os/bluestore: do not assign already cached buffer to

mempool_bluestore_writing.

This spoils mempool stats with unexpectedly high mount of entries in
the bluestore_writing mempool.
The issue might occurs while handling partial overwrites in EC pools.
Unser some circumstances EC backend might rewrite data from read cache back to disk.

Signed-off-by: Igor Fedotov <[email protected]>

src/os/bluestore/BlueStore.h

@@ -297,11 +297,13 @@ class BlueStore : public ObjectStore,
       ceph_assert(writing.empty());
     }
 
-    void _add_buffer(BufferCacheShard* cache, Buffer *b, int level, Buffer *near) {
+    void _add_buffer(BufferCacheShard* cache, Buffer* b, int level, Buffer* near) {
       cache->_audit("_add_buffer start");
       buffer_map[b->offset].reset(b);
       if (b->is_writing()) {
-	b->data.reassign_to_mempool(mempool::mempool_bluestore_writing);
+        // we might get already cached data for which resetting mempool is inppropriate
+        // hence calling try_assign_to_mempool
+        b->data.try_assign_to_mempool(mempool::mempool_bluestore_writing);
         if (writing.empty() || writing.rbegin()->seq <= b->seq) {
           writing.push_back(*b);
         } else {
@@ -316,8 +318,8 @@ class BlueStore : public ObjectStore,
           writing.insert(it, *b);
         }
       } else {
-	b->data.reassign_to_mempool(mempool::mempool_bluestore_cache_data);
-	cache->_add(b, level, near);
+        b->data.reassign_to_mempool(mempool::mempool_bluestore_cache_data);
+        cache->_add(b, level, near);
       }
       cache->_audit("_add_buffer end");
     }