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

Ryan Roberts
2023-12-18T16:07:35Z

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@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> 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.

> + 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?

>
> VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
> - __folio_rmap_sanity_checks(folio, page, nr_pages, mode);
> -
> - /* Is page being mapped by PTE? Is this its first map to be added? */
> - 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;
> - }
>
> + nr = __folio_add_rmap(folio, page, nr_pages, mode, &nr_pmdmapped);
> if (nr_pmdmapped)
> __lruvec_stat_mod_folio(folio, folio_test_swapbacked(folio) ?
> NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);