From ed288dc0d4aa29f65bd25b31b5cb866aa5664ff9 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 26 Aug 2019 09:06:54 -0700 Subject: writeback: Separate out wb_get_lookup() from wb_get_create() 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. Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe --- mm/backing-dev.c | 55 +++++++++++++++++++++++++++++++++++++------------------ 1 file changed, 37 insertions(+), 18 deletions(-) (limited to 'mm/backing-dev.c') diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 612aa7c5ddbd..d9daa3e422d0 100644 --- 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(struct backing_dev_info *bdi, 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; -- cgit