Re: [PATCH rfc 3/4] mm: filemap: move __lruvec_stat_mod_folio() out of filemap_set_pte_range()

[Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>]

On 2024/5/7 19:11, David Hildenbrand wrote:
> On 29.04.24 09:24, Kefeng Wang wrote:
> > Adding __folio_add_file_rmap_ptes() which don't update lruvec stat, it
> > is used in filemap_set_pte_range(), with it, lruvec stat updating is
> > moved into the caller, no functional changes.
> >
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > ---
> >   include/linux/rmap.h |  2 ++
> >   mm/filemap.c         | 27 ++++++++++++++++++---------
> >   mm/rmap.c            | 16 ++++++++++++++++
> >   3 files changed, 36 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> > index 7229b9baf20d..43014ddd06f9 100644
> > --- a/include/linux/rmap.h
> > +++ b/include/linux/rmap.h
> > @@ -242,6 +242,8 @@ void folio_add_anon_rmap_pmd(struct folio *, 
> > struct page *,
> >           struct vm_area_struct *, unsigned long address, rmap_t flags);
> >   void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
> >           unsigned long address);
> > +int __folio_add_file_rmap_ptes(struct folio *, struct page *, int 
> > nr_pages,
> > +        struct vm_area_struct *);
> >   void folio_add_file_rmap_ptes(struct folio *, struct page *, int 
> > nr_pages,
> >           struct vm_area_struct *);
> >   #define folio_add_file_rmap_pte(folio, page, vma) \
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 7019692daddd..3966b6616d02 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -3501,14 +3501,15 @@ static struct folio 
> > *next_uptodate_folio(struct xa_state *xas,
> >   static void filemap_set_pte_range(struct vm_fault *vmf, struct folio 
> > *folio,
> >               struct page *page, unsigned int nr, unsigned long addr,
> > -            unsigned long *rss)
> > +            unsigned long *rss, int *nr_mapped)
> >   {
> >       struct vm_area_struct *vma = vmf->vma;
> >       pte_t entry;
> >       entry = prepare_range_pte_entry(vmf, false, folio, page, nr, addr);
> > -    folio_add_file_rmap_ptes(folio, page, nr, vma);
> > +    *nr_mapped += __folio_add_file_rmap_ptes(folio, page, nr, vma);
> > +
> >       set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr);
> >       /* no need to invalidate: a not-present page won't be cached */
> > @@ -3525,7 +3526,8 @@ static void filemap_set_pte_range(struct 
> > vm_fault *vmf, struct folio *folio,
> >   static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
> >               struct folio *folio, unsigned long start,
> >               unsigned long addr, unsigned int nr_pages,
> > -            unsigned long *rss, unsigned int *mmap_miss)
> > +            unsigned long *rss, int *nr_mapped,
> > +            unsigned int *mmap_miss)
> >   {
> >       vm_fault_t ret = 0;
> >       struct page *page = folio_page(folio, start);
> > @@ -3558,7 +3560,8 @@ static vm_fault_t filemap_map_folio_range(struct 
> > vm_fault *vmf,
> >           continue;
> >   skip:
> >           if (count) {
> > -            filemap_set_pte_range(vmf, folio, page, count, addr, rss);
> > +            filemap_set_pte_range(vmf, folio, page, count, addr,
> > +                          rss, nr_mapped);
> >               if (in_range(vmf->address, addr, count * PAGE_SIZE))
> >                   ret = VM_FAULT_NOPAGE;
> >           }
> > @@ -3571,7 +3574,8 @@ static vm_fault_t filemap_map_folio_range(struct 
> > vm_fault *vmf,
> >       } while (--nr_pages > 0);
> >       if (count) {
> > -        filemap_set_pte_range(vmf, folio, page, count, addr, rss);
> > +        filemap_set_pte_range(vmf, folio, page, count, addr, rss,
> > +                      nr_mapped);
> >           if (in_range(vmf->address, addr, count * PAGE_SIZE))
> >               ret = VM_FAULT_NOPAGE;
> >       }
