linux-kernel - [PATCH 11/11] PageSlab: eliminate unnecessary compound

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Date:   Tue, 12 Oct 2021 14:01:48 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     linux-mm@...ck.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH 11/11] PageSlab: eliminate unnecessary compound_head() calls in mm/memcontrol

page->memcg_data is generally not valid on tailpages, so the accessor
functions don't need to worry about encountering them outside of
bugs. The only place where the memory controller may encounter tail
pages is in mem_cgroup_from_obj(), but that uses virt_to_head_page()
first thing to resolve slab objects to slab pages.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 include/linux/memcontrol.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 02394f802698..3096c9a0ee01 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -397,7 +397,7 @@ static inline struct mem_cgroup *__page_memcg(struct page *page)
 {
 	unsigned long memcg_data = page->memcg_data;
 
-	VM_BUG_ON_PAGE(PageSlab(compound_head(page)), page);
+	VM_BUG_ON_PAGE(PageSlab(page), page);
 	VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_OBJCGS, page);
 	VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, page);
 
@@ -418,7 +418,7 @@ static inline struct obj_cgroup *__page_objcg(struct page *page)
 {
 	unsigned long memcg_data = page->memcg_data;
 
-	VM_BUG_ON_PAGE(PageSlab(compound_head(page)), page);
+	VM_BUG_ON_PAGE(PageSlab(page), page);
 	VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_OBJCGS, page);
 	VM_BUG_ON_PAGE(!(memcg_data & MEMCG_DATA_KMEM), page);
 
@@ -466,7 +466,7 @@ static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
 {
 	unsigned long memcg_data = READ_ONCE(page->memcg_data);
 
-	VM_BUG_ON_PAGE(PageSlab(compound_head(page)), page);
+	VM_BUG_ON_PAGE(PageSlab(page), page);
 	WARN_ON_ONCE(!rcu_read_lock_held());
 
 	if (memcg_data & MEMCG_DATA_KMEM) {
-- 
2.32.0