[PATCH v20 01/20] mm/memcg: warning on !memcg after readahead page charged

From: Alex Shi <alex.shi@linux.alibaba.com>
To: akpm@linux-foundation.org, mgorman@techsingularity.net,
	tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru,
	daniel.m.jordan@oracle.com, willy@infradead.org,
	hannes@cmpxchg.org, lkp@intel.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	shakeelb@google.com, iamjoonsoo.kim@lge.com,
	richard.weiyang@gmail.com, kirill@shutemov.name,
	alexander.duyck@gmail.com, rong.a.chen@intel.com,
	mhocko@suse.com, vdavydov.dev@gmail.com, shy828301@gmail.com
Cc: Michal Hocko <mhocko@kernel.org>
Subject: [PATCH v20 01/20] mm/memcg: warning on !memcg after readahead page charged
Date: Thu, 29 Oct 2020 18:44:46 +0800	[thread overview]
Message-ID: <1603968305-8026-2-git-send-email-alex.shi@linux.alibaba.com> (raw)
In-Reply-To: <1603968305-8026-1-git-send-email-alex.shi@linux.alibaba.com>

Add VM_WARN_ON_ONCE_PAGE() macro.

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@linux.alibaba.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: cgroups@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 include/linux/mmdebug.h | 13 +++++++++++++
 mm/memcontrol.c         | 11 ++++-------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
index 2ad72d2c8cc5..5d0767cb424a 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 3a24e3b619f5..6b67da305958 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1350,10 +1350,7 @@ 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.
-	 */
+	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
 		memcg = root_mem_cgroup;
 
@@ -6979,8 +6976,8 @@ 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;
+	VM_WARN_ON_ONCE_PAGE(!memcg, oldpage);
 	if (!memcg)
 		return;
 
@@ -7177,7 +7174,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 
 	memcg = page->mem_cgroup;
 
-	/* Readahead page, never charged */
+	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
 		return;
 
@@ -7241,7 +7238,7 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 
 	memcg = page->mem_cgroup;
 
-	/* Readahead page, never charged */
+	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
 		return 0;
 
-- 
1.8.3.1