> > @@ -3583,7 +3587,7 @@ static vm_fault_t filemap_map_folio_range(struct 
> > vm_fault *vmf,
> >   static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
> >           struct folio *folio, unsigned long addr,
> > -        unsigned long *rss, unsigned int *mmap_miss)
> > +        unsigned long *rss, int *nr_mapped, unsigned int *mmap_miss)
> >   {
> >       vm_fault_t ret = 0;
> >       struct page *page = &folio->page;
> > @@ -3606,7 +3610,7 @@ static vm_fault_t 
> > filemap_map_order0_folio(struct vm_fault *vmf,
> >       if (vmf->address == addr)
> >           ret = VM_FAULT_NOPAGE;
> > -    filemap_set_pte_range(vmf, folio, page, 1, addr, rss);
> > +    filemap_set_pte_range(vmf, folio, page, 1, addr, rss, nr_mapped);
> >       return ret;
> >   }
> > @@ -3646,6 +3650,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
> >       folio_type = mm_counter_file(folio);
> >       do {
> >           unsigned long end;
> > +        int nr_mapped = 0;
> >           addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
> >           vmf->pte += xas.xa_index - last_pgoff;
> > @@ -3655,11 +3660,15 @@ vm_fault_t filemap_map_pages(struct vm_fault 
> > *vmf,
> >           if (!folio_test_large(folio))
> >               ret |= filemap_map_order0_folio(vmf,
> > -                    folio, addr, &rss, &mmap_miss);
> > +                    folio, addr, &rss, &nr_mapped,
> > +                    &mmap_miss);
> >           else
> >               ret |= filemap_map_folio_range(vmf, folio,
> >                       xas.xa_index - folio->index, addr,
> > -                    nr_pages, &rss, &mmap_miss);
> > +                    nr_pages, &rss, &nr_mapped,
> > +                    &mmap_miss);
> > +
> > +        __lruvec_stat_mod_folio(folio, NR_FILE_MAPPED, nr_mapped);
> >           folio_unlock(folio);
> >           folio_put(folio);
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 2608c40dffad..55face4024f2 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1452,6 +1452,22 @@ static __always_inline void 
> > __folio_add_file_rmap(struct folio *folio,
> >           mlock_vma_folio(folio, vma);
> >   }
> > +int __folio_add_file_rmap_ptes(struct folio *folio, struct page *page,
> > +        int nr_pages, struct vm_area_struct *vma)
> > +{
> > +    int nr, nr_pmdmapped = 0;
> > +
> > +    VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
> > +
> > +    nr = __folio_add_rmap(folio, page, nr_pages, RMAP_LEVEL_PTE,
> > +                  &nr_pmdmapped);
> > +
> > +    /* See comments in folio_add_anon_rmap_*() */
> > +    if (!folio_test_large(folio))
> > +        mlock_vma_folio(folio, vma);
> > +
> > +    return nr;
> > +}
>
> I'm not really a fan :/ It does make the code more complicated, and it 
> will be harder to extend if we decide to ever account differently (e.g., 
> NR_SHMEM_MAPPED, additional tracking for mTHP etc).

If more different accounts, this may lead to bad scalability.
> With large folios we'll be naturally batching already here, and I do 

Yes, it is batched with large folios，but our fs is ext4/tmpfs, there
are not support large folio or still upstreaming.

> wonder, if this is really worth for performance, or if we could find 
> another way of batching (let the caller activate batching and drain 
> afterwards) without exposing these details to the caller.

It does reduce latency when batch lruvec stat updating without large
folio, but I can't find better way, or let's wait for the large folio
support on ext4/tmpfs, I also Cced memcg maintainers in patch4 to see if
there are any other ideas.


> Note that there is another cleanup happening [1].

The patch is related RMAP_LEVEL_PMD level, it should be not involved in 
filemap_map_pages().

> [1] 
> https://lore.kernel.org/all/20240506192924.271999-1-yosryahmed@xxxxxxxxxx/T/#u
>