg_css);
> struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
> struct cgroup_subsys_state *memcg_css,
> gfp_t gfp);
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -618,13 +618,12 @@ out_put:
> }
>
> /**
> - * wb_get_create - get wb for a given memcg, create if necessary
> + * wb_get_lookup - get wb for a given memcg
> * @bdi: target bdi
> * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
> - * @gfp: allocation mask to use
> *
> - * Try to get the wb for @memcg_css on @bdi. If it doesn't exist, try to
> - * create one. The returned wb has its refcount incremented.
> + * Try to get the wb for @memcg_css on @bdi. The returned wb has its
> + * refcount incremented.
> *
> * This function uses css_get() on @memcg_css and thus expects its refcnt
> * to be positive on invocation. IOW, rcu_read_lock() protection on
> @@ -641,6 +640,39 @@ out_put:
> * each lookup. On mismatch, the existing wb is discarded and a new one is
> * created.
> */
> +struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,
> + struct cgroup_subsys_state *memcg_css)
> +{
> + struct bdi_writeback *wb;
> +
> + if (!memcg_css->parent)
> + return &bdi->wb;
> +
> + rcu_read_lock();
> + wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
> + if (wb) {
> + struct cgroup_subsys_state *blkcg_css;
> +
> + /* see whether the blkcg association has changed */
> + blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
> + if (unlikely(wb->blkcg_css != blkcg_css || !wb_tryget(wb)))
> + wb = NULL;
> + css_put(blkcg_css);
> + }
> + rcu_read_unlock();
> +
> + return wb;
> +}
> +
> +/**
> + * wb_get_create - get wb for a given memcg, create if necessary
> + * @bdi: target bdi
> + * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
> + * @gfp: allocation mask to use
> + *
> + * Try to get the wb for @memcg_css on @bdi. If it doesn't exist, try to
> + * create one. See wb_get_lookup() for more details.
> + */
> struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
> struct cgroup_subsys_state *memcg_css,
> gfp_t gfp)
> @@ -653,20 +685,7 @@ struct bdi_writeback *wb_get_create(stru
> return &bdi->wb;
>
> do {
> - rcu_read_lock();
> - wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
> - if (wb) {
> - struct cgroup_subsys_state *blkcg_css;
> -
> - /* see whether the blkcg association has changed */
> - blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
> - &io_cgrp_subsys);
> - if (unlikely(wb->blkcg_css != blkcg_css ||
> - !wb_tryget(wb)))
> - wb = NULL;
> - css_put(blkcg_css);
> - }
> - rcu_read_unlock();
> + wb = wb_get_lookup(bdi, memcg_css);
> } while (!wb && !cgwb_create(bdi, memcg_css, gfp));
>
> return wb;
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
