Messages in this thread | | | Date | Thu, 2 May 2002 15:34:02 +0200 | From | Andrea Arcangeli <> | Subject | Re: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?] |
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On Wed, May 01, 2002 at 04:41:17AM +0200, Daniel Phillips wrote: > On Thursday 02 May 2002 03:43, Andrea Arcangeli wrote: > > On Wed, May 01, 2002 at 03:26:22AM +0200, Daniel Phillips wrote: > > > For your information, the mem_map lives in *virtual* memory, it does not > > > need to change location, only the kernel page tables need to be updated, > > > to allow a section of kernel memory to be moved to a different physical > > > location. For user memory, this was always possible, now it is possible > > > for kernel memory as well. Naturally, it's not all you have to do to get > > > hotplug memory, but it's a big step in that direction. > > > > what kernel pagetables? > > The normal page tables that are used to map kernel memory. > > > pagetables for space that you left free for what? > > These page tables have not been left free for anything. The nice thing about > page tables is that you can change the page table entries to point wherever > you want. (I know you know this.) This is what config_nonlinear supports, > and that is why it's called config_nonlinear. When we want to remap part of > the kernel memory to a different piece of physical memory, we just need to > fill in some pte's. The tricky part is knowing how to fill in the ptes, and > config_nonlinear takes care of that. > > > You waste virtual space for that at the very least on x86 that is > > just very tigh, at this point kernel virtual space is more costly than > > physical space these days. And nevertheless most archs doesn't have > > pagetables at all to read and write the page structures. yes it's > > virtual memory but it's a direct mapping. > > Most architectures? That's quite possibly an exaggeration. Some > architectures - MIPS32 for example - make this difficult or impossible, > and so what? Those can't do software hotplug memory, sorry.
alpha is the same as mips I think. sparc would be the same too if there's any discontigmem sparc. Dunno of arm. We're talking about architectures needing discontigmem, 99% percent of users doesn't need discontigmem in the first place, you never need discontigmem in x86 and even in new-numa you don't need discontigmem, you want to pass through discontigmem only to get the numa topology description that the current discontigmem provides via the pgdat.
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