[PATCH v3 1/4] mm: memcontrol: use helpers to access page's memcg data

From: Roman Gushchin
Date: Tue Sep 29 2020 - 19:59:41 EST

Currently there are many open-coded reads and writes of the
page->mem_cgroup pointer, as well as a couple of read helpers,
which are barely used.

It creates an obstacle on a way to reuse some bits of the pointer
for storing additional bits of information. In fact, we already do
this for slab pages, where the last bit indicates that a pointer has
an attached vector of objcg pointers instead of a regular memcg
pointer.

This commits uses 2 existing helpers and introduces 3 new helpers to
converts all raw accesses to page->mem_cgroup to calls of these helpers:
struct mem_cgroup *page_memcg(struct page *page);
struct mem_cgroup *page_memcg_rcu(struct page *page);
struct mem_cgroup *page_memcg_check(struct page *page);
void set_page_memcg(struct page *page, struct mem_cgroup *memcg);
void clear_page_memcg(struct page *page);

page_memcg_check() is intended to be used in cases when the page
can be a slab page and have a memcg pointer pointing at objcg vector.
It does check the lowest bit, and if set, returns NULL.
page_memcg() contains a VM_BUG_ON_PAGE() check for the page not
being a slab page. So do set_page_memcg() and clear_page_memcg().

To make sure nobody uses a direct access, struct page's
mem_cgroup/obj_cgroups is converted to unsigned long memcg_data.
Only new helpers and a couple of slab-accounting related functions
access this field directly.

Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
fs/buffer.c | 2 +-
fs/iomap/buffered-io.c | 2 +-
include/linux/memcontrol.h | 153 +++++++++++++++++++++++++++++--
include/linux/mm.h | 22 -----
include/linux/mm_types.h | 5 +-
include/trace/events/writeback.h | 2 +-
kernel/fork.c | 7 +-
mm/debug.c | 4 +-
mm/huge_memory.c | 4 +-
mm/memcontrol.c | 121 +++++++++++-------------
mm/page_alloc.c | 4 +-
mm/page_io.c | 6 +-
mm/slab.h | 9 +-
mm/workingset.c | 2 +-
14 files changed, 223 insertions(+), 120 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index bf4d8037f91b..64564ac7dcc5 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -657,7 +657,7 @@ int __set_page_dirty_buffers(struct page *page)
} while (bh != head);
}
/*
- * Lock out page->mem_cgroup migration to keep PageDirty
+ * Lock out page's memcg migration to keep PageDirty
* synchronized with per-memcg dirty page counters.
*/
lock_page_memcg(page);
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 897ab9a26a74..71381931f2c3 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -669,7 +669,7 @@ iomap_set_page_dirty(struct page *page)
return !TestSetPageDirty(page);

/*
- * Lock out page->mem_cgroup migration to keep PageDirty
+ * Lock out page's memcg migration to keep PageDirty
* synchronized with per-memcg dirty page counters.
*/
lock_page_memcg(page);
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e391e3c56de5..31ab1639e0fe 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -343,6 +343,109 @@ struct mem_cgroup {

extern struct mem_cgroup *root_mem_cgroup;

