[PATCH 20/49] bdi: separate out congested state into a separate struct

Tejun Heo
2015-04-06T20:00:05Z

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>
---
include/linux/backing-dev-defs.h | 14 ++++++++++++--
include/linux/backing-dev.h | 2 +-
mm/backing-dev.c | 7 +++++--
3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index aa18c4b..9e9eafa 100644
--- 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
--- 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
--- 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);
--
2.1.0