Re: [PATCH RFC 23/39] mm/rmap: introduce folio_remove_rmap_[pte|ptes|pmd]()

[David Hildenbrand]

> > +static __always_inline void __folio_remove_rmap(struct folio *folio,
> > +		struct page *page, unsigned int nr_pages,
> > +		struct vm_area_struct *vma, enum rmap_mode mode)
> > +{
> >   	atomic_t *mapped = &folio->_nr_pages_mapped;
> > -	int nr = 0, nr_pmdmapped = 0;
> > -	bool last;
> > +	int last, nr = 0, nr_pmdmapped = 0;
>
> nit: you're being inconsistent across the functions with signed vs unsigned for
> page counts (e.g. nr, nr_pmdmapped) - see __folio_add_rmap(),
> __folio_add_file_rmap(), __folio_add_anon_rmap().

Definitely.

> I suggest pick one and stick to it. Personally I'd go with signed int (since
> that's what all the counters in struct folio that we are manipulating are,
> underneath the atomic_t) then check that nr_pages > 0 in
> __folio_rmap_sanity_checks().

Can do, but note that the counters are signed to detect udnerflows. It 
doesn't make sense here to pass a negative number.

> >   	enum node_stat_item idx;
> >   
> > -	VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
> > -	VM_BUG_ON_PAGE(compound && !PageHead(page), page);
> > +	__folio_rmap_sanity_checks(folio, page, nr_pages, mode);
> >   
> >   	/* Is page being unmapped by PTE? Is this its last map to be removed? */
> > -	if (likely(!compound)) {
> > -		last = atomic_add_negative(-1, &page->_mapcount);
> > -		nr = last;
> > -		if (last && folio_test_large(folio)) {
> > -			nr = atomic_dec_return_relaxed(mapped);
> > -			nr = (nr < COMPOUND_MAPPED);
> > -		}
> > -	} else if (folio_test_pmd_mappable(folio)) {
> > -		/* That test is redundant: it's for safety or to optimize out */
> > +	if (likely(mode == RMAP_MODE_PTE)) {
> > +		do {
> > +			last = atomic_add_negative(-1, &page->_mapcount);
> > +			if (last && folio_test_large(folio)) {
> > +				last = atomic_dec_return_relaxed(mapped);
> > +				last = (last < COMPOUND_MAPPED);
> > +			}
> >   
> > +			if (last)
> > +				nr++;
> > +		} while (page++, --nr_pages > 0);
> > +	} else if (mode == RMAP_MODE_PMD) {
> >   		last = atomic_add_negative(-1, &folio->_entire_mapcount);
> >   		if (last) {
> >   			nr = atomic_sub_return_relaxed(COMPOUND_MAPPED, mapped);
> > @@ -1517,7 +1528,7 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
> >   		 * is still mapped.
> >   		 */
> >   		if (folio_test_pmd_mappable(folio) && folio_test_anon(folio))
>
> folio_test_pmd_mappable() -> folio_test_large()
>
> Since you're converting this to support batch PTE removal, it might as well also
> support smaller-than-pmd too?

I remember that you have a patch for that, right? :)

> I currently have a patch to do this same change in the multi-size THP series.

Ah, yes, and that should go in first.


--
Cheers,

David / dhildenb