Possible memory leak in Arena code

[GoogleCodeExporter]

I think there's a memory leak in the Arena code.

Consider a scenario where:
* You create and release 3 arenas, each with a chunk of say 20KB of memory.
* You create a new arena, using one of those chunks; there are 2 chunks
left on the free list.
* You attempt to allocate a chunk of size 100KB.

If I read the code correctly, the loop in Arena_alloc() - p94 of the third
printing - invokes <get a new chunk 95>. Each time that is called, it
removes a chunk from the freelist, finds that it is not big enough, and
discards it, rather than restoring it to the freelist or releasing it.
-- 
Jonathan Leffler <jonathan.leffler@gmail.com> 

Original issue reported on code.google.com by drhan...@gmail.com on 29 Sep 2008 at 7:50

[GoogleCodeExporter]

I don't think there's a memory leak, but the code that allocates new chunks, 
<get a
new check 95>, could certainly be improved.

The new check obtained in <ptr <- a new chunk 96>, whether allocated or taken 
from
the free list, becomes the first chunk on the arena's list of chunks by virtue 
of the
last 4 lines in <get a new chunk 95>.

Of course, *none* of this new chunk will be used when it's smaller than the
allocation request. Indeed, if the free list contains only chunks that are too 
small,
*all* of them will be moved to the arena's list of chunks and none of them will 
be
used! They will, however, be reclaimed when the arena is freed.

But it's obviously a waste to tie up chunks that aren't used. A better approach 
would
be to search the free list for a chunk that *can* satisfy the allocation 
request.

Original comment by drhan...@gmail.com on 29 Sep 2008 at 7:58