Date: Sat, 9 Jun 2012 13:36:28 +0100 From: "Robert N. M. Watson" <rwatson@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Mikolaj Golub <trociny@freebsd.org>, Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>, Alan Cox <alc@freebsd.org>, Ivan Voras <ivoras@freebsd.org>, freebsd-hackers@freebsd.org Subject: Re: SuperPages utilization survey Message-ID: <32F2E0AA-B490-4ED3-988F-09226230652A@freebsd.org> In-Reply-To: <20120609100558.GM85127@deviant.kiev.zoral.com.ua> References: <jqac8f$6mn$1@dough.gmane.org> <alpine.BSF.2.00.1206011429160.20357@wojtek.tensor.gdynia.pl> <CAF-QHFXsi3SaF-rmFK-qM89LfnStKwRWN1-HRM4yg4Bt_SFAOg@mail.gmail.com> <86sje5kkl6.fsf@kopusha.home.net> <20120609083822.GJ85127@deviant.kiev.zoral.com.ua> <86obosluvk.fsf@kopusha.home.net> <20120609090740.GL85127@deviant.kiev.zoral.com.ua> <86k3zglsvm.fsf@kopusha.home.net> <20120609100558.GM85127@deviant.kiev.zoral.com.ua>
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On 9 Jun 2012, at 11:05, Konstantin Belousov wrote: > First, there is nothing which would prevent demotion from happens while > you iterate over the map, so you could get funyy numbers, like 42 superpages > for 2M region with your method. > > Second, the superpage size if machine-depended, and even single machine > could support differently sized superpage. For amd64, hardware can support > 2M and 1G pages, and for i386 you can get 4M or 2M depending on PAE config. > > And last, I in fact do not see much use for any 'superpage count'. Would I > would like to see is the TLB miss count for a region. Then I could estimate > whether superpage enabling provided some advantage. Just as a note, if > there were no accesses to a region after promotion, then promotion is > the waste. > > Anyway, please do not consider this as discouraging you from doing a > useful work. Despite the rendering and underlying semantic issues, I admit that I would like to know when superpages are being used by processes -- perhaps enough information to construct a histogram of page sizes for each mapping. Robert
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