realloc에 대해서..

저도 malloc의 동작을 좀 분석하기 위해서 소스를 최근에 봤는데
realloc 알고리즘이 이렇다는 군요 ^^;

제 glibc 버젼은 glibc-2.1.3-15 입니다.

/*

Realloc algorithm:

Chunks that were obtained via mmap cannot be extended or shrunk
unless HAVE_MREMAP is defined, in which case mremap is used.
Otherwise, if their reallocation is for additional space, they are
copied. If for less, they are just left alone.

Otherwise, if the reallocation is for additional space, and the
chunk can be extended, it is, else a malloc-copy-free sequence is
taken. There are several different ways that a chunk could be
extended. All are tried:

* Extending forward into following adjacent free chunk.
* Shifting backwards, joining preceding adjacent space
* Both shifting backwards and extending forward.
* Extending into newly sbrked space

Unless the #define REALLOC_ZERO_BYTES_FREES is set, realloc with a
size argument of zero (re)allocates a minimum-sized chunk.

If the reallocation is for less space, and the new request is for
a `small' (<512 bytes) size, then the newly unused space is lopped
off and freed.

The old unix realloc convention of allowing the last-free'd chunk
to be used as an argument to realloc is no longer supported.
I don't know of any programs still relying on this feature,
and allowing it would also allow too many other incorrect
usages of realloc to be sensible.

*/

참고
ftp://g.oswego.edu/pub/misc/malloc.c
http://g.oswego.edu/dl/html/malloc.html
http://www.ezdoum.com/search.php?query=malloc