On 17/07/2023 14:00, David Hildenbrand wrote:
> On 14.07.23 18:17, Ryan Roberts wrote:
>> In preparation for FLEXIBLE_THP support, improve
>> folio_add_new_anon_rmap() to allow a non-pmd-mappable, large folio to be
>> passed to it. In this case, all contained pages are accounted using the
>> order-0 folio (or base page) scheme.
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
>> Reviewed-by: Yu Zhao <yuzhao@xxxxxxxxxx>
>> Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
>> ---
>> mm/rmap.c | 28 +++++++++++++++++++++-------
>> 1 file changed, 21 insertions(+), 7 deletions(-)
>>
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 0c0d8857dfce..f293d072368a 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1278,31 +1278,45 @@ void page_add_anon_rmap(struct page *page, struct
>> vm_area_struct *vma,
>> * This means the inc-and-test can be bypassed.
>> * The folio does not have to be locked.
>> *
>> - * If the folio is large, it is accounted as a THP. As the folio
>> + * If the folio is pmd-mappable, it is accounted as a THP. As the folio
>> * is new, it's assumed to be mapped exclusively by a single process.
>> */
>> void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>> unsigned long address)
>> {
>> - int nr;
>> + int nr = folio_nr_pages(folio);
>>
>> - VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
>> + VM_BUG_ON_VMA(address < vma->vm_start ||
>> + address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
>> __folio_set_swapbacked(folio);
>>
>> - if (likely(!folio_test_pmd_mappable(folio))) {
>> + if (!folio_test_large(folio)) {
>
> Why remove the "likely" here? The patch itself does not change anything about
> that condition.
Good question; I'm not sure why. Will have to put it down to bad copy/paste
fixup. Will put it back in the next version.
>
>> /* increment count (starts at -1) */
>> atomic_set(&folio->_mapcount, 0);
>> - nr = 1;
>> + __page_set_anon_rmap(folio, &folio->page, vma, address, 1);
>> + } else if (!folio_test_pmd_mappable(folio)) {
>> + int i;
>> +
>> + for (i = 0; i < nr; i++) {
>> + struct page *page = folio_page(folio, i);
>> +
>> + /* increment count (starts at -1) */
>> + atomic_set(&page->_mapcount, 0);
>> + __page_set_anon_rmap(folio, page, vma,
>> + address + (i << PAGE_SHIFT), 1);
>> + }
>> +
>> + /* increment count (starts at 0) */
>
> That comment is a bit misleading. We're not talking about a mapcount as in the
> other cases here.
Correct, I'm talking about _nr_pages_mapped, which starts 0, not -1 like
_mapcount. The comment was intended to be in the style used in other similar
places in rmap.c. I could change it to: "_nr_pages_mapped is 0-based, so set it
to the number of pages in the folio" or remove it entirely? What do you prefer?
>
>> + atomic_set(&folio->_nr_pages_mapped, nr);
>> } else {
>> /* increment count (starts at -1) */
>> atomic_set(&folio->_entire_mapcount, 0);
>> atomic_set(&folio->_nr_pages_mapped, COMPOUND_MAPPED);
>> - nr = folio_nr_pages(folio);
>> + __page_set_anon_rmap(folio, &folio->page, vma, address, 1);
>> __lruvec_stat_mod_folio(folio, NR_ANON_THPS, nr);
>> }
>>
>
> Apart from that, LGTM.
>
