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Commit ed288dc0 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

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: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 34f8fe50

include/linux/backing-dev.h

+2 −0
Original line number Diff line number Diff line
@@ -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);

mm/backing-dev.c

+37 −18
Original line number Diff line number Diff line
@@ -618,13 +618,12 @@ static int cgwb_create(struct backing_dev_info *bdi, 
}



/**

 * 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
@@ -641,32 +640,52 @@ static int cgwb_create(struct backing_dev_info *bdi, 
 * each lookup.  On mismatch, the existing wb is discarded and a new one is

 * created.

 */

struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,

				    struct cgroup_subsys_state *memcg_css,

				    gfp_t gfp)

struct bdi_writeback *wb_get_lookup(struct backing_dev_info *bdi,

				    struct cgroup_subsys_state *memcg_css)

{

	struct bdi_writeback *wb;



	might_sleep_if(gfpflags_allow_blocking(gfp));



	if (!memcg_css->parent)

		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)))

		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)

{

	struct bdi_writeback *wb;



	might_sleep_if(gfpflags_allow_blocking(gfp));



	if (!memcg_css->parent)

		return &bdi->wb;



	do {

		wb = wb_get_lookup(bdi, memcg_css);

	} while (!wb && !cgwb_create(bdi, memcg_css, gfp));



	return wb;