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SubjectRe: msync() behaviour broken for MS_ASYNC, revert patch?
Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> > It's a bit of a disaster if you happen to msync(MS_ASYNC) the same page at
> > any sort of frequency - we have to wait for the previous I/O to complete
> > before new I/O can be started. That was the main problem which caused this
> > change to be made. You can see that it'd make 100x or 1000x speed improvements
> > with some sane access patterns.
> >
>
> I'm not sure you'd have to do that, would you? Just move the dirty bit
> from the pte and skip the page if it is found locked or writeback.

That would make MS_ASYNC mean "start I/O now, unless there's I/O in
progress, in whch case start I/O in 30 seconds. That's not good.

If we're going to change the kernel, better off using fadvise()
enhancements, whic are also useful for post-write() operations.

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