Fix underflow in sizeBucketsPowerAndLocksPower()

Summary: If `cacheEntries` is too small, `bucketsPower_` will be less than 10. Since `bucketsPower_` is unsigned, it will underflow if we subtract 10 from it. Reviewed By: jaesoo-fb Differential Revision: D50994522 fbshipit-source-id: 55151fdab1982442a706267b3dd3a0bb6a6fd6e7
facebook · Nov 6, 2023 · 90d6313 · 90d6313
1 parent 0238600
commit 90d6313
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Showing 2 changed files with 6 additions and 1 deletion.
diff --git a/cachelib/allocator/ChainedHashTable.h b/cachelib/allocator/ChainedHashTable.h
@@ -286,7 +286,8 @@ class ChainedHashTable {
       }
 
       // 1 lock per 1000 buckets.
-      locksPower_ = std::max<unsigned int>(1, bucketsPower_ - 10);
+      locksPower_ =
+          (bucketsPower_ <= 20) ? (bucketsPower_ / 2) + 1 : bucketsPower_ - 10;
     }
 
     unsigned int getBucketsPower() const noexcept { return bucketsPower_; }

diff --git a/cachelib/allocator/tests/ChainedHashTest.cpp b/cachelib/allocator/tests/ChainedHashTest.cpp
@@ -33,6 +33,10 @@ TEST(ChainedHashTableConfigTest, Size) {
 
   ASSERT_THROW(config.sizeBucketsPowerAndLocksPower(2700000000),
                std::invalid_argument);
+
+  config.sizeBucketsPowerAndLocksPower(1);
+  EXPECT_EQ(config.getBucketsPower(), 1);
+  EXPECT_EQ(config.getLocksPower(), 1);
 }
 
 TEST_F(ChainedHashTest, Insert) { testInsert(); }