Messages in this thread | | | Date | Mon, 14 Jul 2008 08:39:55 +0200 | From | Andi Kleen <> | Subject | Re: [PATCh] x86: overmapped fix when 4K pages on tail - 64bit |
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H. Peter Anvin wrote: > Andi Kleen wrote: >> >> First I was only commenting on one specific patch, nothing more. >> >> My point is full rounding to 4K on all corners is wasteful because the >> CPUs have to handle that case anyways and every split costs precious >> TLB entries in direct mapping accesses. >> > > Well, the CPU *does* handle them... by splitting the larger pages into > smaller pages. They still end up in the small-page TLB, so there is no > real difference if done in the CPU or in software.
There's actually a difference in some cases, but that's a different issue.
Only when the hole is a real hole. But when it's just some firmware area or similar that's not needed.
> Memory state transitions are (fortunately) relatively rare and > long-lived,
That's not true today with several 3d driver setups. Also in general I would expect more PAT use in the future and that is usually a split.
-Andi
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