glibc malloc (ptmalloc2): The Big Picture

• Linux's default allocator is ptmalloc2, built into glibc. It hands out memory in units called chunks.
• Requests are rounded up and carry inline metadata: each chunk stores its own size and, when free, pointers to other free chunks.
• Freed chunks are not returned to the OS immediately; they are cached in bins (free lists) for fast reuse.
• The arena is the top-level bookkeeping structure that owns these bins. The main thread uses the main arena; extra threads get their own arenas.
• Design goal: speed. Reusing recently freed chunks is fast — but that reuse is exactly what attackers exploit.