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> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Acked-by: Roman Gushchin <guro@xxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> 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()) _
