dm space map: optimise sm_ll_dec and sm_ll_inc

Prior to this patch these methods did a lookup followed by an insert.
Instead they now call a common mutate function that adjusts the value
according to a callback function.  This avoids traversing the data
structures twice and hence improves performance.

Also factor out sm_ll_lookup_big_ref_count() for use by both
sm_ll_lookup() and sm_ll_mutate().

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

1 files changed, 49 insertions, 28 deletions

diff --git a/drivers/md/persistent-data/dm-space-map-common.c b/drivers/md/persistent-data/dm-space-map-common.c
index 3e7a88d99eb0..6058569fe86c 100644
--- a/drivers/md/persistent-data/dm-space-map-common.c
+++ b/drivers/md/persistent-data/dm-space-map-common.c
@@ -292,16 +292,11 @@ int sm_ll_lookup_bitmap(struct ll_disk *ll, dm_block_t b, uint32_t *result)
         return dm_tm_unlock(ll->tm, blk);
 }
 
-int sm_ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result)
+static int sm_ll_lookup_big_ref_count(struct ll_disk *ll, dm_block_t b,
+                                      uint32_t *result)
 {
         __le32 le_rc;
-        int r = sm_ll_lookup_bitmap(ll, b, result);
-
-        if (r)
-                return r;
-
-        if (*result != 3)
-                return r;
+        int r;
 
         r = dm_btree_lookup(&ll->ref_count_info, ll->ref_count_root, &b, &le_rc);
         if (r < 0)
@@ -312,6 +307,19 @@ int sm_ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result)
         return r;
 }
 
+int sm_ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result)
+{
+        int r = sm_ll_lookup_bitmap(ll, b, result);
+
+        if (r)
+                return r;
+
+        if (*result != 3)
+                return r;
+
+        return sm_ll_lookup_big_ref_count(ll, b, result);
+}
+
 int sm_ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
                           dm_block_t end, dm_block_t *result)
 {
@@ -372,11 +380,12 @@ int sm_ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
         return -ENOSPC;
 }
 
-int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
-                 uint32_t ref_count, enum allocation_event *ev)
+static int sm_ll_mutate(struct ll_disk *ll, dm_block_t b,
+                        uint32_t (*mutator)(void *context, uint32_t old),
+                        void *context, enum allocation_event *ev)
 {
         int r;
-        uint32_t bit, old;
+        uint32_t bit, old, ref_count;
         struct dm_block *nb;
         dm_block_t index = b;
         struct disk_index_entry ie_disk;
@@ -399,6 +408,14 @@ int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
         bm_le = dm_bitmap_data(nb);
         old = sm_lookup_bitmap(bm_le, bit);
 
+        if (old > 2) {
+                r = sm_ll_lookup_big_ref_count(ll, b, &old);
+                if (r < 0)
+                        return r;
+        }
+
+        ref_count = mutator(context, old);
+
         if (ref_count <= 2) {
                 sm_set_bitmap(bm_le, bit, ref_count);
 
@@ -448,31 +465,35 @@ int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
         return ll->save_ie(ll, index, &ie_disk);
 }
 
-int sm_ll_inc(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
+static uint32_t set_ref_count(void *context, uint32_t old)
 {
-        int r;
-        uint32_t rc;
-
-        r = sm_ll_lookup(ll, b, &rc);
-        if (r)
-                return r;
+        return *((uint32_t *) context);
+}
 
-        return sm_ll_insert(ll, b, rc + 1, ev);
+int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
+                 uint32_t ref_count, enum allocation_event *ev)
+{
+        return sm_ll_mutate(ll, b, set_ref_count, &ref_count, ev);
 }
 
-int sm_ll_dec(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
+static uint32_t inc_ref_count(void *context, uint32_t old)
 {
-        int r;
-        uint32_t rc;
+        return old + 1;
+}
 
-        r = sm_ll_lookup(ll, b, &rc);
-        if (r)
-                return r;
+int sm_ll_inc(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
+{
+        return sm_ll_mutate(ll, b, inc_ref_count, NULL, ev);
+}
 
-        if (!rc)
-                return -EINVAL;
+static uint32_t dec_ref_count(void *context, uint32_t old)
+{
+        return old - 1;
+}
 
-        return sm_ll_insert(ll, b, rc - 1, ev);
+int sm_ll_dec(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
+{
+        return sm_ll_mutate(ll, b, dec_ref_count, NULL, ev);
 }
 
 int sm_ll_commit(struct ll_disk *ll)