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, 37 insertions, 23 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index b23cf0ea5912..7b1d1917b658 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -84,13 +84,13 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
                    "b_dirty_time:       %10lu\n"
                    "bdi_list:           %10u\n"
                    "state:              %10lx\n",
-                   (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
-                   (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
+                   (unsigned long) K(wb_stat(wb, WB_WRITEBACK)),
+                   (unsigned long) K(wb_stat(wb, WB_RECLAIMABLE)),
                    K(bdi_thresh),
                    K(dirty_thresh),
                    K(background_thresh),
-                   (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
-                   (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
+                   (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
+                   (unsigned long) K(wb_stat(wb, WB_WRITTEN)),
                    (unsigned long) K(bdi->write_bandwidth),
                    nr_dirty,
                    nr_io,
@@ -376,8 +376,10 @@ void bdi_unregister(struct backing_dev_info *bdi)
 }
 EXPORT_SYMBOL(bdi_unregister);
 
-static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
+static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 {
+        int i, err;
+
         memset(wb, 0, sizeof(*wb));
 
         wb->bdi = bdi;
@@ -388,6 +390,27 @@ static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
         INIT_LIST_HEAD(&wb->b_dirty_time);
         spin_lock_init(&wb->list_lock);
         INIT_DELAYED_WORK(&wb->dwork, bdi_writeback_workfn);
+
+        for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
+                err = percpu_counter_init(&wb->stat[i], 0, GFP_KERNEL);
+                if (err) {
+                        while (--i)
+                                percpu_counter_destroy(&wb->stat[i]);
+                        return err;
+                }
+        }
+
+        return 0;
+}
+
+static void bdi_wb_exit(struct bdi_writeback *wb)
+{
+        int i;
+
+        WARN_ON(delayed_work_pending(&wb->dwork));
+
+        for (i = 0; i < NR_WB_STAT_ITEMS; i++)
+                percpu_counter_destroy(&wb->stat[i]);
 }
 
 /*
@@ -397,7 +420,7 @@ static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 
 int bdi_init(struct backing_dev_info *bdi)
 {
-        int i, err;
+        int err;
 
         bdi->dev = NULL;
 
@@ -408,13 +431,9 @@ int bdi_init(struct backing_dev_info *bdi)
         INIT_LIST_HEAD(&bdi->bdi_list);
         INIT_LIST_HEAD(&bdi->work_list);
 
-        bdi_wb_init(&bdi->wb, bdi);
-
-        for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
-                err = percpu_counter_init(&bdi->bdi_stat[i], 0, GFP_KERNEL);
-                if (err)
-                        goto err;
-        }
+        err = bdi_wb_init(&bdi->wb, bdi);
+        if (err)
+                return err;
 
         bdi->dirty_exceeded = 0;
 
@@ -427,25 +446,20 @@ int bdi_init(struct backing_dev_info *bdi)
         bdi->avg_write_bandwidth = INIT_BW;
 
         err = fprop_local_init_percpu(&bdi->completions, GFP_KERNEL);
-
         if (err) {
-err:
-                while (i--)
-                        percpu_counter_destroy(&bdi->bdi_stat[i]);
+                bdi_wb_exit(&bdi->wb);
+                return err;
         }
 
-        return err;
+        return 0;
 }
 EXPORT_SYMBOL(bdi_init);
 
 void bdi_destroy(struct backing_dev_info *bdi)
 {
-        int i;
-
         bdi_wb_shutdown(bdi);
 
         WARN_ON(!list_empty(&bdi->work_list));
-        WARN_ON(delayed_work_pending(&bdi->wb.dwork));
 
         if (bdi->dev) {
                 bdi_debug_unregister(bdi);
@@ -453,8 +467,8 @@ void bdi_destroy(struct backing_dev_info *bdi)
                 bdi->dev = NULL;
         }
 
-        for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
-                percpu_counter_destroy(&bdi->bdi_stat[i]);
+        bdi_wb_exit(&bdi->wb);
+
         fprop_local_destroy_percpu(&bdi->completions);
 }
 EXPORT_SYMBOL(bdi_destroy);