return v;
}
- /* Round requested size. */
+ /*
+ * Round requested size.
+ *
+ * Step 1: round up to the minimum object size.
+ * Step 2: round up to a multiple of the user data size (e.g. 4)
+ * Step 3: if non-trivial alignment requested, round up
+ * so that the object precisely fills a chunk
+ * as big as the alignment request.
+ *
+ * Step 3 prevents the code from going into "bin search hyperspace":
+ * looking at a huge number of fractional remainder chunks, none of which
+ * will satisfy the alignment constraint. This fixes an allocator
+ * performance issue when one requests a large number of 16 byte objects
+ * aligned to 64 bytes, to name one variation on the theme.
+ */
n_user_data_bytes = clib_max (n_user_data_bytes, MHEAP_MIN_USER_DATA_BYTES);
n_user_data_bytes =
round_pow2 (n_user_data_bytes,
STRUCT_SIZE_OF (mheap_elt_t, user_data[0]));
-
+ if (align > MHEAP_ELT_OVERHEAD_BYTES)
+ n_user_data_bytes = clib_max (n_user_data_bytes,
+ align - MHEAP_ELT_OVERHEAD_BYTES);
if (!v)
v = mheap_alloc (0, 64 << 20);