linux-kernel - [Resend PATCH 1/6] mm/memcg: warning on !memcg after readahead page charged

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Message-Id: <1597144232-11370-1-git-send-email-alex.shi@linux.alibaba.com>
Date:   Tue, 11 Aug 2020 19:10:27 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     akpm@...ux-foundation.org
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [Resend PATCH 1/6] mm/memcg: warning on !memcg after readahead page charged

Since readahead page is charged on memcg too, in theory we don't have to
check this exception now. Before safely remove them all, add a warning
for the unexpected !memcg.

Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: cgroups@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 include/linux/mmdebug.h | 13 +++++++++++++
 mm/memcontrol.c         | 15 ++++++++-------
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
index 2ad72d2c8cc5..4ed52879ce55 100644
--- a/include/linux/mmdebug.h
+++ b/include/linux/mmdebug.h
@@ -37,6 +37,18 @@
 			BUG();						\
 		}							\
 	} while (0)
+#define VM_WARN_ON_ONCE_PAGE(cond, page)	({			\
+	static bool __section(.data.once) __warned;			\
+	int __ret_warn_once = !!(cond);					\
+									\
+	if (unlikely(__ret_warn_once && !__warned)) {			\
+		dump_page(page, "VM_WARN_ON_ONCE_PAGE(" __stringify(cond)")");\
+		__warned = true;					\
+		WARN_ON(1);						\
+	}								\
+	unlikely(__ret_warn_once);					\
+})
+
 #define VM_WARN_ON(cond) (void)WARN_ON(cond)
 #define VM_WARN_ON_ONCE(cond) (void)WARN_ON_ONCE(cond)
 #define VM_WARN_ONCE(cond, format...) (void)WARN_ONCE(cond, format)
@@ -48,6 +60,7 @@
 #define VM_BUG_ON_MM(cond, mm) VM_BUG_ON(cond)
 #define VM_WARN_ON(cond) BUILD_BUG_ON_INVALID(cond)
 #define VM_WARN_ON_ONCE(cond) BUILD_BUG_ON_INVALID(cond)
+#define VM_WARN_ON_ONCE_PAGE(cond, page)  BUILD_BUG_ON_INVALID(cond)
 #define VM_WARN_ONCE(cond, format...) BUILD_BUG_ON_INVALID(cond)
 #define VM_WARN(cond, format...) BUILD_BUG_ON_INVALID(cond)
 #endif
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 130093bdf74b..299382fc55a9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1322,10 +1322,8 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
 	}
 
 	memcg = page->mem_cgroup;
-	/*
-	 * Swapcache readahead pages are added to the LRU - and
-	 * possibly migrated - before they are charged.
-	 */
+	/* Readahead page is charged too, to see if other page uncharged */
+	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
 		memcg = root_mem_cgroup;
 
@@ -6906,8 +6904,9 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
 	if (newpage->mem_cgroup)
 		return;
 
-	/* Swapcache readahead pages can get replaced before being charged */
 	memcg = oldpage->mem_cgroup;
+	/* Readahead page is charged too, to see if other page uncharged */
+	VM_WARN_ON_ONCE_PAGE(!memcg, oldpage);
 	if (!memcg)
 		return;
 
@@ -7104,7 +7103,8 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 
 	memcg = page->mem_cgroup;
 
-	/* Readahead page, never charged */
+	/* Readahead page is charged too, to see if other page uncharged */
+	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
 		return;
 
@@ -7168,7 +7168,8 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 
 	memcg = page->mem_cgroup;
 
-	/* Readahead page, never charged */
+	/* Readahead page is charged too, to see if other page uncharged */
+	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
 		return 0;
 
-- 
1.8.3.1