writeback: implement bdi_for_each_wb()

This will be used to implement bdi-wide operations which should be
distributed across all its cgroup bdi_writebacks.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 0839e44..c797980 100644 (file)
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -383,6 +383,61 @@ static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
        return inode->i_wb;
 }
 
+struct wb_iter {
+       int                     start_blkcg_id;
+       struct radix_tree_iter  tree_iter;
+       void                    **slot;
+};
+
+static inline struct bdi_writeback *__wb_iter_next(struct wb_iter *iter,
+                                                  struct backing_dev_info *bdi)
+{
+       struct radix_tree_iter *titer = &iter->tree_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;
+       } else {
+               iter->slot = radix_tree_next_slot(iter->slot, titer, 0);
+       }
+
+       if (!iter->slot)
+               iter->slot = radix_tree_next_chunk(&bdi->cgwb_tree, titer, 0);
+       if (iter->slot)
+               return *iter->slot;
+       return NULL;
+}
+
+static inline struct bdi_writeback *__wb_iter_init(struct wb_iter *iter,
+                                                  struct backing_dev_info *bdi,
+                                                  int start_blkcg_id)
+{
+       iter->start_blkcg_id = start_blkcg_id;
+
+       if (start_blkcg_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
+ * @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
+ *
+ * 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
+ * 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);      \
+            (wb_cur); (wb_cur) = __wb_iter_next(iter, bdi))
+
 #else  /* CONFIG_CGROUP_WRITEBACK */
 
 static inline bool inode_cgwb_enabled(struct inode *inode)
@@ -445,6 +500,14 @@ static inline void wb_blkcg_offline(struct blkcg *blkcg)
 {
 }
 
+struct wb_iter {
+       int             next_id;
+};
+
+#define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id)             \
+       for ((iter)->next_id = (start_blkcg_id);                        \
+            ({ (wb_cur) = !(iter)->next_id++ ? &(bdi)->wb : NULL; }); )
+
 static inline int inode_congested(struct inode *inode, int cong_bits)
 {
        return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);