On 12.06.25 18:49, Lorenzo Stoakes wrote:
On Wed, Jun 11, 2025 at 02:06:54PM +0200, David Hildenbrand wrote:
Marking PUDs that map a "normal" refcounted folios as special is
against our rules documented for vm_normal_page().
Might be worth referring to specifically which rule. I'm guessing it's the
general one of special == don't touch (from vm_normal_page() comment):
/*
* vm_normal_page -- This function gets the "struct page" associated with a
pte.
*
* "Special" mappings do not wish to be associated with a "struct page" (either
* it doesn't exist, or it exists but they don't want to touch it). In this
* case, NULL is returned here. "Normal" mappings do have a struct page.
*
* ...
*
*/
Well, yes, the one vm_normal_page() is all about ... ? :)
But don't we already violate this E.g.:
if (vma->vm_ops && vma->vm_ops->find_special_page)
return vma->vm_ops->find_special_page(vma, addr);
> > I mean this in itself perhaps means we should update this comment
to say 'except
when file-backed and there is a find_special_page() hook'.
I rather hope we severely break this case such that we can remove that hack.
Read as in: I couldn't care less about this XEN hack, in particular, not
documenting it.
I was already wondering about hiding it behind a XEN config so not each
and every sane user of this function has to perform this crappy-hack check.
[...]
}
- entry = pud_mkhuge(pfn_t_pud(pfn, prot));
- if (pfn_t_devmap(pfn))
- entry = pud_mkdevmap(entry);
- else
- entry = pud_mkspecial(entry);
+ if (fop.is_folio) {
+ entry = folio_mk_pud(fop.folio, vma->vm_page_prot);
+
+ folio_get(fop.folio);
+ folio_add_file_rmap_pud(fop.folio, &fop.folio->page, vma);
+ add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PUD_NR);
Nit, but might be nice to abstract for PMD/PUD.
Which part exactly? Likely a follow-up if it should be abstracted.
+ } else {
+ entry = pud_mkhuge(pfn_t_pud(fop.pfn, prot));
Same incredibly pedantic whitespace comment from previous patch :)
;)
--
Cheers,
David / dhildenb
