Re: 2.4.0-test10-pre3:Oops in mm/filemap.c:filemap_write_pa

[Trond Myklebust]

>>>>> " " == Linus Torvalds <[EMAIL PROTECTED]> 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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