On 17/07/2023 17:48, David Hildenbrand wrote: > On 17.07.23 18:01, Ryan Roberts wrote: >> On 17/07/2023 16:42, David Hildenbrand wrote: >>> On 17.07.23 16:31, Ryan Roberts wrote: >>>> In preparation for the introduction of large folios for anonymous >>>> memory, we would like to be able to split them when they have unmapped >>>> subpages, in order to free those unused pages under memory pressure. So >>>> remove the artificial requirement that the large folio needed to be at >>>> least PMD-sized. >>>> >>>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >>>> Reviewed-by: Yu Zhao <yuzhao@xxxxxxxxxx> >>>> Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx> >>>> --- >>>> mm/rmap.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/mm/rmap.c b/mm/rmap.c >>>> index 0c0d8857dfce..2baf57d65c23 100644 >>>> --- a/mm/rmap.c >>>> +++ b/mm/rmap.c >>>> @@ -1430,7 +1430,7 @@ void page_remove_rmap(struct page *page, struct >>>> vm_area_struct *vma, >>>> * page of the folio is unmapped and at least one page >>>> * is still mapped. >>>> */ >>>> - if (folio_test_pmd_mappable(folio) && folio_test_anon(folio)) >>>> + if (folio_test_large(folio) && folio_test_anon(folio)) >>>> if (!compound || nr < nr_pmdmapped) >>>> deferred_split_folio(folio); >>> >>> !compound will always be true I guess, so nr_pmdmapped == 0 (which will always >>> be the case) will be ignored. >> >> I don't follow why !compound will always be true. This function is >> page_remove_rmap() (not folio_remove_rmap_range() which I add in a later patch). >> page_remove_rmap() can work on pmd-mapped pages where compound=true is passed in. > > I was talking about the folio_test_pmd_mappable() -> folio_test_large() change. > For folio_test_large() && !folio_test_pmd_mappable() I expect that we'll never > pass in "compound=true". > Sorry David, I've been staring at the code and your comment, and I still don't understand your point. I assumed you were trying to say that compound is always false and therefore "if (!compound || nr < nr_pmdmapped)" can be removed? But its not the case that compound is always false; it will be true when called to remove a pmd-mapped compound page. What change are you suggesting, exactly?
