On Tue, 12 Sep 2000, Chris Mason wrote:
> --On 09/12/00 10:30:28 -0400 Alexander Viro <[EMAIL PROTECTED]> wrote:
>
> >
> >
> > On Tue, 12 Sep 2000, Chris Mason wrote:
> >
> >> Almost, truncate could remove the file items in the middle of the
> >> unmerge.
> >>
> >> proc1: writepage->prepare_write->unmerge
> >
> > Chris, RTFPOSIX. pageout should _never_ expand the file. _If_ you are
> > using ->prepare_write() in ->writepage() at all (you don't have to) it
> > should go only up to ->i_size, or you've got much more serious problems.
> >
> > IOW, ->writepage() has no business unmerging anything.
> >
>
> Yes, another option is to have writepage go directly into the tail (as said
> in the other posts). With or without the unmerge, it is still a
> concurrency issue, the point was the tail can go away in the middle of a
> writepage.
Check vmtruncate(). It will start with setting ->i_size and that should
stop any new attemtps of writepage(). Then it will acquire (and release)
page locks on all in-core pages that go beyond the new ->i_size, thus
waiting for completion of all page operations that began earlier. Only
after that it calls ->truncate(). See how it works? That's the reason why
on shrinking truncate() ->i_size *must* be set before the method call.
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