>>>>> " " == Linus Torvalds <torvalds@transmeta.com> writes:
> which is really really bad, because now you have the case that
> you have 'n' copies of the same page in memory, with 'n' users,
> out of which 'n-1' users have the wrong page. And those 'n-1'
> users don't even have any way of _knowing_ that they have the
> wrong page.
> Which is why we MUST NOT drop a page that has users. Really.
> I'm telling you that cases #4 and #5 are _much_ worse than your
> "solution" to case #2. And you argue that your solution is good
> only because you're completely ignoring cases #4 and #5.
No. I'm arguing (at 4:40am and while trying to keep one eye on our
detector's data acquisition) on the basis that whoever holds the file
lock has to have a guarantee of obtaining 100% accuracy on the locked
region.
I agree that dropping pages is ugly and that it will always give
problems with shared mmap(), so if it can be shown that clearing
PG_uptodate and rereading the same page will give the required
guarantee on locking, then I'm not going to complain.
Cheers,
Trond
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