bdi: separate out congested state into a separate struct

Currently, a wb's (bdi_writeback) congestion state is carried in its
->state field; however, cgroup writeback support will require multiple
wb's sharing the same congestion state.  This patch separates out
congestion state into its own struct - struct bdi_writeback_congested.
A new field wb field, wb_congested, points to its associated congested
struct.  The default wb, bdi->wb, always points to bdi->wb_congested.

While this patch adds a layer of indirection, it doesn't introduce any
behavior changes.

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

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index aa18c4b..9e9eafa 100644 (file)
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -16,12 +16,15 @@ struct dentry;
  * Bits in bdi_writeback.state
  */
 enum wb_state {
-       WB_async_congested,     /* The async (write) queue is getting full */
-       WB_sync_congested,      /* The sync queue is getting full */
        WB_registered,          /* bdi_register() was done */
        WB_writeback_running,   /* Writeback is in progress */
 };
 
+enum wb_congested_state {
+       WB_async_congested,     /* The async (write) queue is getting full */
+       WB_sync_congested,      /* The sync queue is getting full */
+};
+
 typedef int (congested_fn)(void *, int);
 
 enum wb_stat_item {
@@ -34,6 +37,10 @@ enum wb_stat_item {
 
 #define WB_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
+struct bdi_writeback_congested {
+       unsigned long state;            /* WB_[a]sync_congested flags */
+};
+
 struct bdi_writeback {
        struct backing_dev_info *bdi;   /* our parent bdi */
 
@@ -48,6 +55,8 @@ struct bdi_writeback {
 
        struct percpu_counter stat[NR_WB_STAT_ITEMS];
 
+       struct bdi_writeback_congested *congested;
+
        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 */
@@ -84,6 +93,7 @@ struct backing_dev_info {
        unsigned int max_ratio, max_prop_frac;
 
        struct bdi_writeback wb;  /* default writeback info for this bdi */
+       struct bdi_writeback_congested wb_congested;
 
        struct device *dev;
 

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 7857820..bfdaa18 100644 (file)
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -167,7 +167,7 @@ static inline int bdi_congested(struct backing_dev_info *bdi, int bdi_bits)
 {
        if (bdi->congested_fn)
                return bdi->congested_fn(bdi->congested_data, bdi_bits);
-       return (bdi->wb.state & bdi_bits);
+       return (bdi->wb.congested->state & bdi_bits);
 }
 
 static inline int bdi_read_congested(struct backing_dev_info *bdi)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 805b287..5ec7658 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -383,6 +383,9 @@ int bdi_init(struct backing_dev_info *bdi)
        if (err)
                return err;
 
+       bdi->wb_congested.state = 0;
+       bdi->wb.congested = &bdi->wb_congested;
+
        return 0;
 }
 EXPORT_SYMBOL(bdi_init);
@@ -504,7 +507,7 @@ void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
        wait_queue_head_t *wqh = &congestion_wqh[sync];
 
        bit = sync ? WB_sync_congested : WB_async_congested;
-       if (test_and_clear_bit(bit, &bdi->wb.state))
+       if (test_and_clear_bit(bit, &bdi->wb.congested->state))
                atomic_dec(&nr_bdi_congested[sync]);
        smp_mb__after_atomic();
        if (waitqueue_active(wqh))
@@ -517,7 +520,7 @@ void set_bdi_congested(struct backing_dev_info *bdi, int sync)
        enum wb_state bit;
 
        bit = sync ? WB_sync_congested : WB_async_congested;
-       if (!test_and_set_bit(bit, &bdi->wb.state))
+       if (!test_and_set_bit(bit, &bdi->wb.congested->state))
                atomic_inc(&nr_bdi_congested[sync]);
 }
 EXPORT_SYMBOL(set_bdi_congested);