+/*
+ * page_memcg - get the memory cgroup associated with a page
+ * @page: a pointer to the page struct
+ *
+ * Returns a pointer to the memory cgroup associated with the page,
+ * or NULL. This function assumes that the page is known to have a
+ * proper memory cgroup pointer. It's not safe to call this function
+ * against some type of pages, e.g. slab pages or ex-slab pages.
+ *
+ * Any of the following ensures page and memcg binding stability:
+ * - the page lock
+ * - LRU isolation
+ * - lock_page_memcg()
+ * - exclusive reference
+ */
+static inline struct mem_cgroup *page_memcg(struct page *page)
+{
+ VM_BUG_ON_PAGE(PageSlab(page), page);
+ return (struct mem_cgroup *)page->memcg_data;
+}
+
+/*
+ * page_memcg_rcu - locklessly get the memory cgroup associated with a page
+ * @page: a pointer to the page struct
+ *
+ * Returns a pointer to the memory cgroup associated with the page,
+ * or NULL. This function assumes that the page is known to have a
+ * proper memory cgroup pointer. It's not safe to call this function
+ * against some type of pages, e.g. slab pages or ex-slab pages.
+ */
+static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
+{
+ VM_BUG_ON_PAGE(PageSlab(page), page);
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
+ return (struct mem_cgroup *)READ_ONCE(page->memcg_data);
+}
+
+/*
+ * page_memcg_check - get the memory cgroup associated with a page
+ * @page: a pointer to the page struct
+ *
+ * Returns a pointer to the memory cgroup associated with the page,
+ * or NULL. This function unlike page_memcg() can take any page
+ * as an argument. It has to be used in cases when it's not known if a page
+ * has an associated memory cgroup pointer or an object cgroups vector.
+ *
+ * Any of the following ensures page and memcg binding stability:
+ * - the page lock
+ * - LRU isolation
+ * - lock_page_memcg()
+ * - exclusive reference
+ */
+static inline struct mem_cgroup *page_memcg_check(struct page *page)
+{
+ /*
+ * Because page->memcg_data might be changed asynchronously
+ * for slab pages, READ_ONCE() should be used here.
+ */
+ 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)
+ return NULL;
+
+ return (struct mem_cgroup *)memcg_data;
+}
+
+/*
+ * set_page_memcg - associate a page with a memory cgroup
+ * @page: a pointer to the page struct
+ * @memcg: a pointer to the memory cgroup
+ *
+ * Associates a page with a memory cgroup.
+ */
+static inline void set_page_memcg(struct page *page, struct mem_cgroup *memcg)
+{
+ VM_BUG_ON_PAGE(PageSlab(page), page);
+
+ /*
+ * Please, refer to page_memcg()'s description for the page and memcg
+ * binding stability requirements.
+ */
+ page->memcg_data = (unsigned long)memcg;
+}
+
+/*
+ * clear_page_memcg - clear an association of a page with a memory cgroup
+ * @page: a pointer to the page struct
+ *
+ * Clears an association of a page with a memory cgroup.
+ */
+static inline void clear_page_memcg(struct page *page)
+{
+ VM_BUG_ON_PAGE(PageSlab(page), page);
+ page->memcg_data = 0;
+}
+
static __always_inline bool memcg_stat_item_in_bytes(int idx)
{
if (idx == MEMCG_PERCPU_B)
@@ -743,15 +846,19 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg,
static inline void __mod_memcg_page_state(struct page *page,
int idx, int val)
{
- if (page->mem_cgroup)
- __mod_memcg_state(page->mem_cgroup, idx, val);
+ struct mem_cgroup *memcg = page_memcg(page);
+
+ if (memcg)
+ __mod_memcg_state(memcg, idx, val);
}

static inline void mod_memcg_page_state(struct page *page,
int idx, int val)
{
- if (page->mem_cgroup)
- mod_memcg_state(page->mem_cgroup, idx, val);
+ struct mem_cgroup *memcg = page_memcg(page);
+
+ if (memcg)
+ mod_memcg_state(memcg, idx, val);
}

static inline unsigned long lruvec_page_state(struct lruvec *lruvec,
@@ -834,16 +941,17 @@ static inline void __mod_lruvec_page_state(struct page *page,
enum node_stat_item idx, int val)
{
struct page *head = compound_head(page); /* rmap on tail pages */
+ struct mem_cgroup *memcg = page_memcg(head);
pg_data_t *pgdat = page_pgdat(page);
struct lruvec *lruvec;

/* Untracked pages have no memcg, no lruvec. Update only the node */
- if (!head->mem_cgroup) {
+ if (!memcg) {
__mod_node_page_state(pgdat, idx, val);
return;
}

- lruvec = mem_cgroup_lruvec(head->mem_cgroup, pgdat);
+ lruvec = mem_cgroup_lruvec(memcg, pgdat);
__mod_lruvec_state(lruvec, idx, val);
}

@@ -878,8 +986,10 @@ static inline void count_memcg_events(struct mem_cgroup *memcg,
static inline void count_memcg_page_event(struct page *page,
enum vm_event_item idx)
{
- if (page->mem_cgroup)
- count_memcg_events(page->mem_cgroup, idx, 1);
+ struct mem_cgroup *memcg = page_memcg(page);
+
+ if (memcg)
+ count_memcg_events(memcg, idx, 1);
}

static inline void count_memcg_event_mm(struct mm_struct *mm,
@@ -941,6 +1051,31 @@ void mem_cgroup_split_huge_fixup(struct page *head);

struct mem_cgroup;

