[PATCH 1/2] mm/huge_memory.c: use head to check huge zero page

[PATCH 1/2] mm/huge_memory.c: use head to check huge zero page

[Wei Yang]

The page could be a tail page, if this is the case, this BUG_ON will
never be triggered.

Fixes: e9b61f19858a ("thp: reintroduce split_huge_page()")

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 168d8a1a9bac..90165f68cf13 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2696,7 +2696,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	unsigned long flags;
 	pgoff_t end;
 
-	VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
+	VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageCompound(page), page);
 
-- 
2.17.1

[PATCH 2/2] mm/huge_memory.c: use head to emphasize the purpose of page

[Wei Yang]

During split huge page, it checks the property of the page. Currently we
do the check on page and head without emphasizing the check is on the
compound page. In case the page passed to split_huge_page_to_list is a
tail page, audience would take some time to think about whether the
check is on compound page or tail page itself.

To make it explicit, use head instead of page for those checks. After
this, audience would be more clear about the checks are on compound page
and the page is used to do the split and dump error message if failed.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
---
 mm/huge_memory.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 90165f68cf13..69e623216211 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2688,7 +2688,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 {
 	struct page *head = compound_head(page);
 	struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
-	struct deferred_split *ds_queue = get_deferred_split_queue(page);
+	struct deferred_split *ds_queue = get_deferred_split_queue(head);
 	struct anon_vma *anon_vma = NULL;
 	struct address_space *mapping = NULL;
 	int count, mapcount, extra_pins, ret;
@@ -2697,10 +2697,10 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	pgoff_t end;
 
 	VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
-	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	VM_BUG_ON_PAGE(!PageCompound(page), page);
+	VM_BUG_ON_PAGE(!PageLocked(head), head);
+	VM_BUG_ON_PAGE(!PageCompound(head), head);
 
-	if (PageWriteback(page))
+	if (PageWriteback(head))
 		return -EBUSY;
 
 	if (PageAnon(head)) {
@@ -2751,7 +2751,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		goto out_unlock;
 	}
 
-	mlocked = PageMlocked(page);
+	mlocked = PageMlocked(head);
 	unmap_page(head);
 	VM_BUG_ON_PAGE(compound_mapcount(head), head);
 
@@ -2785,10 +2785,10 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		}
 		spin_unlock(&ds_queue->split_queue_lock);
 		if (mapping) {
-			if (PageSwapBacked(page))
-				__dec_node_page_state(page, NR_SHMEM_THPS);
+			if (PageSwapBacked(head))
+				__dec_node_page_state(head, NR_SHMEM_THPS);
 			else
-				__dec_node_page_state(page, NR_FILE_THPS);
+				__dec_node_page_state(head, NR_FILE_THPS);
 		}
 
 		__split_huge_page(page, list, end, flags);
-- 
2.17.1

Re: [PATCH 1/2] mm/huge_memory.c: use head to check huge zero page

[Kirill A. Shutemov]

On Fri, Jan 10, 2020 at 11:26:09AM +0800, Wei Yang wrote:
> The page could be a tail page, if this is the case, this BUG_ON will
> never be triggered.
> 
> Fixes: e9b61f19858a ("thp: reintroduce split_huge_page()")
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov

Re: [PATCH 2/2] mm/huge_memory.c: use head to emphasize the purpose of page

[Kirill A. Shutemov]

On Fri, Jan 10, 2020 at 11:26:10AM +0800, Wei Yang wrote:
> During split huge page, it checks the property of the page. Currently we
> do the check on page and head without emphasizing the check is on the
> compound page. In case the page passed to split_huge_page_to_list is a
> tail page, audience would take some time to think about whether the
> check is on compound page or tail page itself.
> 
> To make it explicit, use head instead of page for those checks. After
> this, audience would be more clear about the checks are on compound page
> and the page is used to do the split and dump error message if failed.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov