Kirill A. Shutemov wrote:
> Dave Hansen wrote:
> > Which reminds me... Why do we handle their reference counts differently? :)
> >
> > It seems like we could easily put a for loop in delete_from_page_cache()
> > that will release their reference counts along with the head page.
> > Wouldn't that make the code less special-cased for tail pages?
>
> delete_from_page_cache() is not the only user of
> __delete_from_page_cache()...
>
> It seems I did it wrong in add_to_page_cache_locked(). We shouldn't take
> references on tail pages there, only one on head. On split it will be
> distributed properly.
This way:
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b267859..c2c0df2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1556,6 +1556,7 @@ static void __split_huge_page_refcount(struct page *page,
struct zone *zone = page_zone(page);
struct lruvec *lruvec;
int tail_count = 0;
+ int init_tail_refcount;
/* prevent PageLRU to go away from under us, and freeze lru stats */
spin_lock_irq(&zone->lru_lock);
@@ -1565,6 +1566,13 @@ static void __split_huge_page_refcount(struct page *page,
/* complete memcg works before add pages to LRU */
mem_cgroup_split_huge_fixup(page);
+ /*
+ * When we add a huge page to page cache we take only reference to head
+ * page, but on split we need to take addition reference to all tail
+ * pages since they are still in page cache after splitting.
+ */
+ init_tail_refcount = PageAnon(page) ? 0 : 1;
+
for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
struct page *page_tail = page + i;
@@ -1587,8 +1595,9 @@ static void __split_huge_page_refcount(struct page *page,
* atomic_set() here would be safe on all archs (and
* not only on x86), it's safer to use atomic_add().
*/
- atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
- &page_tail->_count);
+ atomic_add(init_tail_refcount + page_mapcount(page) +
+ page_mapcount(page_tail) + 1,
+ &page_tail->_count);
/* after clearing PageTail the gup refcount can be released */
smp_mb();
--
Kirill A. Shutemov
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