+static inline struct mem_cgroup *page_memcg(struct page *page)
+{
+ return NULL;
+}
+
+static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
+{
+ WARN_ON_ONCE(!rcu_read_lock_held());
+ return NULL;
+}
+
+static inline struct mem_cgroup *page_memcg_check(struct page *page)
+{
+ return NULL;
+}
+
+static inline void set_page_memcg(struct page *page,
+ struct mem_cgroup *memcg)
+{
+}
+
+static inline void clear_page_memcg(struct page *page)
+{
+}
+
static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
{
return true;
@@ -1430,7 +1565,7 @@ static inline void mem_cgroup_track_foreign_dirty(struct page *page,
if (mem_cgroup_disabled())
return;

- if (unlikely(&page->mem_cgroup->css != wb->memcg_css))
+ if (unlikely(&page_memcg(page)->css != wb->memcg_css))
mem_cgroup_track_foreign_dirty_slowpath(page, wb);
}

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 17e712207d74..5e24ff2ffec9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1476,28 +1476,6 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
#endif
}

-#ifdef CONFIG_MEMCG
-static inline struct mem_cgroup *page_memcg(struct page *page)
-{
- return page->mem_cgroup;
-}
-static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
-{
- WARN_ON_ONCE(!rcu_read_lock_held());
- return READ_ONCE(page->mem_cgroup);
-}
-#else
-static inline struct mem_cgroup *page_memcg(struct page *page)
-{
- return NULL;
-}
-static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
-{
- WARN_ON_ONCE(!rcu_read_lock_held());
- return NULL;
-}
-#endif
-
/*
* Some inline functions in vmstat.h depend on page_zone()
*/
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 496c3ff97cce..4856d23b1161 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -199,10 +199,7 @@ struct page {
atomic_t _refcount;

#ifdef CONFIG_MEMCG
- union {
- struct mem_cgroup *mem_cgroup;
- struct obj_cgroup **obj_cgroups;
- };
+ unsigned long memcg_data;
#endif

/*
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index e7cbccc7c14c..39a40dfb578a 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -257,7 +257,7 @@ TRACE_EVENT(track_foreign_dirty,
__entry->ino = inode ? inode->i_ino : 0;
__entry->memcg_id = wb->memcg_css->id;
__entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
- __entry->page_cgroup_ino = cgroup_ino(page->mem_cgroup->css.cgroup);
+ __entry->page_cgroup_ino = cgroup_ino(page_memcg(page)->css.cgroup);
),

TP_printk("bdi %s[%llu]: ino=%lu memcg_id=%u cgroup_ino=%lu page_cgroup_ino=%lu",
diff --git a/kernel/fork.c b/kernel/fork.c
index 138cd6ca50da..ecbd44831130 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -403,9 +403,10 @@ static int memcg_charge_kernel_stack(struct task_struct *tsk)

for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
/*
- * If memcg_kmem_charge_page() fails, page->mem_cgroup
- * pointer is NULL, and memcg_kmem_uncharge_page() in
- * free_thread_stack() will ignore this page.
+ * If memcg_kmem_charge_page() fails, page's
+ * memory cgroup pointer is NULL, and
+ * memcg_kmem_uncharge_page() in free_thread_stack()
+ * will ignore this page.
*/
ret = memcg_kmem_charge_page(vm->pages[i], GFP_KERNEL,
0);
diff --git a/mm/debug.c b/mm/debug.c
index ccca576b2899..8a40b3fefbeb 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -182,8 +182,8 @@ void __dump_page(struct page *page, const char *reason)
pr_warn("page dumped because: %s\n", reason);

#ifdef CONFIG_MEMCG
- if (!page_poisoned && page->mem_cgroup)
- pr_warn("page->mem_cgroup:%px\n", page->mem_cgroup);
+ if (!page_poisoned && page->memcg_data)
+ pr_warn("pages's memcg:%lx\n", page->memcg_data);
#endif
}

