dm bitset: only flush the current word if it has been dirtied

This change offers a big performance boost for dm-era.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

2 files changed, 10 insertions, 1 deletions

diff --git a/drivers/md/persistent-data/dm-bitset.c b/drivers/md/persistent-data/dm-bitset.c
index cd9a86d4cdf0..36f7cc2c7109 100644
--- a/drivers/md/persistent-data/dm-bitset.c
+++ b/drivers/md/persistent-data/dm-bitset.c
@@ -65,7 +65,7 @@ int dm_bitset_flush(struct dm_disk_bitset *info, dm_block_t root,
         int r;
         __le64 value;
 
-        if (!info->current_index_set)
+        if (!info->current_index_set || !info->dirty)
                 return 0;
 
         value = cpu_to_le64(info->current_bits);
@@ -77,6 +77,8 @@ int dm_bitset_flush(struct dm_disk_bitset *info, dm_block_t root,
                 return r;
 
         info->current_index_set = false;
+        info->dirty = false;
+
         return 0;
 }
 EXPORT_SYMBOL_GPL(dm_bitset_flush);
@@ -94,6 +96,8 @@ static int read_bits(struct dm_disk_bitset *info, dm_block_t root,
         info->current_bits = le64_to_cpu(value);
         info->current_index_set = true;
         info->current_index = array_index;
+        info->dirty = false;
+
         return 0;
 }
 
@@ -126,6 +130,8 @@ int dm_bitset_set_bit(struct dm_disk_bitset *info, dm_block_t root,
                 return r;
 
         set_bit(b, (unsigned long *) &info->current_bits);
+        info->dirty = true;
+
         return 0;
 }
 EXPORT_SYMBOL_GPL(dm_bitset_set_bit);
@@ -141,6 +147,8 @@ int dm_bitset_clear_bit(struct dm_disk_bitset *info, dm_block_t root,
                 return r;
 
         clear_bit(b, (unsigned long *) &info->current_bits);
+        info->dirty = true;
+
         return 0;
 }
 EXPORT_SYMBOL_GPL(dm_bitset_clear_bit);
diff --git a/drivers/md/persistent-data/dm-bitset.h b/drivers/md/persistent-data/dm-bitset.h
index e1b9bea14aa1..c2287d672ef5 100644
--- a/drivers/md/persistent-data/dm-bitset.h
+++ b/drivers/md/persistent-data/dm-bitset.h
@@ -71,6 +71,7 @@ struct dm_disk_bitset {
         uint64_t current_bits;
 
         bool current_index_set:1;
+        bool dirty:1;
 };
 
 /*