Date: Tue, 02 Dec 2008 13:42:20 +0200 From: Giorgos Keramidas <keramida@freebsd.org> To: yuri@rawbw.com Cc: freebsd-questions@freebsd.org Subject: Re: Why process memory starts so high up in virtual space with FreeBSD malloc? Message-ID: <87ljuy2483.fsf@kobe.laptop> In-Reply-To: <49346BD3.5080506@rawbw.com> (yuri@rawbw.com's message of "Mon, 01 Dec 2008 14:57:23 -0800") References: <49345710.9070403@rawbw.com> <874p1njz3l.fsf@kobe.laptop> <49346BD3.5080506@rawbw.com>
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On Mon, 01 Dec 2008 14:57:23 -0800, Yuri <yuri@rawbw.com> wrote: > Giorgos Keramidas wrote: >> The FreeBSD malloc(3) implementation can use either mmap() or sbrk() to >> obtain memory from the system. It does not 'waste a high percentage of >> memory' but it simply maps only high addresses (with an unmapped 'hole' >> in lower addresses). > > But the hole it leaves with MALLOC_OPTIONS='dM' is way larger than the > one left by 'Dm' option. Usually malloc will keep allocating addresses > higher than this initial value and will never come back and fill some > parts of this gap. Therefore "wasting" this space. The 'D' and 'M' options set what malloc() will _prefer_, they do not force malloc() to use _only_ the particular type of memory space. As Dan explained in another post, both memory types will be used if there is need for more address space.
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