On Tue 09-02-21 14:01:26, Johannes Weiner wrote: > 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. > > Reported-by: Muchun Song <[email protected]> > Signed-off-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]> Thanks! > --- > fs/buffer.c | 4 ++-- > include/linux/memcontrol.h | 7 ------- > mm/memcontrol.c | 23 ----------------------- > 3 files changed, 2 insertions(+), 32 deletions(-) > > diff --git a/fs/buffer.c b/fs/buffer.c > index 96c7604f69b3..dc5d3e22c493 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -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. > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index a8c7a0ccc759..a44b2d51aecc 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -687,8 +687,6 @@ 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, > @@ -1169,11 +1167,6 @@ 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) > { > } > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 51778fa9b462..9e455815fb7a 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1048,29 +1048,6 @@ 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()) > -- > 2.30.0 -- Michal Hocko SUSE Labs
