os/bluestore: fix the allocate in bluefs

when bluefs succeed to reserve but failed to alloc in db space,

it will cause a assert, just because of the space fragmentation.

in this situation, it could not use slow device space,

and it would happen in stupid or avl allocator.

Signed-off-by: tangwenjun <tang.wenjun3@zte.com.cn>

src/os/bluestore/BlueFS.cc

@@ -1927,10 +1927,24 @@ int BlueFS::_allocate(uint8_t id, uint64_t len,
 
   uint64_t left = ROUND_UP_TO(len, min_alloc_size);
   int r = -ENOSPC;
+  int64_t alloc_len = 0;
+  AllocExtentVector extents;
+
   if (alloc[id]) {
     r = alloc[id]->reserve(left);
   }
-  if (r < 0) {
+
+  if (r == 0) {
+    uint64_t hint = 0;
+    if (!node->extents.empty() && node->extents.back().bdev == id) {
+      hint = node->extents.back().end();
+    }   
+    extents.reserve(4);  // 4 should be (more than) enough for most allocations
+    alloc_len = alloc[id]->allocate(left, min_alloc_size, hint, &extents);
+  }
+  if (r < 0 || (alloc_len < (int64_t)left)) {
+    if (r == 0)
+      alloc[id]->unreserve(left);
     if (id != BDEV_SLOW) {
       if (bdev[id]) {
 	dout(1) << __func__ << " failed to allocate 0x" << std::hex << left
@@ -1948,24 +1962,8 @@ int BlueFS::_allocate(uint8_t id, uint64_t len,
     else
       derr << __func__ << " failed to allocate 0x" << std::hex << left
 	   << " on bdev " << (int)id << ", dne" << std::dec << dendl;
-    return r;
-  }
-
-  uint64_t hint = 0;
-  if (!node->extents.empty() && node->extents.back().bdev == id) {
-    hint = node->extents.back().end();
-  }
-
-  AllocExtentVector extents;
-  extents.reserve(4);  // 4 should be (more than) enough for most allocations
-  int64_t alloc_len = alloc[id]->allocate(left, min_alloc_size, hint,
-                          &extents);
-  if (alloc_len < (int64_t)left) {
-    derr << __func__ << " allocate failed on 0x" << std::hex << left
-	 << " min_alloc_size 0x" << min_alloc_size 
-         << " hint 0x" <<  hint << std::dec << dendl;
-    alloc[id]->dump();
-    assert(0 == "allocate failed... wtf");
+    if (alloc[id]) 
+      alloc[id]->dump();    
     return -ENOSPC;
   }