Date: Sun, 28 Jun 2009 16:51:17 -0500 From: Alan Cox <alan.l.cox@gmail.com> To: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> Cc: freebsd-hackers@freebsd.org Subject: Re: large pages (amd64) Message-ID: <ca3526250906281451g4441441bt3718d37dd848590a@mail.gmail.com> In-Reply-To: <alpine.BSF.2.00.0906281933580.1809@wojtek.tensor.gdynia.pl> References: <alpine.BSF.2.00.0906281933580.1809@wojtek.tensor.gdynia.pl>
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On Sun, Jun 28, 2009 at 12:36 PM, Wojciech Puchar < wojtek@wojtek.tensor.gdynia.pl> wrote: > i enabled > vm.pmap.pg_ps_enabled: 1 > > > could you please explain what exactly this values means? > because i don't understand why promotions-demotions!=mappings > "mappings" is not what you seem to think it is. vm.pmap.pde.mappings is the number of 2/4MB page mappings that are created directly and not through the incremental promotion process. For example, it counts the 2/4MB page mappings that are created when the text segment of a large executable, e.g., gcc, is pre-faulted at startup or when a graphics card's frame buffer is mmap()ed. Moreover, not every promoted mapping is demoted. A promoted mapping may be destroyed without demotion, for example, when a process exits. This is, in fact, the ideal case because it is cheaper to destroy a single 2/4MB page mapping instead of 512 or 1024 4KB page mappings. > > vm.pmap.pde.promotions: 2703 > vm.pmap.pde.p_failures: 6290 > vm.pmap.pde.mappings: 610 > vm.pmap.pde.demotions: 289 > > > > > other question - tried enabling it on my i386 laptop (256 megs ram), always > mappings==0, while promitions>demotions>0. > The default starting address for executables on i386 is not aligned to a 2/4MB page boundary. Hence, "mappings" are much less likely to occur. > certainly there are apps that could be put on big pages, gimp editing 40MB > bitmap for example Regards, Alan <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers><freebsd-hackers-unsubscribe@freebsd.org>;
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