The patch titled
Subject: fs: buffer: use raw page_memcg() on locked page
has been added to the -mm tree. Its filename is
fs-buffer-use-raw-page_memcg-on-locked-page.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/fs-buffer-use-raw-page_memcg-on-locked-page.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/fs-buffer-use-raw-page_memcg-on-locked-page.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: fs: buffer: use raw page_memcg() on locked page
alloc_page_buffers() currently uses get_mem_cgroup_from_page() for
charging the buffers to the page owner, which does an rcu-protected
page->memcg lookup and acquires a reference. But buffer allocation has
the page lock held throughout, which pins the page to the memcg and
thereby the memcg - neither rcu nor holding an extra reference during the
allocation are necessary. Use a raw page_memcg() instead.
This was the last user of get_mem_cgroup_from_page(), delete it.
Link: https://lkml.kernel.org/r/20210209190126.97842-1-hannes@xxxxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reported-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/buffer.c | 4 ++--
include/linux/memcontrol.h | 7 -------
mm/memcontrol.c | 23 -----------------------
3 files changed, 2 insertions(+), 32 deletions(-)
--- a/fs/buffer.c~fs-buffer-use-raw-page_memcg-on-locked-page
+++ a/fs/buffer.c
@@ -847,7 +847,8 @@ struct buffer_head *alloc_page_buffers(s
if (retry)
gfp |= __GFP_NOFAIL;
- memcg = get_mem_cgroup_from_page(page);
+ /* The page lock pins the memcg */
+ memcg = page_memcg(page);
old_memcg = set_active_memcg(memcg);
head = NULL;
@@ -868,7 +869,6 @@ struct buffer_head *alloc_page_buffers(s
}
out:
set_active_memcg(old_memcg);
- mem_cgroup_put(memcg);
return head;
/*
* In case anything failed, we just free everything we got.
--- a/include/linux/memcontrol.h~fs-buffer-use-raw-page_memcg-on-locked-page
+++ a/include/linux/memcontrol.h
@@ -680,8 +680,6 @@ struct mem_cgroup *mem_cgroup_from_task(
struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
-struct mem_cgroup *get_mem_cgroup_from_page(struct page *page);
-
struct lruvec *lock_page_lruvec(struct page *page);
struct lruvec *lock_page_lruvec_irq(struct page *page);
struct lruvec *lock_page_lruvec_irqsave(struct page *page,
@@ -1190,11 +1188,6 @@ static inline struct mem_cgroup *get_mem
{
return NULL;
}
-
-static inline struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)
-{
- return NULL;
-}
static inline void mem_cgroup_put(struct mem_cgroup *memcg)
{
--- a/mm/memcontrol.c~fs-buffer-use-raw-page_memcg-on-locked-page
+++ a/mm/memcontrol.c
@@ -1047,29 +1047,6 @@ struct mem_cgroup *get_mem_cgroup_from_m
}
EXPORT_SYMBOL(get_mem_cgroup_from_mm);
-/**
- * get_mem_cgroup_from_page: Obtain a reference on given page's memcg.
- * @page: page from which memcg should be extracted.
- *
- * Obtain a reference on page->memcg and returns it if successful. Otherwise
- * root_mem_cgroup is returned.
- */
-struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)
-{
- struct mem_cgroup *memcg = page_memcg(page);
-
- if (mem_cgroup_disabled())
- return NULL;
-
- rcu_read_lock();
- /* Page should not get uncharged and freed memcg under us. */
- if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css)))
- memcg = root_mem_cgroup;
- rcu_read_unlock();
- return memcg;
-}
-EXPORT_SYMBOL(get_mem_cgroup_from_page);
-
static __always_inline struct mem_cgroup *active_memcg(void)
{
if (in_interrupt())
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
revert-mm-memcontrol-avoid-workload-stalls-when-lowering-memoryhigh.patch
fs-buffer-use-raw-page_memcg-on-locked-page.patch
mm-vmstat-fix-nohz-wakeups-for-node-stat-changes.patch
mm-vmstat-add-some-comments-on-internal-storage-of-byte-items.patch
