Re: [PATCH v3 04/15] mm: update print_bad_page_map() to show anonymous page index

On Wed, Aug 05, 2026 at 10:01:52AM +0100, Lorenzo Stoakes (ARM) wrote:
> On Wed, Aug 05, 2026 at 04:30:18AM -0400, Gregory Price wrote:
> > On Mon, Aug 03, 2026 at 11:19:17AM +0100, Lorenzo Stoakes (ARM) wrote:
> > > On Mon, Aug 03, 2026 at 11:39:11AM +0200, David Hildenbrand (Arm) wrote:
> > > > On 7/30/26 08:32, Gregory Price wrote:
> > > > > On Wed, Jul 29, 2026 at 05:48:39PM +0100, Lorenzo Stoakes (ARM) wrote:
> > > > >> This is potentially useful debugging information and matches the existing
> > > > >> page offset provided.
> > > > >>
> > > > >> Use the raw __linear_anon_page_index() function so as to always output this
> > > > >> value regardless of whether the mapping is file-backed or not.
> > > > >>
> > > > >
> > > > > Begs the question whether we should mark the value based on whether
> > > > > it is file backed or not, but i suppose you can gleen that from the
> > > > > other printed values (anon_mem, mapping, vm_ops, etc).
> > > >
> > > > You mean something anon_pgoff_t or what did you have in mind?
> > >
> > > I suspect he means e.g. adding a (A) suffix or something? Like page offset xxx
> > > (F) or yyy (A) I guess?
> > >
> >
> > Yeah just an F/A in the print I suppose.  Sorry if that was unclear.
> >
> > If it saves someone the head-scratch of whether some bug is because it's
> > "file" or "true anon", given the ambiguity here, seems like maybe useful
> > debug information.
>
> Yeah will do on respin I think actually!
>
> I do think not providing that could result in some confusion like 'hm I
> thought this was file-backed'.
>
> (We've made our lives hard with varying definitions of 'anon'
> also... [shmem being 'anon in page cache' is especially lol] so it's
> already confusing but there we go :)
>
> I will add a comment explaining things so if anybody still wonders what's
> going on they can see what's up in the code.

Hmm actually at this point we'r printing a bad page mapping so don't have a
folio to know whether anon or file-backed.

So probably sensible:

	!vma_is_cow_mapping(vma) 			-> index: 0xf00
	vma_is_cow_mapping(vma) anon idx == file idx 	-> index: 0xf00
	otherwise 					-> index: 0xf00 (file) 0xba7 (anon)

Will do that in respin.

>
> >
> > ~Gregory
>
> --
> Cheers, Lorenzo

--
Cheers, Lorenzo