Date: Fri, 04 Mar 2011 19:48:55 +0200 From: Andriy Gapon <avg@freebsd.org> To: Dmitry Krivenok <krivenok.dmitry@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: hw.physmem (loader.conf and sysctl) Message-ID: <4D712607.3090106@freebsd.org> In-Reply-To: <AANLkTi=QDBjw26fhZSRg6wrTB=E0-yEsWZuRK%2BZ7L03J@mail.gmail.com> References: <AANLkTi=QDBjw26fhZSRg6wrTB=E0-yEsWZuRK%2BZ7L03J@mail.gmail.com>
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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. -- Andriy Gapon
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