[PATCH rfc 5/5] mm: convert page kmemcg type to a page memcg flag
From: Roman Gushchin
Date: Thu Sep 10 2020 - 16:47:49 EST
PageKmemcg flag is currently defined as a page type (like buddy,
offline, table and guard). Semantically it means that the page
was accounted as a kernel memory by the page allocator and has
to be uncharged on the release.
As a side effect of defining the flag as a page type, the accounted
page can't be mapped to userspace (look at page_has_type() and
comments above). In particular, this blocks the accounting of
vmalloc-backed memory used by some bpf maps, because these maps
do map the memory to userspace.
One option is to fix it by complicating the access to page->mapcount,
which provides some free bits for page->page_type.
But it's way better to move this flag into page->memcg_data flags.
Indeed, the flag makes no sense without enabled memory cgroups
and memory cgroup pointer set in particular.
This commit replaces PageKmemcg() and __SetPageKmemcg() with
PageMemcgKmem() and SetPageMemcgKmem(). __ClearPageKmemcg()
can be simple deleted because clear_page_mem_cgroup() already
does the job.
As a bonus, on !CONFIG_MEMCG build the PageMemcgKmem() check will
be compiled out.
Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
include/linux/memcontrol.h | 35 ++++++++++++++++++++++++++++++++---
include/linux/page-flags.h | 11 ++---------
mm/memcontrol.c | 14 ++++----------
mm/page_alloc.c | 2 +-
4 files changed, 39 insertions(+), 23 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7ab5f92bb686..430d1ca925c9 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -343,15 +343,22 @@ extern struct mem_cgroup *root_mem_cgroup;
enum page_memcg_flags {
/* page->memcg_data is a pointer to a objcgs vector */
PG_MEMCG_OBJ_CGROUPS,
+ /* page has been accounted as a non-slab kernel page */
+ PG_MEMCG_KMEM,
+ /* the next bit after the last actual flag */
+ PG_MEMCG_LAST_FLAG,
};
+#define MEMCG_FLAGS_MASK ((1UL << PG_MEMCG_LAST_FLAG) - 1)
+
static inline struct mem_cgroup *page_mem_cgroup(struct page *page)
{
unsigned long memcg_data = page->memcg_data;
VM_BUG_ON_PAGE(PageSlab(page), page);
+ VM_BUG_ON_PAGE(test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data), page);
- return (struct mem_cgroup *)memcg_data;
+ return (struct mem_cgroup *)(memcg_data & ~MEMCG_FLAGS_MASK);
}
static inline struct mem_cgroup *page_mem_cgroup_check(struct page *page)
@@ -361,7 +368,7 @@ static inline struct mem_cgroup *page_mem_cgroup_check(struct page *page)
if (test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data))
return NULL;
- return (struct mem_cgroup *)memcg_data;
+ return (struct mem_cgroup *)(memcg_data & ~MEMCG_FLAGS_MASK);
}
static inline void set_page_mem_cgroup(struct page *page,
@@ -377,6 +384,16 @@ static inline void clear_page_mem_cgroup(struct page *page)
page->memcg_data = 0;
}
+static inline bool PageMemcgKmem(struct page *page)
+{
+ return test_bit(PG_MEMCG_KMEM, &page->memcg_data);
+}
+
+static inline void SetPageMemcgKmem(struct page *page)
+{
+ __set_bit(PG_MEMCG_KMEM, &page->memcg_data);
+}
+
#ifdef CONFIG_MEMCG_KMEM
static inline struct obj_cgroup **page_obj_cgroups(struct page *page)
{
@@ -385,6 +402,7 @@ static inline struct obj_cgroup **page_obj_cgroups(struct page *page)
VM_BUG_ON_PAGE(memcg_data && !test_bit(PG_MEMCG_OBJ_CGROUPS,
&memcg_data), page);
__clear_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data);
+ VM_BUG_ON_PAGE(test_bit(PG_MEMCG_KMEM, &memcg_data), page);
return (struct obj_cgroup **)memcg_data;
}
@@ -393,8 +411,10 @@ static inline struct obj_cgroup **page_obj_cgroups_check(struct page *page)
{
unsigned long memcg_data = page->memcg_data;
- if (memcg_data && test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data))
+ if (memcg_data && test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data)) {
+ VM_BUG_ON_PAGE(test_bit(PG_MEMCG_KMEM, &memcg_data), page);
return (struct obj_cgroup **)memcg_data;
+ }
return NULL;
}
@@ -1052,6 +1072,15 @@ static inline void clear_page_mem_cgroup(struct page *page)
{
}
+static inline bool PageMemcgKmem(struct page *page)
+{
+ return false;
+}
+
+static inline void SetPageMemcgKmem(struct page *page)
+{
+}
+
static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
{
return true;
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index fbbb841a9346..a7ca01ae78d9 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -712,9 +712,8 @@ PAGEFLAG_FALSE(DoubleMap)
#define PAGE_MAPCOUNT_RESERVE -128
#define PG_buddy 0x00000080
#define PG_offline 0x00000100
-#define PG_kmemcg 0x00000200
-#define PG_table 0x00000400
-#define PG_guard 0x00000800
+#define PG_table 0x00000200
+#define PG_guard 0x00000400
#define PageType(page, flag) \
((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
@@ -765,12 +764,6 @@ PAGE_TYPE_OPS(Buddy, buddy)
*/
PAGE_TYPE_OPS(Offline, offline)
-/*
- * If kmemcg is enabled, the buddy allocator will set PageKmemcg() on
- * pages allocated with __GFP_ACCOUNT. It gets cleared on page free.
- */
-PAGE_TYPE_OPS(Kmemcg, kmemcg)
-
/*
* Marks pages in use as page tables.
*/
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ba9b053b1b88..d4c21870dab9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3070,7 +3070,7 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
ret = __memcg_kmem_charge(memcg, gfp, 1 << order);
if (!ret) {
set_page_mem_cgroup(page, memcg);
- __SetPageKmemcg(page);
+ SetPageMemcgKmem(page);
return 0;
}
css_put(&memcg->css);
@@ -3095,10 +3095,6 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
__memcg_kmem_uncharge(memcg, nr_pages);
clear_page_mem_cgroup(page);
css_put(&memcg->css);
-
- /* slab pages do not have PageKmemcg flag set */
- if (PageKmemcg(page))
- __ClearPageKmemcg(page);
}
static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
@@ -6830,12 +6826,10 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)
nr_pages = compound_nr(page);
ug->nr_pages += nr_pages;
- if (!PageKmemcg(page)) {
- ug->pgpgout++;
- } else {
+ if (PageMemcgKmem(page))
ug->nr_kmem += nr_pages;
- __ClearPageKmemcg(page);
- }
+ else
+ ug->pgpgout++;
ug->dummy_page = page;
clear_page_mem_cgroup(page);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a707671f3b6c..3a61868113ec 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1197,7 +1197,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
}
if (PageMappingFlags(page))
page->mapping = NULL;
- if (memcg_kmem_enabled() && PageKmemcg(page))
+ if (memcg_kmem_enabled() && PageMemcgKmem(page))
__memcg_kmem_uncharge_page(page, order);
if (check_free)
bad += check_free_page(page);
--
2.26.2