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

Alex Shi
2020-08-11T11:10:27Z

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>
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 | 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