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b1c7dc8a6f96..6df8a80b5bc9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -470,7 +470,7 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
#ifdef CONFIG_MEMCG
static inline struct deferred_split *get_deferred_split_queue(struct page *page)
{
- struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
+ struct mem_cgroup *memcg = page_memcg(compound_head(page));
struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));

if (memcg)
@@ -2735,7 +2735,7 @@ void deferred_split_huge_page(struct page *page)
{
struct deferred_split *ds_queue = get_deferred_split_queue(page);
#ifdef CONFIG_MEMCG
- struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
+ struct mem_cgroup *memcg = page_memcg(compound_head(page));
#endif
unsigned long flags;

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9c4a0851348f..dfb10eccb0e5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -533,7 +533,7 @@ struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page)
{
struct mem_cgroup *memcg;

- memcg = page->mem_cgroup;
+ memcg = page_memcg(page);

if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
memcg = root_mem_cgroup;
@@ -560,16 +560,7 @@ ino_t page_cgroup_ino(struct page *page)
unsigned long ino = 0;

rcu_read_lock();
- memcg = page->mem_cgroup;
-
- /*
- * 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 ((unsigned long) memcg & 0x1UL)
- memcg = NULL;
+ memcg = page_memcg_check(page);

while (memcg && !(memcg->css.flags & CSS_ONLINE))
memcg = parent_mem_cgroup(memcg);
@@ -1050,7 +1041,7 @@ EXPORT_SYMBOL(get_mem_cgroup_from_mm);
*/
struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)
{
- struct mem_cgroup *memcg = page->mem_cgroup;
+ struct mem_cgroup *memcg = page_memcg(page);

if (mem_cgroup_disabled())
return NULL;
@@ -1349,7 +1340,7 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
goto out;
}

- memcg = page->mem_cgroup;
+ memcg = page_memcg(page);
/*
* Swapcache readahead pages are added to the LRU - and
* possibly migrated - before they are charged.
@@ -2105,7 +2096,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
}

/**
- * lock_page_memcg - lock a page->mem_cgroup binding
+ * lock_page_memcg - lock a page and memcg binding
* @page: the page
*
* This function protects unlocked LRU pages from being moved to
@@ -2137,7 +2128,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page)
if (mem_cgroup_disabled())
return NULL;
again:
- memcg = head->mem_cgroup;
+ memcg = page_memcg(head);
if (unlikely(!memcg))
return NULL;

@@ -2145,7 +2136,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page)
return memcg;

spin_lock_irqsave(&memcg->move_lock, flags);
- if (memcg != head->mem_cgroup) {
+ if (memcg != page_memcg(head)) {
spin_unlock_irqrestore(&memcg->move_lock, flags);
goto again;
}
@@ -2183,14 +2174,14 @@ void __unlock_page_memcg(struct mem_cgroup *memcg)
}

/**
- * unlock_page_memcg - unlock a page->mem_cgroup binding
+ * unlock_page_memcg - unlock a page and memcg binding
* @page: the page
*/
void unlock_page_memcg(struct page *page)
{
struct page *head = compound_head(page);

- __unlock_page_memcg(head->mem_cgroup);
+ __unlock_page_memcg(page_memcg(head));
}
EXPORT_SYMBOL(unlock_page_memcg);

@@ -2880,7 +2871,7 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)

static void commit_charge(struct page *page, struct mem_cgroup *memcg)
{
- VM_BUG_ON_PAGE(page->mem_cgroup, page);
+ VM_BUG_ON_PAGE(page_memcg(page), page);
/*
* Any of the following ensures page->mem_cgroup stability:
*
@@ -2889,7 +2880,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg)
* - lock_page_memcg()
* - exclusive reference
*/
- page->mem_cgroup = memcg;
+ set_page_memcg(page, memcg);
}

#ifdef CONFIG_MEMCG_KMEM
@@ -2904,8 +2895,7 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
if (!vec)
return -ENOMEM;

