Re: [PATCH v1 13/39] mm/rmap: factor out adding folio mappings into __folio_add_rmap()

[David Hildenbrand]

On 18.12.23 17:07, Ryan Roberts wrote:
> On 11/12/2023 15:56, David Hildenbrand wrote:
> > Let's factor it out to prepare for reuse as we convert
> > page_add_anon_rmap() to folio_add_anon_rmap_[pte|ptes|pmd]().
> >
> > Make the compiler always special-case on the granularity by using
> > __always_inline.
> >
> > Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > ---
> >   mm/rmap.c | 81 ++++++++++++++++++++++++++++++-------------------------
> >   1 file changed, 45 insertions(+), 36 deletions(-)
> >
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 2ff2f11275e5..c5761986a411 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1157,6 +1157,49 @@ int folio_total_mapcount(struct folio *folio)
> >   	return mapcount;
> >   }
> >   
> > +static __always_inline unsigned int __folio_add_rmap(struct folio *folio,
> > +		struct page *page, int nr_pages, enum rmap_mode mode,
> > +		unsigned int *nr_pmdmapped)
> > +{
> > +	atomic_t *mapped = &folio->_nr_pages_mapped;
> > +	int first, nr = 0;
> > +
> > +	__folio_rmap_sanity_checks(folio, page, nr_pages, mode);
> > +
> > +	/* Is page being mapped by PTE? Is this its first map to be added? */
>
> I suspect this comment is left over from the old version? It sounds a bit odd in
> its new context.

In this patch, I'm just moving the code, so it would have to be dropped 
in a previous patch.

I'm happy to drop all these comments in previous patches.

> > +	switch (mode) {
> > +	case RMAP_MODE_PTE:
> > +		do {
> > +			first = atomic_inc_and_test(&page->_mapcount);
> > +			if (first && folio_test_large(folio)) {
> > +				first = atomic_inc_return_relaxed(mapped);
> > +				first = (first < COMPOUND_MAPPED);
> > +			}
> > +
> > +			if (first)
> > +				nr++;
> > +		} while (page++, --nr_pages > 0);
> > +		break;
> > +	case RMAP_MODE_PMD:
> > +		first = atomic_inc_and_test(&folio->_entire_mapcount);
> > +		if (first) {
> > +			nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped);
> > +			if (likely(nr < COMPOUND_MAPPED + COMPOUND_MAPPED)) {
> > +				*nr_pmdmapped = folio_nr_pages(folio);
> > +				nr = *nr_pmdmapped - (nr & FOLIO_PAGES_MAPPED);
> > +				/* Raced ahead of a remove and another add? */
> > +				if (unlikely(nr < 0))
> > +					nr = 0;
> > +			} else {
> > +				/* Raced ahead of a remove of COMPOUND_MAPPED */
> > +				nr = 0;
> > +			}
> > +		}
> > +		break;
> > +	}
> > +	return nr;
> > +}
> > +
> >   /**
> >    * folio_move_anon_rmap - move a folio to our anon_vma
> >    * @folio:	The folio to move to our anon_vma
> > @@ -1380,45 +1423,11 @@ static __always_inline void __folio_add_file_rmap(struct folio *folio,
> >   		struct page *page, int nr_pages, struct vm_area_struct *vma,
> >   		enum rmap_mode mode)
> >   {
> > -	atomic_t *mapped = &folio->_nr_pages_mapped;
> > -	unsigned int nr_pmdmapped = 0, first;
> > -	int nr = 0;
> > +	unsigned int nr, nr_pmdmapped = 0;
>
> You're still being inconsistent with signed/unsigned here. Is there a reason
> these can't be signed like nr_pages in the interface?

I can turn them into signed values.

Personally, I think it's misleading to use "signed" for values that have 
absolutely no meaning for negative meaning. But sure, we can be 
consistent, at least in rmap code.

--
Cheers,

David / dhildenb