Re: [patch 3/3] mm: fault handler to replace nopage and populate

Andrew Morton
2006-10-07T20:44:07Z

On Sat, 7 Oct 2006 15:06:32 +0200 (CEST)
Nick Piggin <npiggin@suse.de> wrote:

> Nonlinear mappings are (AFAIKS) simply a virtual memory concept that
> encodes the virtual address -> file offset differently from linear
> mappings.
>
> I can't see why the filesystem/pagecache code should need to know anything
> about it, except for the fact that the ->nopage handler didn't quite pass
> down enough information (ie. pgoff). But it is more logical to pass pgoff
> rather than have the ->nopage function calculate it itself anyway. And
> having the nopage handler install the pte itself is sort of nasty.
>
> This patch introduces a new fault handler that replaces ->nopage and ->populate
> and (hopefully) ->page_mkwrite. Most of the old mechanism is still in place
> so there is a lot of duplication and nice cleanups that can be removed if
> everyone switches over.
>
> The rationale for doing this in the first place is that nonlinear mappings
> are subject to the pagefault vs invalidate/truncate race too, and it seemed
> stupid to duplicate the synchronisation logic rather than just consolidate
> the two.

- You may find that gcc generates crap code for the initialisation of the
`struct fault_data'. If so, filling the fields in by hand one-at-a-time
will improve things.

- So is the plan here to migrate all code over to using
vm_operations.fault() and to finally remove vm_operations.nopage and
.nopfn? If so, that'd be nice.

- As you know, there is a case for constructing that `struct fault_data'
all the way up in do_no_page(): so we can pass data back, asking
do_no_page() to rerun the fault if we dropped mmap_sem.

- No useful opinion on the substance of this patch, sorry. It's Saturday ;)