writeback: bdi_for_each_wb() iteration is memcg ID based not blkcg

wb's (bdi_writeback's) are currently keyed by memcg ID; however, in an
earlier implementation, wb's were keyed by blkcg ID.
bdi_for_each_wb() walks bdi->cgwb_tree in the ascending ID order and
allows iterations to start from an arbitrary ID which is used to
interrupt and resume iterations.

Unfortunately, while changing wb to be keyed by memcg ID instead of
blkcg, bdi_for_each_wb() was missed and is still assuming that wb's
are keyed by blkcg ID.  This doesn't affect iterations which don't get
interrupted but bdi_split_work_to_wbs() makes use of iteration
resuming on allocation failures and thus may incorrectly skip or
repeat wb's.

Fix it by changing bdi_for_each_wb() to take memcg IDs instead of
blkcg IDs and updating bdi_split_work_to_wbs() accordingly.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 518c6294bf6c0ef965e9f56baa4e11d2eccc0165..c9def2115aca99e47e45d079f0ba8606397c59ad 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -839,7 +839,7 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
                                  bool skip_if_busy)
 {
        long nr_pages = base_work->nr_pages;
-       int next_blkcg_id = 0;
+       int next_memcg_id = 0;
        struct bdi_writeback *wb;
        struct wb_iter iter;
 
@@ -849,14 +849,14 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
                return;
 restart:
        rcu_read_lock();
-       bdi_for_each_wb(wb, bdi, &iter, next_blkcg_id) {
+       bdi_for_each_wb(wb, bdi, &iter, next_memcg_id) {
                if (!wb_has_dirty_io(wb) ||
                    (skip_if_busy && writeback_in_progress(wb)))
                        continue;
 
                base_work->nr_pages = wb_split_bdi_pages(wb, nr_pages);
                if (!wb_clone_and_queue_work(wb, base_work)) {
-                       next_blkcg_id = wb->blkcg_css->id + 1;
+                       next_memcg_id = wb->memcg_css->id + 1;
                        rcu_read_unlock();
                        wb_wait_for_single_work(bdi, base_work);
                        goto restart;

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 0fe9df983ab7410c67143ecdc7a26bac958b4597..23ebb946e66fd6aeb9ca429e4812937026de223a 100644 (file)
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -402,7 +402,7 @@ static inline void unlocked_inode_to_wb_end(struct inode *inode, bool locked)
 }
 
 struct wb_iter {
-       int                     start_blkcg_id;
+       int                     start_memcg_id;
        struct radix_tree_iter  tree_iter;
        void                    **slot;
 };
@@ -414,9 +414,9 @@ static inline struct bdi_writeback *__wb_iter_next(struct wb_iter *iter,
 
        WARN_ON_ONCE(!rcu_read_lock_held());
 
-       if (iter->start_blkcg_id >= 0) {
-               iter->slot = radix_tree_iter_init(titer, iter->start_blkcg_id);
-               iter->start_blkcg_id = -1;
+       if (iter->start_memcg_id >= 0) {
+               iter->slot = radix_tree_iter_init(titer, iter->start_memcg_id);
+               iter->start_memcg_id = -1;
        } else {
                iter->slot = radix_tree_next_slot(iter->slot, titer, 0);
        }
@@ -430,30 +430,30 @@ static inline struct bdi_writeback *__wb_iter_next(struct wb_iter *iter,
 
 static inline struct bdi_writeback *__wb_iter_init(struct wb_iter *iter,
                                                   struct backing_dev_info *bdi,
-                                                  int start_blkcg_id)
+                                                  int start_memcg_id)
 {
-       iter->start_blkcg_id = start_blkcg_id;
+       iter->start_memcg_id = start_memcg_id;
 
-       if (start_blkcg_id)
+       if (start_memcg_id)
                return __wb_iter_next(iter, bdi);
        else
                return &bdi->wb;
 }
 
 /**
- * bdi_for_each_wb - walk all wb's of a bdi in ascending blkcg ID order
+ * bdi_for_each_wb - walk all wb's of a bdi in ascending memcg ID order
  * @wb_cur: cursor struct bdi_writeback pointer
  * @bdi: bdi to walk wb's of
  * @iter: pointer to struct wb_iter to be used as iteration buffer
- * @start_blkcg_id: blkcg ID to start iteration from
+ * @start_memcg_id: memcg ID to start iteration from
  *
  * Iterate @wb_cur through the wb's (bdi_writeback's) of @bdi in ascending
- * blkcg ID order starting from @start_blkcg_id.  @iter is struct wb_iter
+ * memcg ID order starting from @start_memcg_id.  @iter is struct wb_iter
  * to be used as temp storage during iteration.  rcu_read_lock() must be
  * held throughout iteration.
  */
-#define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id)             \
-       for ((wb_cur) = __wb_iter_init(iter, bdi, start_blkcg_id);      \
+#define bdi_for_each_wb(wb_cur, bdi, iter, start_memcg_id)             \
+       for ((wb_cur) = __wb_iter_init(iter, bdi, start_memcg_id);      \
             (wb_cur); (wb_cur) = __wb_iter_next(iter, bdi))
 
 #else  /* CONFIG_CGROUP_WRITEBACK */