Re: [PATCH 00/28] Swap over NFS -v16

Peter Zijlstra
2008-02-26T15:44:11Z

On Tue, 2008-02-26 at 16:29 +0100, Miklos Szeredi wrote:
> > > mm-page_file_methods.patch
> > >
> > > This makes page_offset and others more expensive by adding a
> > > conditional jump to a function call that is not usually made.
> > >
> > > Why do swap pages have a different index to everyone else?
> >
> > Because the page->index of an anonymous page is related to its (anon)vma
> > so that it satisfies the constraints for vm_normal_page().
> >
> > The index in the swap file it totally unrelated and quite random. Hence
> > the swap-cache uses page->private to store it in.
>
> Yeah, and putting the condition into page_offset() will confuse code
> which uses it for finding the offset in the VMA or in a tmpfs file.
>
> So why not just have a separate page_swap_offset() function, used
> exclusively by swap_in/out()?

Ah, we can do the page_file_offset() to match page_file_index() and
page_file_mapping(). And convert NFS to use page_file_offset() where
appropriate, as I already did for these others.

That would sort out the mess, right?