Re: [Patch] shm bug introduced with pagecache in 2.3.11

Linus Torvalds (torvalds@transmeta.com)
Fri, 19 Nov 1999 11:25:45 -0800 (PST)


On Fri, 19 Nov 1999, Alan Cox wrote:
>
> News servers like Typhoon , high performance threaded web servers (eg Zeus)
>
> Fortunately these guys tend to be using pretty serious I/O subsystems not
> M/O disks and they are fine with 2.2.

Well, the more I look at a read-write semaphore, the more I like it: it
looks like something that once the semaphore implementation itself was
done, the MM side would be absolutely trivial. It does introduce a new
issue (multiple threads updating the page tables at the same time), but
that one doesn't look that horrible..

We don't ever export the page table handling to the low-level filesystems
any more (we used to a long time ago: the nopage() function got to touch
the page tables itself rather than just return the right page), so fixing
up the new issue is actually a very local fix in mm/mmeory.c.

Is anybody willing to take a stab at creating a read-write semaphore?

Linus

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