[Let's CC Johannes, Kamezewa and Kosaki]
On Mon 19-08-13 09:44:07, Michal Hocko wrote:
> On Sun 18-08-13 23:05:25, Hugh Dickins wrote:
[...]
> > Adding mem_cgroup_disabled() and once++ test there is ugly. Ideally,
> > even a !CONFIG_MEMCG build might in future have a stub root_mem_cgroup,
> > which would get around this: but that's not so at present.
> >
> > However, it appears that nothing actually dereferences the memcg pointer
> > in the mem_cgroup_disabled() case, here or anywhere else that case can
> > reach mem_cgroup_iter() (mem_cgroup_iter_break() is not called in
> > global reclaim).
> >
> > So, simply pass back an ordinarily-oopsing non-NULL address the first
> > time, and we shall hear about it if I'm wrong.
>
> This is a bit tricky but it seems like the easiest way for now. I will
> look at the fake root cgroup for !CONFIG_MEMCG.
OK, the following builds for both CONFIG_MEMCG enabled and disabled and
should work with cgroup_disable=memory as well as we are allocating
root_mem_cgroup for disabled case as well AFAICS.
It looks less scary than I expected. I haven't tested it yet but if you
think that it looks promising I will send a full patch with changelog.
---
>From 954085db1837874f94e0249e74b5ae1b49dcb9f8 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@xxxxxxx>
Date: Mon, 19 Aug 2013 10:51:07 +0200
Subject: [PATCH] memcg: add a fake root_mem_cgroup for !CONFIG_MEMCG
TODO proper changelog
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
include/linux/memcontrol.h | 8 ++++++--
mm/Makefile | 3 +++
mm/fake_root_memcg.c | 14 ++++++++++++++
mm/memcontrol.c | 17 +++++++++++++----
mm/vmscan.c | 8 ++++----
5 files changed, 40 insertions(+), 10 deletions(-)
create mode 100644 mm/fake_root_memcg.c
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 8a9ed4d..1d795a8 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -25,6 +25,8 @@
#include <linux/jump_label.h>
struct mem_cgroup;
+struct mem_cgroup *get_root_mem_cgroup(void);
+
struct page_cgroup;
struct page;
struct mm_struct;
@@ -370,7 +372,9 @@ mem_cgroup_iter_cond(struct mem_cgroup *root,
struct mem_cgroup_reclaim_cookie *reclaim,
mem_cgroup_iter_filter cond)
{
- return NULL;
+ if (prev)
+ return NULL;
+ return root;
}
static inline struct mem_cgroup *
@@ -378,7 +382,7 @@ mem_cgroup_iter(struct mem_cgroup *root,
struct mem_cgroup *prev,
struct mem_cgroup_reclaim_cookie *reclaim)
{
- return NULL;
+ return mem_cgroup_iter_cond(root, prev, reclaim, NULL);
}
static inline void mem_cgroup_iter_break(struct mem_cgroup *root,
diff --git a/mm/Makefile b/mm/Makefile
index 305d10a..fadc984 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -52,6 +52,9 @@ obj-$(CONFIG_MIGRATION) += migrate.o
obj-$(CONFIG_QUICKLIST) += quicklist.o
obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o
obj-$(CONFIG_MEMCG) += memcontrol.o page_cgroup.o vmpressure.o
+ifndef CONFIG_MEMCG
+ obj-y += fake_root_memcg.o
+endif
obj-$(CONFIG_CGROUP_HUGETLB) += hugetlb_cgroup.o
obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
diff --git a/mm/fake_root_memcg.c b/mm/fake_root_memcg.c
new file mode 100644
index 0000000..e98bd1e
--- /dev/null
+++ b/mm/fake_root_memcg.c
@@ -0,0 +1,14 @@
+#include <linux/memcontrol.h>
+
+/* Make a type placeholder for root_mem_cgroup. */
+struct mem_cgroup {};
+
+/*
+ * This is a fake root_mem_cgroup which will be used as a placeholder
+ * for !CONFIG_MEMCG.
+ */
+struct mem_cgroup root_mem_cgroup;
+struct mem_cgroup *get_root_mem_cgroup(void)
+{
+ return &root_mem_cgroup;
+}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b73988a..69ed11b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -68,6 +68,11 @@ EXPORT_SYMBOL(mem_cgroup_subsys);
#define MEM_CGROUP_RECLAIM_RETRIES 5
static struct mem_cgroup *root_mem_cgroup __read_mostly;
+struct mem_cgroup *get_root_mem_cgroup(void)
+{
+ return root_mem_cgroup;
+}
+
#ifdef CONFIG_MEMCG_SWAP
/* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
int do_swap_account __read_mostly;
@@ -1109,8 +1114,12 @@ struct mem_cgroup *mem_cgroup_iter_cond(struct mem_cgroup *root,
struct mem_cgroup *memcg = NULL;
struct mem_cgroup *last_visited = NULL;
- if (mem_cgroup_disabled())
- return NULL;
+ VM_BUG_ON(!root);
+ if (mem_cgroup_disabled()) {
+ if (prev)
+ return NULL;
+ return root;
+ }
if (!root)
root = root_mem_cgroup;
@@ -1198,9 +1207,9 @@ void mem_cgroup_iter_break(struct mem_cgroup *root,
iter = mem_cgroup_iter(root, iter, NULL))
#define for_each_mem_cgroup(iter) \
- for (iter = mem_cgroup_iter(NULL, NULL, NULL); \
+ for (iter = mem_cgroup_iter(root_mem_cgroup, NULL, NULL); \
iter != NULL; \
- iter = mem_cgroup_iter(NULL, iter, NULL))
+ iter = mem_cgroup_iter(root_mem_cgroup, iter, NULL))
void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx)
{
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a3bf7fd..d10b44a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2596,7 +2596,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
.may_swap = 1,
.order = order,
.priority = DEF_PRIORITY,
- .target_mem_cgroup = NULL,
+ .target_mem_cgroup = get_root_mem_cgroup(),
.nodemask = nodemask,
};
struct shrink_control shrink = {
@@ -2714,7 +2714,7 @@ static void age_active_anon(struct zone *zone, struct scan_control *sc)
if (!total_swap_pages)
return;
- memcg = mem_cgroup_iter(NULL, NULL, NULL);
+ memcg = mem_cgroup_iter(get_root_mem_cgroup(), NULL, NULL);
do {
struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
@@ -2722,7 +2722,7 @@ static void age_active_anon(struct zone *zone, struct scan_control *sc)
shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
sc, LRU_ACTIVE_ANON);
- memcg = mem_cgroup_iter(NULL, memcg, NULL);
+ memcg = mem_cgroup_iter(get_root_mem_cgroup(), memcg, NULL);
} while (memcg);
}
@@ -2949,7 +2949,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
.may_swap = 1,
.may_writepage = !laptop_mode,
.order = order,
- .target_mem_cgroup = NULL,
+ .target_mem_cgroup = get_root_mem_cgroup(),
};
count_vm_event(PAGEOUTRUN);
--
1.7.10.4
--
Michal Hocko
SUSE Labs
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