Re: [PATCH RFC] mm: Add function for testing if the current lruvec lock is valid

Alex Shi
2020-07-31T23:54:48Z

It looks much better than mine. and could replace 'mm/lru: introduce the relock_page_lruvec function'
with your author signed. :)

BTW,
it's the rcu_read_lock cause the will-it-scale/page_fault3 regression which you mentained in another
letter?

Thanks
Alex

在 2020/8/1 上午5:14, alexander.h.duyck-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org 写道:
> From: Alexander Duyck <alexander.h.duyck-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
>
> When testing for relock we can avoid the need for RCU locking if we simply
> compare the page pgdat and memcg pointers versus those that the lruvec is
> holding. By doing this we can avoid the extra pointer walks and accesses of
> the memory cgroup.
>
> In addition we can avoid the checks entirely if lruvec is currently NULL.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> ---
> include/linux/memcontrol.h | 52 +++++++++++++++++++++++++++-----------------
> 1 file changed, 32 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 6e670f991b42..7a02f00bf3de 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -405,6 +405,22 @@ static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg,
>
> struct lruvec *mem_cgroup_page_lruvec(struct page *, struct pglist_data *);
>
> +static inline bool lruvec_holds_page_lru_lock(struct page *page,
> + struct lruvec *lruvec)
> +{
> + pg_data_t *pgdat = page_pgdat(page);
> + const struct mem_cgroup *memcg;
> + struct mem_cgroup_per_node *mz;
> +
> + if (mem_cgroup_disabled())
> + return lruvec == &pgdat->__lruvec;
> +
> + mz = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> + memcg = page->mem_cgroup ? : root_mem_cgroup;
> +
> + return lruvec->pgdat == pgdat && mz->memcg == memcg;
> +}
> +
> struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
>
> struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
> @@ -880,6 +896,14 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page,
> return &pgdat->__lruvec;
> }
>
> +static inline bool lruvec_holds_page_lru_lock(struct page *page,
> + struct lruvec *lruvec)
> +{
> + pg_data_t *pgdat = page_pgdat(page);
> +
> + return lruvec == &pgdat->__lruvec;
> +}
> +
> static inline struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg)
> {
> return NULL;
> @@ -1317,18 +1341,12 @@ static inline void unlock_page_lruvec_irqrestore(struct lruvec *lruvec,
> static inline struct lruvec *relock_page_lruvec_irq(struct page *page,
> struct lruvec *locked_lruvec)
> {
> - struct pglist_data *pgdat = page_pgdat(page);
> - bool locked;
> + if (locked_lruvec) {
> + if (lruvec_holds_page_lru_lock(page, locked_lruvec))
> + return locked_lruvec;
>
> - rcu_read_lock();
> - locked = mem_cgroup_page_lruvec(page, pgdat) == locked_lruvec;
> - rcu_read_unlock();
> -
> - if (locked)
> - return locked_lruvec;
> -
> - if (locked_lruvec)
> unlock_page_lruvec_irq(locked_lruvec);
> + }
>
> return lock_page_lruvec_irq(page);
> }
> @@ -1337,18 +1355,12 @@ static inline struct lruvec *relock_page_lruvec_irq(struct page *page,
> static inline struct lruvec *relock_page_lruvec_irqsave(struct page *page,
> struct lruvec *locked_lruvec, unsigned long *flags)
> {
> - struct pglist_data *pgdat = page_pgdat(page);
> - bool locked;
> -
> - rcu_read_lock();
> - locked = mem_cgroup_page_lruvec(page, pgdat) == locked_lruvec;
> - rcu_read_unlock();
> -
> - if (locked)
> - return locked_lruvec;
> + if (locked_lruvec) {
> + if (lruvec_holds_page_lru_lock(page, locked_lruvec))
> + return locked_lruvec;
>
> - if (locked_lruvec)
> unlock_page_lruvec_irqrestore(locked_lruvec, *flags);
> + }
>
> return lock_page_lruvec_irqsave(page, flags);
> }
>