Re: [patch] SMP alternatives

From: Eric W. Biederman
Date: Wed Nov 23 2005 - 18:31:04 EST

Linus Torvalds <torvalds@xxxxxxxx> writes:

> On Wed, 23 Nov 2005, H. Peter Anvin wrote:
>> Yes. Any shared mmaps may require working lock.
> Not "any". Only writable shared mmap. Which is actually the rare case.
> Even then, we might want to have such processes have a way to say "I don't
> do futexes in this mmap" or similar. Quite often, writable shared mmaps
> aren't interested in locked cycles - they are there to just write things
> to disk, and all the serialization is done in the kernel when the user
> does a "munmap()" or a "msync()".

In fact for being explict we already have PROT_SEM on some architectures
to report if we are going to use atomic operations, in the mmap. For
x86 we would probably need to introduce a PROT_NOSEM but it is sounds
fairly straight forward to implement.

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