From: Roman Gushchin <guro@fb.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Shakeel Butt <shakeelb@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-mm@kvack.org>, <kernel-team@fb.com>,
Roman Gushchin <guro@fb.com>
Subject: [PATCH v3 3/4] mm: introduce page memcg flags
Date: Tue, 29 Sep 2020 16:59:19 -0700 [thread overview]
Message-ID: <20200929235920.537849-4-guro@fb.com> (raw)
In-Reply-To: <20200929235920.537849-1-guro@fb.com>
The lowest bit in page->memcg_data is used to distinguish between
struct memory_cgroup pointer and a pointer to a objcgs array.
All checks and modifications of this bit are open-coded.
Let's formalize it using page memcg flags, defined in enum
page_memcg_data_flags.
Additional flags might be added later.
Signed-off-by: Roman Gushchin <guro@fb.com>
---
include/linux/memcontrol.h | 35 ++++++++++++++++++++++++-----------
1 file changed, 24 insertions(+), 11 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d4d15c04bbaf..35f846c6b89b 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -343,6 +343,15 @@ struct mem_cgroup {
extern struct mem_cgroup *root_mem_cgroup;
+enum page_memcg_data_flags {
+ /* page->memcg_data is a pointer to an objcgs vector */
+ MEMCG_DATA_OBJCGS,
+ /* the next bit after the last actual flag */
+ __NR_MEMCG_DATA_FLAGS,
+};
+
+#define MEMCG_DATA_FLAGS_MASK ((0x1UL << __NR_MEMCG_DATA_FLAGS) - 1)
+
/*
* page_memcg - get the memory cgroup associated with a page
* @page: a pointer to the page struct
@@ -404,13 +413,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page)
*/
unsigned long memcg_data = READ_ONCE(page->memcg_data);
- /*
- * The lowest bit set means that memcg isn't a valid
- * memcg pointer, but a obj_cgroups pointer.
- * In this case the page is shared and doesn't belong
- * to any specific memory cgroup.
- */
- if (memcg_data & 0x1UL)
+ if (memcg_data & (0x1UL << MEMCG_DATA_OBJCGS))
return NULL;
return (struct mem_cgroup *)memcg_data;
@@ -459,7 +462,12 @@ static inline void clear_page_memcg(struct page *page)
*/
static inline struct obj_cgroup **page_objcgs(struct page *page)
{
- return (struct obj_cgroup **)(READ_ONCE(page->memcg_data) & ~0x1UL);
+ unsigned long memcg_data = READ_ONCE(page->memcg_data);
+
+ VM_BUG_ON_PAGE(memcg_data &&
+ !(memcg_data & (0x1UL << MEMCG_DATA_OBJCGS)), page);
+
+ return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
}
/*
@@ -474,8 +482,9 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
{
unsigned long memcg_data = READ_ONCE(page->memcg_data);
- if (memcg_data && (memcg_data & 0x1UL))
- return (struct obj_cgroup **)(memcg_data & ~0x1UL);
+ if (memcg_data && (memcg_data & (0x1UL << MEMCG_DATA_OBJCGS)))
+ return (struct obj_cgroup **)
+ (memcg_data & ~MEMCG_DATA_FLAGS_MASK);
return NULL;
}
@@ -490,7 +499,11 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page)
static inline bool set_page_objcgs(struct page *page,
struct obj_cgroup **objcgs)
{
- return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL);
+ unsigned long memcg_data = (unsigned long)objcgs;
+
+ memcg_data |= (0x1UL << MEMCG_DATA_OBJCGS);
+
+ return !cmpxchg(&page->memcg_data, 0, memcg_data);
}
/*
--
2.26.2
next prev parent reply other threads:[~2020-09-29 23:59 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-29 23:59 [PATCH v3 0/4] mm: allow mapping accounted kernel pages to userspace Roman Gushchin
2020-09-29 23:59 ` [PATCH v3 1/4] mm: memcontrol: use helpers to access page's memcg data Roman Gushchin
2020-09-30 20:32 ` Johannes Weiner
2020-09-29 23:59 ` [PATCH v3 2/4] mm: memcontrol/slab: use helpers to access slab page's memcg_data Roman Gushchin
2020-09-29 23:59 ` Roman Gushchin [this message]
2020-09-30 23:35 ` [PATCH v3 3/4] mm: introduce page memcg flags Shakeel Butt
2020-09-30 23:44 ` Roman Gushchin
2020-09-29 23:59 ` [PATCH v3 4/4] mm: convert page kmemcg type to a page memcg flag Roman Gushchin
2020-09-30 21:01 ` Johannes Weiner
2020-09-30 21:06 ` Johannes Weiner
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