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

Miklos Szeredi
2008-02-26T15:30:30Z

> > 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()?

Miklos