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Date: Fri, 19 Jan 2007 10:02:19 -0800
From: Paul Allen <nospam@ugcs.caltech.edu>
To: Jason Evans <jasone@freebsd.org>
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Cc: freebsd-current@freebsd.org, Stefan Ehmann <shoesoft@gmx.net>
Subject: Re: very high memory usage in -current
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>From Jason Evans <jasone@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