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

David Hildenbrand
2023-12-18T17:06:09Z

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@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.

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