Re: [PATCH v4 34/36] rmap: add folio_add_file_rmap_range()

[Yin Fengwei <nh26223@xxxxxxxxxx>]

On 2023/3/16 0:08, Ryan Roberts wrote:
> On 15/03/2023 13:34, Ryan Roberts wrote:
> > On 15/03/2023 05:14, Matthew Wilcox (Oracle) wrote:
> > > From: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> > >
> > > folio_add_file_rmap_range() allows to add pte mapping to a specific
> > > range of file folio. Comparing to page_add_file_rmap(), it batched
> > > updates __lruvec_stat for large folio.
> > >
> > > Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> > > ---
> > >   include/linux/rmap.h |  2 ++
> > >   mm/rmap.c            | 60 +++++++++++++++++++++++++++++++++-----------
> > >   2 files changed, 48 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> > > index b87d01660412..a3825ce81102 100644
> > > --- a/include/linux/rmap.h
> > > +++ b/include/linux/rmap.h
> > > @@ -198,6 +198,8 @@ void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
> > >   		unsigned long address);
> > >   void page_add_file_rmap(struct page *, struct vm_area_struct *,
> > >   		bool compound);
> > > +void folio_add_file_rmap_range(struct folio *, struct page *, unsigned int nr,
> > > +		struct vm_area_struct *, bool compound);
> > >   void page_remove_rmap(struct page *, struct vm_area_struct *,
> > >   		bool compound);
> > >   
> > > diff --git a/mm/rmap.c b/mm/rmap.c
> > > index 4898e10c569a..a91906b28835 100644
> > > --- a/mm/rmap.c
> > > +++ b/mm/rmap.c
> > > @@ -1301,31 +1301,39 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
> > >   }
> > >   
> > >   /**
> > > - * page_add_file_rmap - add pte mapping to a file page
> > > - * @page:	the page to add the mapping to
> > > + * folio_add_file_rmap_range - add pte mapping to page range of a folio
> > > + * @folio:	The folio to add the mapping to
> > > + * @page:	The first page to add
> > > + * @nr_pages:	The number of pages which will be mapped
> > >    * @vma:	the vm area in which the mapping is added
> > >    * @compound:	charge the page as compound or small page
> > >    *
> > > + * The page range of folio is defined by [first_page, first_page + nr_pages)
> > > + *
> > >    * The caller needs to hold the pte lock.
> > >    */
> > > -void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
> > > -		bool compound)
> > > +void folio_add_file_rmap_range(struct folio *folio, struct page *page,
> > > +			unsigned int nr_pages, struct vm_area_struct *vma,
> > > +			bool compound)
> > >   {
> > > -	struct folio *folio = page_folio(page);
> > >   	atomic_t *mapped = &folio->_nr_pages_mapped;
> > > -	int nr = 0, nr_pmdmapped = 0;
> > > -	bool first;
> > > +	unsigned int nr_pmdmapped = 0, first;
> > > +	int nr = 0;
> > >   
> > > -	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
> > > +	VM_WARN_ON_FOLIO(compound && !folio_test_pmd_mappable(folio), folio);
> > >   
> > >   	/* Is page being mapped by PTE? Is this its first map to be added? */
> > >   	if (likely(!compound)) {
> > > -		first = atomic_inc_and_test(&page->_mapcount);
> > > -		nr = first;
> > > -		if (first && folio_test_large(folio)) {
> > > -			nr = atomic_inc_return_relaxed(mapped);
> > > -			nr = (nr < COMPOUND_MAPPED);
> > > -		}
> > > +		do {
> > > +			first = atomic_inc_and_test(&page->_mapcount);
> > > +			if (first && folio_test_large(folio)) {
> > > +				first = atomic_inc_return_relaxed(mapped);
> > > +				first = (nr < COMPOUND_MAPPED);
> >
> > This still contains the typo that Yin Fengwei spotted in the previous version:
> > https://lore.kernel.org/linux-mm/20230228213738.272178-1-willy@xxxxxxxxxxxxx/T/#m84673899e25bc31356093a1177941f2cc35e5da8
> >
> > FYI, I'm seeing a perf regression of about 1% when compiling the kernel on
> > Ampere Altra (arm64) with this whole series on top of v6.3-rc1 (In a VM using
> > ext4 filesystem). Looks like instruction aborts are taking much longer and a
> > selection of syscalls are a bit slower. Still hunting down the root cause. Will
> > report once I have conclusive diagnosis.
>
> I'm sorry - I'm struggling to find the exact cause. But its spending over 2x the
> amount of time in the instruction abort handling code once patches 32-36 are
> included. Everything in the flame graph is just taking longer. Perhaps we are
> getting more instruction aborts somehow? I have the flamegraphs if anyone wants
> them - just shout and I'll email them separately.
Sorry for using another email. I am on travel and can't access my
company email now. Can you share the flamegraphs to me? I'd like
to take a look. As I remember, I didn't see the kernel build
regression w/o these patches on ext4/xfs. Thanks.


Regards
Yin, Fengwei

> > Thanks,
> > Ryan
> >
> >
> > > +			}
> > > +
> > > +			if (first)
> > > +				nr++;
> > > +		} while (page++, --nr_pages > 0);
> > >   	} else if (folio_test_pmd_mappable(folio)) {
> > >   		/* That test is redundant: it's for safety or to optimize out */
> > >   
> > > @@ -1354,6 +1362,30 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
> > >   	mlock_vma_folio(folio, vma, compound);
> > >   }
> > >   
> > > +/**
> > > + * page_add_file_rmap - add pte mapping to a file page
> > > + * @page:	the page to add the mapping to
> > > + * @vma:	the vm area in which the mapping is added
> > > + * @compound:	charge the page as compound or small page
> > > + *
> > > + * The caller needs to hold the pte lock.
> > > + */
> > > +void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
> > > +		bool compound)
> > > +{
> > > +	struct folio *folio = page_folio(page);
> > > +	unsigned int nr_pages;
> > > +

> > > +	VM_WARN_ON_ONCE_PAGE(compound && !PageTransHuge(page), page);
> > > +
> > > +	if (likely(!compound))
> > > +		nr_pages = 1;
> > > +	else
> > > +		nr_pages = folio_nr_pages(folio);
> > > +
> > > +	folio_add_file_rmap_range(folio, page, nr_pages, vma, compound);
> > > +}
> > > +
> > >   /**
> > >    * page_remove_rmap - take down pte mapping from a page
> > >    * @page:	page to remove mapping from