Date: Fri, 4 Mar 2011 14:17:44 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Dmitry Krivenok <krivenok.dmitry@gmail.com>, Andriy Gapon <avg@freebsd.org> Subject: Re: hw.physmem (loader.conf and sysctl) Message-ID: <201103041417.44584.jhb@freebsd.org> In-Reply-To: <4D712607.3090106@freebsd.org> References: <AANLkTi=QDBjw26fhZSRg6wrTB=E0-yEsWZuRK%2BZ7L03J@mail.gmail.com> <4D712607.3090106@freebsd.org>
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On Friday, March 04, 2011 12:48:55 pm Andriy Gapon wrote: > on 04/03/2011 16:36 Dmitry Krivenok said the following: > > Hello Hackers, > > I've limited the amount of physical memory visible for my FreeBSD-8.2 by adding > > the following in loader.conf: > > > > $ cat /boot/loader.conf | grep hw.physmem > > hw.physmem="500M" > > $ > > > > However, according to sysctl, the system sees > > > > $ sysctl hw.physmem > > hw.physmem: 507445248 > > $ > > > > The difference is (500 * 2**20 - 507445248) / 2**20 == 16.0625 Mb. > > How does the system use this "hidden" memory? > > Some memory is taken by structures that describe usable pages. > There is one vm_page_t structure per each 4KB page. > I believe that that memory is excluded from physmem. Also, the message buffer for dmesg, and the kernel binary itself. -- John Baldwin
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