very high memory usage in -current

[Paul Allen]

>From Jason Evans <jasone at freebsd.org>, Thu, Jan 18, 2007 at 04:08:21PM -0800:
> Personally, in the absence of a dynamic boundary between the data
> segment and the heap, I would be quite happy to completely disable
> sbrk() support in jemalloc, and let those who really need that last 512
> MB of address space adjust resource limits for their applications as
> necessary.  In practice, I expect this would cause people far less
> trouble than does the current state of affairs.
Well it might be reasonable to use a malloc flag.  Nonetheless, it should
be possible for you to MADV_FREE brk memory without moving the brk point.
While munmap has some advantages in better coexisting with direct use of
mmap by a program, MADV_FREE has the advantage that virtual pages can be
immediately reused without incurring a syscall cost.  It isn't obvious
a priori what the right balance of these operations is.


                                    Paul