writeback: move backing_dev_info->bdi_stat[] into bdi_writeback

Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
and the role of the separation is unclear.  For cgroup support for
writeback IOs, a bdi will be updated to host multiple wb's where each
wb serves writeback IOs of a different cgroup on the bdi.  To achieve
that, a wb should carry all states necessary for servicing writeback
IOs for a cgroup independently.

This patch moves bdi->bdi_stat[] into wb.

* enum bdi_stat_item is renamed to wb_stat_item and the prefix of all
  enums is changed from BDI_ to WB_.

* BDI_STAT_BATCH() -> WB_STAT_BATCH()

* [__]{add|inc|dec|sum}_wb_stat(bdi, ...) -> [__]{add|inc}_wb_stat(wb, ...)

* bdi_stat[_error]() -> wb_stat[_error]()

* bdi_writeout_inc() -> wb_writeout_inc()

* stat init is moved to bdi_wb_init() and bdi_wb_exit() is added and
  frees stat.

* As there's still only one bdi_writeback per backing_dev_info, all
  uses of bdi->stat[] are mechanically replaced with bdi->wb.stat[]
  introducing no behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 32 insertions, 36 deletions

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index eb14f988a63e..fe7a907a4e16 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -36,15 +36,15 @@ enum wb_state {
 
 typedef int (congested_fn)(void *, int);
 
-enum bdi_stat_item {
-        BDI_RECLAIMABLE,
-        BDI_WRITEBACK,
-        BDI_DIRTIED,
-        BDI_WRITTEN,
-        NR_BDI_STAT_ITEMS
+enum wb_stat_item {
+        WB_RECLAIMABLE,
+        WB_WRITEBACK,
+        WB_DIRTIED,
+        WB_WRITTEN,
+        NR_WB_STAT_ITEMS
 };
 
-#define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
+#define WB_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
 struct bdi_writeback {
         struct backing_dev_info *bdi;   /* our parent bdi */
@@ -58,6 +58,8 @@ struct bdi_writeback {
         struct list_head b_more_io;     /* parked for more writeback */
         struct list_head b_dirty_time;  /* time stamps are dirty */
         spinlock_t list_lock;           /* protects the b_* lists */
+
+        struct percpu_counter stat[NR_WB_STAT_ITEMS];
 };
 
 struct backing_dev_info {
@@ -69,8 +71,6 @@ struct backing_dev_info {
 
         char *name;
 
-        struct percpu_counter bdi_stat[NR_BDI_STAT_ITEMS];
-
         unsigned long bw_time_stamp;    /* last time write bw is updated */
         unsigned long dirtied_stamp;
         unsigned long written_stamp;    /* pages written at bw_time_stamp */
@@ -137,78 +137,74 @@ static inline int wb_has_dirty_io(struct bdi_writeback *wb)
                !list_empty(&wb->b_more_io);
 }
 
-static inline void __add_bdi_stat(struct backing_dev_info *bdi,
-                enum bdi_stat_item item, s64 amount)
+static inline void __add_wb_stat(struct bdi_writeback *wb,
+                                 enum wb_stat_item item, s64 amount)
 {
-        __percpu_counter_add(&bdi->bdi_stat[item], amount, BDI_STAT_BATCH);
+        __percpu_counter_add(&wb->stat[item], amount, WB_STAT_BATCH);
 }
 
-static inline void __inc_bdi_stat(struct backing_dev_info *bdi,
-                enum bdi_stat_item item)
+static inline void __inc_wb_stat(struct bdi_writeback *wb,
+                                 enum wb_stat_item item)
 {
-        __add_bdi_stat(bdi, item, 1);
+        __add_wb_stat(wb, item, 1);
 }
 
-static inline void inc_bdi_stat(struct backing_dev_info *bdi,
-                enum bdi_stat_item item)
+static inline void inc_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
 {
         unsigned long flags;
 
         local_irq_save(flags);
-        __inc_bdi_stat(bdi, item);
+        __inc_wb_stat(wb, item);
         local_irq_restore(flags);
 }
 
-static inline void __dec_bdi_stat(struct backing_dev_info *bdi,
-                enum bdi_stat_item item)
+static inline void __dec_wb_stat(struct bdi_writeback *wb,
+                                 enum wb_stat_item item)
 {
-        __add_bdi_stat(bdi, item, -1);
+        __add_wb_stat(wb, item, -1);
 }
 
-static inline void dec_bdi_stat(struct backing_dev_info *bdi,
-                enum bdi_stat_item item)
+static inline void dec_wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
 {
         unsigned long flags;
 
         local_irq_save(flags);
-        __dec_bdi_stat(bdi, item);
+        __dec_wb_stat(wb, item);
         local_irq_restore(flags);
 }
 
-static inline s64 bdi_stat(struct backing_dev_info *bdi,
-                enum bdi_stat_item item)
+static inline s64 wb_stat(struct bdi_writeback *wb, enum wb_stat_item item)
 {
-        return percpu_counter_read_positive(&bdi->bdi_stat[item]);
+        return percpu_counter_read_positive(&wb->stat[item]);
 }
 
-static inline s64 __bdi_stat_sum(struct backing_dev_info *bdi,
-                enum bdi_stat_item item)
+static inline s64 __wb_stat_sum(struct bdi_writeback *wb,
+                                enum wb_stat_item item)
 {
-        return percpu_counter_sum_positive(&bdi->bdi_stat[item]);
+        return percpu_counter_sum_positive(&wb->stat[item]);
 }
 
-static inline s64 bdi_stat_sum(struct backing_dev_info *bdi,
-                enum bdi_stat_item item)
+static inline s64 wb_stat_sum(struct bdi_writeback *wb, enum wb_stat_item item)
 {
         s64 sum;
         unsigned long flags;
 
         local_irq_save(flags);
-        sum = __bdi_stat_sum(bdi, item);
+        sum = __wb_stat_sum(wb, item);
         local_irq_restore(flags);
 
         return sum;
 }
 
-extern void bdi_writeout_inc(struct backing_dev_info *bdi);
+extern void wb_writeout_inc(struct bdi_writeback *wb);
 
 /*
  * maximal error of a stat counter.
  */
-static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi)
+static inline unsigned long wb_stat_error(struct bdi_writeback *wb)
 {
 #ifdef CONFIG_SMP
-        return nr_cpu_ids * BDI_STAT_BATCH;
+        return nr_cpu_ids * WB_STAT_BATCH;
 #else
         return 1;
 #endif