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writeback: Separate out wb_get_lookup() from wb_get_create()

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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 <jack@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2019-08-26 09:06:54 -07:00 committed by Jens Axboe
parent 34f8fe501f
commit ed288dc0d4
2 changed files with 39 additions and 18 deletions
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2
include/linux/backing-dev.h
View file

@ -230,6 +230,8 @@ static inline int bdi_sched_wait(void *word)
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);

55
mm/backing-dev.c
View file

@ -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;