[RFC PATCH] block: set bdi congested when no tag available

[Zhaoyang Huang <huangzhaoyang@xxxxxxxxx>]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

In previous version, block layer will set bdi to be congested when
get_request fail, which may throttle direct_reclaim. Move them back
under current blk-mq design.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 block/blk-mq-tag.c      | 18 +++++++++++++++++-
 include/linux/sbitmap.h |  1 +
 lib/sbitmap.c           | 17 +++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 995336a..bd1e520 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -11,6 +11,7 @@

 #include <linux/blk-mq.h>
 #include <linux/delay.h>
+#include <linux/backing-dev.h>
 #include "blk.h"
 #include "blk-mq.h"
 #include "blk-mq-sched.h"
@@ -126,8 +127,11 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
  if (tag != BLK_MQ_NO_TAG)
  goto found_tag;

- if (data->flags & BLK_MQ_REQ_NOWAIT)
+ if (data->flags & BLK_MQ_REQ_NOWAIT) {
+ set_bdi_congested(data->q->disk->bdi,BLK_RW_SYNC);
+ set_bdi_congested(data->q->disk->bdi,BLK_RW_ASYNC);
  return BLK_MQ_NO_TAG;
+ }

  ws = bt_wait_ptr(bt, data->hctx);
  do {
@@ -193,9 +197,21 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
  return tag + tag_offset;
 }

+static bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
+{
+ if (!tags)
+ return true;
+
+ return sbitmap_any_bit_clear(&tags->bitmap_tags.sb);
+}
+
 void blk_mq_put_tag(struct blk_mq_tags *tags, struct blk_mq_ctx *ctx,
      unsigned int tag)
 {
+ if (!blk_mq_has_free_tags(tags)) {
+ clear_bdi_congested(ctx->queue->disk->bdi, BLK_RW_SYNC);
+ clear_bdi_congested(ctx->queue->disk->bdi, BLK_RW_ASYNC);
+ }
  if (!blk_mq_tag_is_reserved(tags, tag)) {
  const int real_tag = tag - tags->nr_reserved_tags;

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 4a6ff27..30a5553 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -210,6 +210,7 @@ static inline void sbitmap_free(struct sbitmap *sb)
  * Return: true if any bit in the bitmap is set, false otherwise.
  */
 bool sbitmap_any_bit_set(const struct sbitmap *sb);
+bool sbitmap_any_bit_clear(const struct sbitmap *sb);

 #define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
 #define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 2709ab8..baa30d8 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -309,6 +309,23 @@ bool sbitmap_any_bit_set(const struct sbitmap *sb)
 }
 EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);

+bool sbitmap_any_bit_clear(const struct sbitmap *sb)
+{
+ unsigned int i;
+
+ for (i = 0; i < sb->map_nr; i++) {
+ const struct sbitmap_word *word = &sb->map[i];
+ unsigned long mask = word->word & ~word->cleared;
+ unsigned long ret;
+
+ ret = find_first_zero_bit(&mask, word->depth);
+ if (ret < word->depth)
+ return true;
+ }
+ return false;
+}
+EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
+
 static unsigned int __sbitmap_weight(const struct sbitmap *sb, bool set)
 {
  unsigned int i, weight = 0;
-- 
1.9.1