Re: [patch] SMP alternatives

[Eric W. Biederman]

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.

Eric
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