[RFC][PATCH] memcg: add valid check at allocating or freeing memory

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

Hi,

I know we have many works to be done: THP, dirty limit, per-memcg background reclaim.
So, I'm not in hurry to push this patch.

This patch add checks at allocating or freeing a page whether the page is used
(iow, charged) from the view point of memcg. In fact, I've hit this check while
debugging a problem on RHEL6 kernel, which have stuck me these days and have not
been fixed unfortunately...

===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

This patch add checks at allocating or freeing a page whether the page is used
(iow, charged) from the view point of memcg.
This check may be usefull in debugging a problem and we did a similar checks
before the commit 52d4b9ac(memcg: allocate all page_cgroup at boot).

This patch adds some overheads at allocating or freeing memory, so it's enabled
only when CONFIG_DEBUG_VM is enabled.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
 include/linux/memcontrol.h |   12 +++++++++++
 mm/memcontrol.c            |   47 ++++++++++++++++++++++++++++++++++++++++++++
 mm/page_alloc.c            |    8 +++++-
 3 files changed, 65 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 067115c..04754c4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -146,6 +146,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 						gfp_t gfp_mask);
 u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
 
+bool mem_cgroup_bad_page_check(struct page *page);
+void mem_cgroup_print_bad_page(struct page *page);
 #else /* CONFIG_CGROUP_MEM_RES_CTLR */
 struct mem_cgroup;
 
@@ -336,6 +338,16 @@ u64 mem_cgroup_get_limit(struct mem_cgroup *mem)
 	return 0;
 }
 
+static inline bool
+mem_cgroup_bad_page_check(struct page *page)
+{
+	return false;
+}
+
+static void
+mem_cgroup_print_bad_page(struct page *page)
+{
+}
 #endif /* CONFIG_CGROUP_MEM_CONT */
 
 #endif /* _LINUX_MEMCONTROL_H */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7d89517..21af8b2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2971,6 +2971,53 @@ int mem_cgroup_shmem_charge_fallback(struct page *page,
 	return ret;
 }
 
+#ifdef CONFIG_DEBUG_VM
+static bool
+__mem_cgroup_bad_page_check(struct page *page, struct page_cgroup **pcp)
+{
+	struct page_cgroup *pc;
+	bool ret = false;
+
+	pc = lookup_page_cgroup(page);
+	if (unlikely(!pc))
+		goto out;
+
+	if (PageCgroupUsed(pc)) {
+		ret = true;
+		if (pcp)
+			*pcp = pc;
+	}
+out:
+	return ret;
+}
+
+bool mem_cgroup_bad_page_check(struct page *page)
+{
+	if (mem_cgroup_disabled())
+		return false;
+
+	return __mem_cgroup_bad_page_check(page, NULL);
+}
+
+void mem_cgroup_print_bad_page(struct page *page)
+{
+	struct page_cgroup *pc;
+
+	if (__mem_cgroup_bad_page_check(page, &pc))
+		printk(KERN_ALERT "pc:%p pc->flags:%ld pc->mem_cgroup:%p\n",
+			pc, pc->flags, pc->mem_cgroup);
+}
+#else
+bool mem_cgroup_bad_page_check(struct page *page)
+{
+	return false;
+}
+
+void mem_cgroup_print_bad_page(struct page *page)
+{
+}
+#endif
+
 static DEFINE_MUTEX(set_limit_mutex);
 
 static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7650ceb..5caeda8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -53,6 +53,7 @@
 #include <linux/compaction.h>
 #include <trace/events/kmem.h>
 #include <linux/ftrace_event.h>
+#include <linux/memcontrol.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -570,7 +571,8 @@ static inline int free_pages_check(struct page *page)
 	if (unlikely(page_mapcount(page) |
 		(page->mapping != NULL)  |
 		(atomic_read(&page->_count) != 0) |
-		(page->flags & PAGE_FLAGS_CHECK_AT_FREE))) {
+		(page->flags & PAGE_FLAGS_CHECK_AT_FREE) |
+		(mem_cgroup_bad_page_check(page)))) {
 		bad_page(page);
 		return 1;
 	}
@@ -755,7 +757,8 @@ static inline int check_new_page(struct page *page)
 	if (unlikely(page_mapcount(page) |
 		(page->mapping != NULL)  |
 		(atomic_read(&page->_count) != 0)  |
-		(page->flags & PAGE_FLAGS_CHECK_AT_PREP))) {
+		(page->flags & PAGE_FLAGS_CHECK_AT_PREP) |
+		(mem_cgroup_bad_page_check(page)))) {
 		bad_page(page);
 		return 1;
 	}
@@ -5627,4 +5630,5 @@ void dump_page(struct page *page)
 		page, atomic_read(&page->_count), page_mapcount(page),
 		page->mapping, page->index);
 	dump_page_flags(page->flags);
+	mem_cgroup_print_bad_page(page);
 }
-- 
1.7.1

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