On 1/31/22 15:51, Mike Rapoport wrote:
On Mon, Jan 31, 2022 at 02:23:07PM -0500, Waiman Long wrote:
It was found that a number of offlined memcgs were not freed because
they were pinned by some charged pages that were present. Even "echo
1 > /proc/sys/vm/drop_caches" wasn't able to free those pages. These
offlined but not freed memcgs tend to increase in number over time with
the side effect that percpu memory consumption as shown in /proc/meminfo
also increases over time.
In order to find out more information about those pages that pin
offlined memcgs, the page_owner feature is extended to print memory
cgroup information especially whether the cgroup is offlined or not.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
---
mm/page_owner.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 28dac73e0542..a471c74c7fe0 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -10,6 +10,7 @@
#include <linux/migrate.h>
#include <linux/stackdepot.h>
#include <linux/seq_file.h>
+#include <linux/memcontrol.h>
#include <linux/sched/clock.h>
#include "internal.h"
@@ -325,6 +326,42 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
seq_putc(m, '\n');
}
+#ifdef CONFIG_MEMCG
+/*
+ * Looking for memcg information and print it out
+ */
+static inline void print_page_owner_memcg(char *kbuf, size_t count, int *pret,
+ struct page *page)
+{
+ unsigned long memcg_data = READ_ONCE(page->memcg_data);
+ struct mem_cgroup *memcg;
+ bool onlined;
+ char name[80];
+
+ if (!memcg_data)
+ return;
+
+ if (memcg_data & MEMCG_DATA_OBJCGS)
+ *pret += scnprintf(kbuf + *pret, count - *pret,
+ "Slab cache page\n");
Don't we need to check for overflow here?
See my previous patch 2 and the reason I used scnprintf() is that it
never return a length that is >= the given size. So overflow won't
happen. The final snprintf() in print_page_owner() will detect buffer
overflow.
+
+ memcg = page_memcg_check(page);
+ if (!memcg)
+ return;
+
+ onlined = (memcg->css.flags & CSS_ONLINE);
+ cgroup_name(memcg->css.cgroup, name, sizeof(name));
+ *pret += scnprintf(kbuf + *pret, count - *pret,
+ "Charged %sto %smemcg %s\n",
+ PageMemcgKmem(page) ? "(via objcg) " : "",
+ onlined ? "" : "offlined ",
+ name);
Ditto
+}
+#else /* CONFIG_MEMCG */
+static inline void print_page_owner_memcg(char *kbuf, size_t count, int *pret,
+ struct page *page) { }
I think #ifdef inside the print_page_owner_memcg() functions will be
simpler and clearer.
Yes, I see both styles used in kernel code though this style is probably
more common. I will keep this unless there is a good reason to do otherwise.
+#endif /* CONFIG_MEMCG */
+
static ssize_t
print_page_owner(char __user *buf, size_t count, unsigned long pfn,
struct page *page, struct page_owner *page_owner,
@@ -365,6 +402,8 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
migrate_reason_names[page_owner->last_migrate_reason]);
}
+ print_page_owner_memcg(kbuf, count, &ret, page);
+
ret can go over count here.
Why not make print_page_owner_memcg() an int so that the call will be
consistent with other calls in print_page_owner():
ret += print_page_owner_memcg(kbuf, count, page);
if (ret >= count)
goto err;
See my comments above.
Cheers,
Longman
