Date: Sun, 28 Jun 2009 20:54:19 -0400 From: Nathanael Hoyle <nhoyle@hoyletech.com> To: alc@freebsd.org Cc: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>, freebsd-hackers@freebsd.org Subject: Re: large pages (amd64) Message-ID: <4A4810BB.1010007@hoyletech.com> In-Reply-To: <ca3526250906281741h5c6c9407vdf9ea849330023ed@mail.gmail.com> References: <alpine.BSF.2.00.0906281933580.1809@wojtek.tensor.gdynia.pl> <4A480760.50705@hoyletech.com> <ca3526250906281741h5c6c9407vdf9ea849330023ed@mail.gmail.com>
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Alan Cox wrote: > On Sun, Jun 28, 2009 at 7:14 PM, Nathanael Hoyle <nhoyle@hoyletech.com>wrote: > > >> Wojciech Puchar 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 >>> >>> 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. >>> >>> certainly there are apps that could be put on big pages, gimp editing 40MB >>> bitmap for example >>> >>> >> Just to be clear, since you say i386 (I presume you mean architecture), I >> believe the Physical Address Extensions which allowed 2MB Page Size bit to >> be set was introduced with Pentium Pro. Processors prior to this were >> limited to standard 4KB pages. >> >> > > No. Many of those processors supported 4MB pages. > > Regards, > Alan > _______________________________________________ > Having been corrected by both you and Joerg (thank you!), I went back to re-verify my understanding. It appears that while I was slightly mixing PAE in with PSE, PSE support for 4MB pages was introduced 'silently' with the Pentium, and documented first with the Pentium Pro. I haven't found anything that points to earlier inclusion. Certainly the 80386 processor specifically, I am fairly confident would be limited to the 4KB pages. Agreed? Or are you aware of earlier usage than the Pentium for 4MB pages? Thanks, -Nathanael
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