Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: [PATCH] fix remap of shared read only mappings | Date | Fri, 5 Sep 2003 03:31:38 +0200 |
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On Friday 05 September 2003 03:07, Alan Cox wrote: > On Gwe, 2003-09-05 at 01:49, Linus Torvalds wrote: > > What really matters is that mmap() under Linux is 100% coherent, as far > > as the hardware just allows. We haven't taken the easy way out. We > > shouldn't start now. > > NFS ?
NFS doesn't attempt to implement local Posix semantics, but a DFS should. Anyway, Linus has ruled we're being held to the higher standard of "Linux semantics".
> The problem with OpenGFS is that it is a network file system so > implementing "perfect" shared mmap semantics might actually reduce it > from handy to useless. Right now the worst we have to do is mark pages > uncached in some weird shared map cases, with pages being bounced across > firewire its a bit different.
Sistina has been doing it the "perfect" way for some time now, and it's worked out OK. This relies on writes being rare.
Things will definitely slow to a crawl if several nodes keep writing little bits into the same mmap, but that's a case of "doctor it hurts" I think. If there's a common application that does this, I'd appreciate knowing about it.
Regards,
Daniel
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