- if (cmpxchg(&page->obj_cgroups, NULL,
- (struct obj_cgroup **) ((unsigned long)vec | 0x1UL)))
+ if (cmpxchg(&page->memcg_data, 0, (unsigned long)vec | 0x1UL))
kfree(vec);
else
kmemleak_not_leak(vec);
@@ -2916,6 +2906,12 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
/*
* Returns a pointer to the memory cgroup to which the kernel object is charged.
*
+ * A passed kernel object can be a slab object or a generic kernel page, so
+ * different mechanisms for getting the memory cgroup pointer should be used.
+ * In certain cases (e.g. kernel stacks or large kmallocs with SLUB) the caller
+ * can not know for sure how the kernel object is implemented.
+ * mem_cgroup_from_obj() can be safely used in such cases.
+ *
* The caller must ensure the memcg lifetime, e.g. by taking rcu_read_lock(),
* cgroup_mutex, etc.
*/
@@ -2928,17 +2924,6 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)

page = virt_to_head_page(p);

- /*
- * If page->mem_cgroup is set, it's either a simple mem_cgroup pointer
- * or a pointer to obj_cgroup vector. In the latter case the lowest
- * bit of the pointer is set.
- * The page->mem_cgroup pointer can be asynchronously changed
- * from NULL to (obj_cgroup_vec | 0x1UL), but can't be changed
- * from a valid memcg pointer to objcg vector or back.
- */
- if (!page->mem_cgroup)
- return NULL;
-
/*
* Slab objects are accounted individually, not per-page.
* Memcg membership data for each individual object is saved in
@@ -2956,8 +2941,14 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
return NULL;
}

- /* All other pages use page->mem_cgroup */
- return page->mem_cgroup;
+ /*
+ * page_memcg_check() is used here, because page_has_obj_cgroups()
+ * check above could fail because the object cgroups vector wasn't set
+ * at that moment, but it can be set concurrently.
+ * page_memcg_check(page) will guarantee that a proper memory
+ * cgroup pointer or NULL will be returned.
+ */
+ return page_memcg_check(page);
}

__always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
@@ -3095,7 +3086,7 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
if (memcg && !mem_cgroup_is_root(memcg)) {
ret = __memcg_kmem_charge(memcg, gfp, 1 << order);
if (!ret) {
- page->mem_cgroup = memcg;
+ set_page_memcg(page, memcg);
__SetPageKmemcg(page);
return 0;
}
@@ -3111,7 +3102,7 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
*/
void __memcg_kmem_uncharge_page(struct page *page, int order)
{
- struct mem_cgroup *memcg = page->mem_cgroup;
+ struct mem_cgroup *memcg = page_memcg(page);
unsigned int nr_pages = 1 << order;

if (!memcg)
@@ -3119,7 +3110,7 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)

VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);
__memcg_kmem_uncharge(memcg, nr_pages);
- page->mem_cgroup = NULL;
+ clear_page_memcg(page);
css_put(&memcg->css);

/* slab pages do not have PageKmemcg flag set */
@@ -3270,7 +3261,7 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size)
*/
void mem_cgroup_split_huge_fixup(struct page *head)
{
- struct mem_cgroup *memcg = head->mem_cgroup;
+ struct mem_cgroup *memcg = page_memcg(head);
int i;

if (mem_cgroup_disabled())
@@ -3278,7 +3269,7 @@ void mem_cgroup_split_huge_fixup(struct page *head)

for (i = 1; i < HPAGE_PMD_NR; i++) {
css_get(&memcg->css);
- head[i].mem_cgroup = memcg;
+ set_page_memcg(&head[i], memcg);
}
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -4654,7 +4645,7 @@ void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages,
void mem_cgroup_track_foreign_dirty_slowpath(struct page *page,
struct bdi_writeback *wb)
{
- struct mem_cgroup *memcg = page->mem_cgroup;
+ struct mem_cgroup *memcg = page_memcg(page);
struct memcg_cgwb_frn *frn;
u64 now = get_jiffies_64();
u64 oldest_at = now;
@@ -5623,14 +5614,14 @@ static int mem_cgroup_move_account(struct page *page,

