On 16.04.24 12:52, Lance Yang wrote:
On Tue, Apr 16, 2024 at 6:47 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
On 16.04.24 12:40, Lance Yang wrote:
Hey David,
Maybe I spotted a bug below.
Thanks for the review!
[...]
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;
+
+ /* A single mapping implies "mapped exclusively". */
+ if (mapcount <= 1)
+ return false;
+
+ /* If any page is mapped more than once we treat it "mapped shared". */
+ if (folio_entire_mapcount(folio) || mapcount > folio_nr_pages(folio))
+ return true;
bug: if a PMD-mapped THP is exclusively mapped, the folio_entire_mapcount()
function will return 1 (atomic_read(&folio->_entire_mapcount) + 1).
If it's exclusively mapped, then folio_mapcount(folio)==1. In which case
the previous statement:
if (mapcount <= 1)
return false;
Catches it.
You're right!
IOW, once we reach this point we now that folio_mapcount(folio) > 1, and
there must be something else besides the entire mapping ("more than once").
Or did I not address your concern?
Sorry, my mistake :(
No worries, thanks for the review and thinking this through!
--
Cheers,
David / dhildenb
