diff options
| -rw-r--r-- | malloc/malloc.c | 23 |
1 files changed, 15 insertions, 8 deletions
diff --git a/malloc/malloc.c b/malloc/malloc.c index b8c0f4f580..e2f1a615a4 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -3417,16 +3417,23 @@ __libc_realloc (void *oldmem, size_t bytes) if (__glibc_unlikely (mtag_enabled)) *(volatile char*) oldmem; - /* Return the chunk as is whenever possible, i.e. there's enough usable space - but not so much that we end up fragmenting the block. We use the trim - threshold as the heuristic to decide the latter. */ - size_t usable = musable (oldmem); - if (bytes <= usable - && (unsigned long) (usable - bytes) <= mp_.trim_threshold) - return oldmem; - /* chunk corresponding to oldmem */ const mchunkptr oldp = mem2chunk (oldmem); + + /* Return the chunk as is if the request grows within usable bytes, typically + into the alignment padding. We want to avoid reusing the block for + shrinkages because it ends up unnecessarily fragmenting the address space. + This is also why the heuristic misses alignment padding for THP for + now. */ + size_t usable = musable (oldmem); + if (bytes <= usable) + { + size_t difference = usable - bytes; + if ((unsigned long) difference < 2 * sizeof (INTERNAL_SIZE_T) + || (chunk_is_mmapped (oldp) && difference <= GLRO (dl_pagesize))) + return oldmem; + } + /* its size */ const INTERNAL_SIZE_T oldsize = chunksize (oldp); |