Re: [PATCH RFC 34/39] mm/rmap: introduce folio_try_dup_anon_rmap_[pte|ptes|pmd]()

[David Hildenbrand <david@xxxxxxxxxx>]

On 05.12.23 14:17, David Hildenbrand wrote:
> On 05.12.23 14:12, Ryan Roberts wrote:
> > On 04/12/2023 14:21, David Hildenbrand wrote:
> > > The last user of page_needs_cow_for_dma() and __page_dup_rmap() are gone,
> > > remove them.
> > >
> > > Add folio_try_dup_anon_rmap_ptes() right away, we want to perform rmap
> > > baching during fork() soon.
> > >
> > > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > > ---
> > >    include/linux/mm.h   |   6 --
> > >    include/linux/rmap.h | 145 +++++++++++++++++++++++++++++--------------
> > >    2 files changed, 100 insertions(+), 51 deletions(-)
> > >
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index 24c1c7c5a99c0..f7565b35ae931 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -1964,12 +1964,6 @@ static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
> > >    	return folio_maybe_dma_pinned(folio);
> > >    }
> > >    
> > > -static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
> > > -					  struct page *page)
> > > -{
> > > -	return folio_needs_cow_for_dma(vma, page_folio(page));
> > > -}
> > > -
> > >    /**
> > >     * is_zero_page - Query if a page is a zero page
> > >     * @page: The page to query
> > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> > > index 21d72cc602adc..84439f7720c62 100644
> > > --- a/include/linux/rmap.h
> > > +++ b/include/linux/rmap.h
> > > @@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio,
> > >    #endif
> > >    }
> > >    
> > > -static inline void __page_dup_rmap(struct page *page, bool compound)
> > > +static inline int __folio_try_dup_anon_rmap(struct folio *folio,
> >
> > __always_inline?
>
> Yes.
>
> > > +		struct page *page, unsigned int nr_pages,
> > > +		struct vm_area_struct *src_vma, enum rmap_mode mode)
> > >    {
> > > -	VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
> > > +	int i;
> > >    
> > > -	if (compound) {
> > > -		struct folio *folio = (struct folio *)page;
> > > +	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
> > >    
> > > -		VM_BUG_ON_PAGE(compound && !PageHead(page), page);
> > > -		atomic_inc(&folio->_entire_mapcount);
> > > -	} else {
> > > -		atomic_inc(&page->_mapcount);
> > > +	/*
> > > +	 * No need to check+clear for already shared PTEs/PMDs of the folio.
> > > +	 * This includes PTE mappings of (order-0) KSM folios.
> > > +	 */
> > > +	if (likely(mode == RMAP_MODE_PTE)) {
> >
> > Presumbly if __always_inline then the compiler will remove this if/else and just
> > keep the part indicated by mode? In which case "likely" is pretty useless? Same
> > for all similar sites in the other patches.
>
> Yes, also had this in mind. As long as we use __always_inline it
> shouldn't ever matter.

It seems to be cleanest to just do:

switch (mode) {
case RMAP_MODE_PTE:
	...
	break;
case RMAP_MODE_PMD:
	...
	break;
}

--
Cheers,

David / dhildenb