2020-11-02 02:20:14

by Alex Shi

Subject: [PATCH 0/2] bail out early for memcg disable

These 2 patches are indepenedent from per memcg lru lock, and may
encounter unexpected warning, so let's move out them from per memcg
lru locking patchset.

Alex Shi (2):
mm/memcg: bail early from swap accounting if memcg disabled
mm/memcg: warning on !memcg after readahead page charged

include/linux/mmdebug.h | 13 +++++++++++++
mm/memcontrol.c | 17 ++++++++++-------
2 files changed, 23 insertions(+), 7 deletions(-)

--
1.8.3.1

2020-11-02 02:20:17

by Alex Shi

Subject: [PATCH 2/2] mm/memcg: warning on !memcg after readahead page charged

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 <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
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 ec13fe4ed407..e46b9f9501c2 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;

@@ -7180,7 +7177,7 @@ 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;

@@ -7247,7 +7244,7 @@ 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

2020-11-02 02:21:58

by Alex Shi

Subject: [PATCH 1/2] mm/memcg: bail early from swap accounting if memcg disabled

We could bail out early when memcg wasn't enabled.

Signed-off-by: Alex Shi <[email protected]>
Reviewed-by: Roman Gushchin <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
mm/memcontrol.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3a24e3b619f5..ec13fe4ed407 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7172,6 +7172,9 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
VM_BUG_ON_PAGE(PageLRU(page), page);
VM_BUG_ON_PAGE(page_count(page), page);

+ if (mem_cgroup_disabled())
+ return;
+
if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
return;

@@ -7236,6 +7239,9 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
struct mem_cgroup *memcg;
unsigned short oldid;

+ if (mem_cgroup_disabled())
+ return 0;
+
if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
return 0;

--
1.8.3.1