On 4/19/2024 5:19 PM, David Hildenbrand wrote:
On 19.04.24 04:29, Yin, Fengwei wrote:
On 4/10/2024 3:22 AM, David Hildenbrand wrote:
@@ -2200,7 +2200,22 @@ static inline size_t folio_size(struct folio
*folio)
*/
static inline bool folio_likely_mapped_shared(struct folio *folio)
{
- return page_mapcount(folio_page(folio, 0)) > 1;
+ int mapcount = folio_mapcount(folio);
+
+ /* Only partially-mappable folios require more care. */
+ if (!folio_test_large(folio) ||
unlikely(folio_test_hugetlb(folio)))
+ return mapcount > 1;
My understanding is that mapcount > folio_nr_pages(folio) can cover
order 0 folio. And also folio_entire_mapcount() can cover hugetlb (I am
not 100% sure for this one). I am wondering whether we can drop above
two lines? Thanks.
folio_entire_mapcount() does not apply to small folios, so we must not
call that for small folios.
Right. I missed this part. Thanks for clarification.
Regards
Yin, Fengwei
Regarding hugetlb, subpage mapcounts are completely unused, except
subpage 0 mapcount, which is now *always* negative (storing a page type)
-- so there is no trusting on that value at all.
So in the end, it all looked cleanest when only special-casing on
partially-mappable folios where we know the entire mapcount exists and
we know that subapge mapcount 0 actually stores something reasonable
(not a type).
Thanks!
