Messages in this thread | | | Date | Tue, 1 Aug 2006 14:34:17 +0200 | From | "Antonio Vargas" <> | Subject | Re: [PATCH 1 of 13] Add apply_to_page_range() which applies a function to a pte range |
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On 8/1/06, Eric W. Biederman <ebiederm@xmission.com> wrote: > Jeremy Fitzhardinge <jeremy@xensource.com> writes: > > > 2 files changed, 99 insertions(+) > > include/linux/mm.h | 5 ++ > > mm/memory.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > > > > Add a new mm function apply_to_page_range() which applies a given > > function to every pte in a given virtual address range in a given mm > > structure. This is a generic alternative to cut-and-pasting the Linux > > idiomatic pagetable walking code in every place that a sequence of > > PTEs must be accessed. > > > > Although this interface is intended to be useful in a wide range of > > situations, it is currently used specifically by several Xen > > subsystems, for example: to ensure that pagetables have been allocated > > for a virtual address range, and to construct batched special > > pagetable update requests to map I/O memory (in ioremap()). > > - You don't handle huge pages. For a generic function > that sounds like a problem. > - I believe there is a reason the kernel doesn't already have > a function like this. I seem to recall there being efficiency > and fast path arguments.
The proper trick for this is:
1. place you "for each page" code in a #define like so:
#define FOR_EACH_PAGE_INNER do{ ... code ... }while(0);
2. create your function in a separate .h file without the double-include guard
3. inside this code, exchange the indirect function call with your define name:
(*fn)(args); --> FOR_EACH_PAGE_INNER
4. document how the macro will receive certain variables from it's outer scope, and should leave the "function result" in another one.
this in effect creates a different copy of the page walker for each function, and inlines your code in it.. just like it would do with a C++ template.
A place where you can see this technique working is the software triangle filler from MESA.
The doubt is... is this acceptable regarding linux-kernel coding-style?
> - Placing this code in mm/memory.c without a common consumer is > pure kernel bloat for everyone who doesn't use this function, > which is just about everyone. >
-- Greetz, Antonio Vargas aka winden of network
http://network.amigascne.org/ windNOenSPAMntw@gmail.com thesameasabove@amigascne.org
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