/*
* Prevent mem_cgroup_migrate() from looking at
- * page->mem_cgroup of its source page while we change it.
+ * page's memory cgroup of its source page while we change it.
*/
ret = -EBUSY;
if (!trylock_page(page))
goto out;

ret = -EINVAL;
- if (page->mem_cgroup != from)
+ if (page_memcg(page) != from)
goto out_unlock;

pgdat = page_pgdat(page);
@@ -5685,13 +5676,13 @@ static int mem_cgroup_move_account(struct page *page,
/*
* All state has been migrated, let's switch to the new memcg.
*
- * It is safe to change page->mem_cgroup here because the page
+ * It is safe to change page's memcg here because the page
* is referenced, charged, isolated, and locked: we can't race
* with (un)charging, migration, LRU putback, or anything else
- * that would rely on a stable page->mem_cgroup.
+ * that would rely on a stable page's memory cgroup.
*
* Note that lock_page_memcg is a memcg lock, not a page lock,
- * to save space. As soon as we switch page->mem_cgroup to a
+ * to save space. As soon as we switch page's memory cgroup to a
* new memcg that isn't locked, the above state can change
* concurrently again. Make sure we're truly done with it.
*/
@@ -5700,7 +5691,7 @@ static int mem_cgroup_move_account(struct page *page,
css_get(&to->css);
css_put(&from->css);

- page->mem_cgroup = to;
+ set_page_memcg(page, to);

__unlock_page_memcg(from);

@@ -5766,7 +5757,7 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
* mem_cgroup_move_account() checks the page is valid or
* not under LRU exclusion.
*/
- if (page->mem_cgroup == mc.from) {
+ if (page_memcg(page) == mc.from) {
ret = MC_TARGET_PAGE;
if (is_device_private_page(page))
ret = MC_TARGET_DEVICE;
@@ -5810,7 +5801,7 @@ static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
VM_BUG_ON_PAGE(!page || !PageHead(page), page);
if (!(mc.flags & MOVE_ANON))
return ret;
- if (page->mem_cgroup == mc.from) {
+ if (page_memcg(page) == mc.from) {
ret = MC_TARGET_PAGE;
if (target) {
get_page(page);
@@ -6793,12 +6784,12 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
/*
* Every swap fault against a single page tries to charge the
* page, bail as early as possible. shmem_unuse() encounters
- * already charged pages, too. page->mem_cgroup is protected
- * by the page lock, which serializes swap cache removal, which
- * in turn serializes uncharging.
+ * already charged pages, too. page and memcg binding is
+ * protected by the page lock, which serializes swap cache
+ * removal, which in turn serializes uncharging.
*/
VM_BUG_ON_PAGE(!PageLocked(page), page);
- if (compound_head(page)->mem_cgroup)
+ if (page_memcg(compound_head(page)))
goto out;

id = lookup_swap_cgroup_id(ent);
@@ -6882,21 +6873,21 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)

VM_BUG_ON_PAGE(PageLRU(page), page);

- if (!page->mem_cgroup)
+ if (!page_memcg(page))
return;

/*
* Nobody should be changing or seriously looking at
- * page->mem_cgroup at this point, we have fully
+ * page_memcg(page) at this point, we have fully
* exclusive access to the page.
*/

- if (ug->memcg != page->mem_cgroup) {
+ if (ug->memcg != page_memcg(page)) {
if (ug->memcg) {
uncharge_batch(ug);
uncharge_gather_clear(ug);
}
- ug->memcg = page->mem_cgroup;
+ ug->memcg = page_memcg(page);

/* pairs with css_put in uncharge_batch */
css_get(&ug->memcg->css);
@@ -6913,7 +6904,7 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)
}

ug->dummy_page = page;
- page->mem_cgroup = NULL;
+ clear_page_memcg(page);
css_put(&ug->memcg->css);
}

@@ -6956,7 +6947,7 @@ void mem_cgroup_uncharge(struct page *page)
return;

/* Don't touch page->lru of any random page, pre-check: */
- if (!page->mem_cgroup)
+ if (!page_memcg(page))
return;

uncharge_gather_clear(&ug);
@@ -7006,11 +6997,11 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
return;

/* Page cache replacement: new page already charged? */
- if (newpage->mem_cgroup)
+ if (page_memcg(newpage))
return;

/* Swapcache readahead pages can get replaced before being charged */
- memcg = oldpage->mem_cgroup;
+ memcg = page_memcg(oldpage);
if (!memcg)
return;

