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mm/huge_memory.c: use head to check huge zero page

PATCH Applied Wei Yang 2 participants 4 messages Jan 10, 2020

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Memory management THP
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Wei Yang

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#0 lore raw

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

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 <[email protected]>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
mm/huge_memory.c +1 -1
index 168d8a1a9bac..90165f68cf13 100644
@@ -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);
Signature · 1 line
2.17.1
author
#1 lore raw

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

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 <[email protected]>
---
 mm/huge_memory.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)
mm/huge_memory.c +8 -8
index 90165f68cf13..69e623216211 100644
@@ -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);
Signature · 1 line
2.17.1
Acked-by on v1 2/2
#2 lore raw

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

Quoted 11 lines · 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 <[email protected]>
Acked-by Kirill A. Shutemov <[email protected]>
Signature · 1 line
 Kirill A. Shutemov