On 12/7/22 4:38 PM, John Hubbard wrote:
On 12/7/22 14:37, Sidhartha Kumar wrote:
Document hugetlb's use of a zero compound order so support for zero
orders is not removed from folio_set_compound_order().
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Suggested-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
This can be folded into f2b67a51d0ef6871d4fb0c3e8199f278112bd108
mm: add folio dtor and order setter functions
include/linux/mm.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 443d496949a8..cd8508d728f1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -999,9 +999,16 @@ static inline void set_compound_order(struct page
*page, unsigned int order)
#endif
}
+/*
+ * folio_set_compound_order is generally passed a non-zero order to
+ * initialize a large folio. However, hugetlb code abuses this by
+ * passing in zero when 'dissolving' a large folio.
+ */
Wouldn't it be better to instead just create a new function for that
case, such as:
dissolve_large_folio()
Prior to the folio conversion, the helper function
__destroy_compound_gigantic_page() did:
set_compound_order(page, 0);
#ifdef CONFIG_64BIT
page[1].compound_nr = 0;
#endif
as part of dissolving the page. My goal for this patch was to create a
function that would encapsulate that segment of code with a single call
of folio_set_compound_order(folio, 0). set_compound_order() does not set
compound_nr to 0 when 0 is passed in to the order argument so explicitly
setting it is required. I don't think a separate dissolve_large_folio()
function for the hugetlb case is needed as
__destroy_compound_gigantic_folio() is pretty concise as it is.
?
static inline void folio_set_compound_order(struct folio *folio,
unsigned int order)
{
+ VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
+
folio->_folio_order = order;
#ifdef CONFIG_64BIT
folio->_folio_nr_pages = order ? 1U << order : 0;
thanks,