@@ -7205,7 +7196,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
return;

- memcg = page->mem_cgroup;
+ memcg = page_memcg(page);

/* Readahead page, never charged */
if (!memcg)
@@ -7226,7 +7217,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
VM_BUG_ON_PAGE(oldid, page);
mod_memcg_state(swap_memcg, MEMCG_SWAP, nr_entries);

- page->mem_cgroup = NULL;
+ clear_page_memcg(page);

if (!mem_cgroup_is_root(memcg))
page_counter_uncharge(&memcg->memory, nr_entries);
@@ -7269,7 +7260,7 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
return 0;

- memcg = page->mem_cgroup;
+ memcg = page_memcg(page);

/* Readahead page, never charged */
if (!memcg)
@@ -7350,7 +7341,7 @@ bool mem_cgroup_swap_full(struct page *page)
if (cgroup_memory_noswap || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
return false;

- memcg = page->mem_cgroup;
+ memcg = page_memcg(page);
if (!memcg)
return false;

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6b1b4a331792..377d65f25d7d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1056,7 +1056,7 @@ static inline bool page_expected_state(struct page *page,
if (unlikely((unsigned long)page->mapping |
page_ref_count(page) |
#ifdef CONFIG_MEMCG
- (unsigned long)page->mem_cgroup |
+ (unsigned long)page_memcg(page) |
#endif
(page->flags & check_flags)))
return false;
@@ -1081,7 +1081,7 @@ static const char *page_bad_reason(struct page *page, unsigned long flags)
bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
}
#ifdef CONFIG_MEMCG
- if (unlikely(page->mem_cgroup))
+ if (unlikely(page_memcg(page)))
bad_reason = "page still charged to cgroup";
#endif
return bad_reason;
diff --git a/mm/page_io.c b/mm/page_io.c
index dc6de6962612..4e12c7bbddcb 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -281,12 +281,14 @@ static inline void count_swpout_vm_event(struct page *page)
static void bio_associate_blkg_from_page(struct bio *bio, struct page *page)
{
struct cgroup_subsys_state *css;
+ struct mem_cgroup *memcg;

- if (!page->mem_cgroup)
+ memcg = page_memcg(page);
+ if (!memcg)
return;

rcu_read_lock();
- css = cgroup_e_css(page->mem_cgroup->css.cgroup, &io_cgrp_subsys);
+ css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
bio_associate_blkg_from_css(bio, css);
rcu_read_unlock();
}
diff --git a/mm/slab.h b/mm/slab.h
index 4a24e1702923..5ac89260f329 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -242,18 +242,17 @@ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t fla
static inline struct obj_cgroup **page_obj_cgroups(struct page *page)
{
/*
- * page->mem_cgroup and page->obj_cgroups are sharing the same
+ * Page's memory cgroup and obj_cgroups vector are sharing the same
* space. To distinguish between them in case we don't know for sure
* that the page is a slab page (e.g. page_cgroup_ino()), let's
* always set the lowest bit of obj_cgroups.
*/
- return (struct obj_cgroup **)
- ((unsigned long)page->obj_cgroups & ~0x1UL);
+ return (struct obj_cgroup **)(page->memcg_data & ~0x1UL);
}

static inline bool page_has_obj_cgroups(struct page *page)
{
- return ((unsigned long)page->obj_cgroups & 0x1UL);
+ return page->memcg_data & 0x1UL;
}

int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
@@ -262,7 +261,7 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
static inline void memcg_free_page_obj_cgroups(struct page *page)
{
kfree(page_obj_cgroups(page));
- page->obj_cgroups = NULL;
+ page->memcg_data = 0;
}

static inline size_t obj_full_size(struct kmem_cache *s)
diff --git a/mm/workingset.c b/mm/workingset.c
index 8ed8e6296d8c..ef563f94a0e3 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -257,7 +257,7 @@ void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg)
struct lruvec *lruvec;
int memcgid;

- /* Page is fully exclusive and pins page->mem_cgroup */
+ /* Page is fully exclusive and pins page's memory cgroup pointer */
VM_BUG_ON_PAGE(PageLRU(page), page);
VM_BUG_ON_PAGE(page_count(page), page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
--
2.26.2