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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@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2021-02-24 12:04:15 -08:00 committed by Linus Torvalds
parent a7b7e1df89
commit 6eeb104e11
3 changed files with 2 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
fs/buffer.c
View File

@ -847,7 +847,8 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
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(struct page *page, unsigned long size,
}
out:
set_active_memcg(old_memcg);
mem_cgroup_put(memcg);
return head;
/*
* In case anything failed, we just free everything we got.

7
include/linux/memcontrol.h
View File

@ -680,8 +680,6 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
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,
@ -1191,11 +1189,6 @@ static inline struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
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)
{
}

23
mm/memcontrol.c
View File

@ -1047,29 +1047,6 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
}
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())