[Python-Dev] obmalloc mmap/munmap thrashing

[Tim Peters]

You may be interested in this seemingly related bug report:

    http://bugs.python.org/issue26601

[Neil Schemenauer <neil at python.ca>]
> I was running Python 2.4.11 under strace and I noticed some odd
> looking system calls:
>
> mmap(NULL, 262144, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f9848681000
> munmap(0x7f9848681000, 262144)          = 0
> mmap(NULL, 262144, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f9848681000
> munmap(0x7f9848681000, 262144)          = 0
> [... repeated a number of times ...]
>
> Looking at obmalloc.c, there doesn't seem to be any high/low
> watermark (hysteresis) associated with unallocating arenas.  Is that
> true?  If so, does it seem prudent to implement something to avoid
> this behavior?  It seems potentially expensive if you program is
> running just at the threshold of needing another arena.