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Message-ID: <CALvZod4CUMOBOkC8NjXXJ_qu3kvhcw+zrux+c516BMcAuHTcuA@mail.gmail.com>
Date: Mon, 12 Apr 2021 16:14:10 -0700
From: Shakeel Butt <shakeelb@...gle.com>
To: Waiman Long <longman@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Vladimir Davydov <vdavydov.dev@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <guro@...com>,
LKML <linux-kernel@...r.kernel.org>,
Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
Muchun Song <songmuchun@...edance.com>,
Alex Shi <alex.shi@...ux.alibaba.com>,
Chris Down <chris@...isdown.name>,
Yafang Shao <laoar.shao@...il.com>,
Wei Yang <richard.weiyang@...il.com>,
Masayoshi Mizuma <msys.mizuma@...il.com>,
Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Subject: Re: [PATCH v2 5/5] mm/memcg: Optimize user context object stock access
On Mon, Apr 12, 2021 at 4:10 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Mon, Apr 12, 2021 at 3:55 PM Waiman Long <longman@...hat.com> wrote:
> >
> > Most kmem_cache_alloc() calls are from user context. With instrumentation
> > enabled, the measured amount of kmem_cache_alloc() calls from non-task
> > context was about 0.01% of the total.
> >
> > The irq disable/enable sequence used in this case to access content
> > from object stock is slow. To optimize for user context access, there
> > are now two object stocks for task context and interrupt context access
> > respectively.
> >
> > The task context object stock can be accessed after disabling preemption
> > which is cheap in non-preempt kernel. The interrupt context object stock
> > can only be accessed after disabling interrupt. User context code can
> > access interrupt object stock, but not vice versa.
> >
> > The mod_objcg_state() function is also modified to make sure that memcg
> > and lruvec stat updates are done with interrupted disabled.
> >
> > The downside of this change is that there are more data stored in local
> > object stocks and not reflected in the charge counter and the vmstat
> > arrays. However, this is a small price to pay for better performance.
> >
> > Signed-off-by: Waiman Long <longman@...hat.com>
> > Acked-by: Roman Gushchin <guro@...com>
> > ---
> > mm/memcontrol.c | 73 +++++++++++++++++++++++++++++++++++++++----------
> > 1 file changed, 59 insertions(+), 14 deletions(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 69f728383efe..29f2df76644a 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -2229,7 +2229,8 @@ struct obj_stock {
> > struct memcg_stock_pcp {
> > struct mem_cgroup *cached; /* this never be root cgroup */
> > unsigned int nr_pages;
> > - struct obj_stock obj;
> > + struct obj_stock task_obj;
> > + struct obj_stock irq_obj;
> >
> > struct work_struct work;
> > unsigned long flags;
> > @@ -2254,11 +2255,48 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
> > }
> > #endif
> >
> > +/*
> > + * Most kmem_cache_alloc() calls are from user context. The irq disable/enable
> > + * sequence used in this case to access content from object stock is slow.
> > + * To optimize for user context access, there are now two object stocks for
> > + * task context and interrupt context access respectively.
> > + *
> > + * The task context object stock can be accessed by disabling preemption only
> > + * which is cheap in non-preempt kernel. The interrupt context object stock
> > + * can only be accessed after disabling interrupt. User context code can
> > + * access interrupt object stock, but not vice versa.
> > + */
> > static inline struct obj_stock *current_obj_stock(void)
> > {
> > struct memcg_stock_pcp *stock = this_cpu_ptr(&memcg_stock);
> >
> > - return &stock->obj;
> > + return in_task() ? &stock->task_obj : &stock->irq_obj;
> > +}
> > +
> > +#define get_obj_stock(flags) \
> > +({ \
> > + struct memcg_stock_pcp *stock; \
> > + struct obj_stock *obj_stock; \
> > + \
> > + if (in_task()) { \
> > + preempt_disable(); \
> > + (flags) = -1L; \
> > + stock = this_cpu_ptr(&memcg_stock); \
>
> The above line was missing in the previous version.
>
> > + obj_stock = &stock->task_obj; \
> > + } else { \
> > + local_irq_save(flags); \
> > + stock = this_cpu_ptr(&memcg_stock); \
> > + obj_stock = &stock->irq_obj; \
> > + } \
> > + obj_stock; \
> > +})
> > +
> > +static inline void put_obj_stock(unsigned long flags)
> > +{
> > + if (flags == -1L)
> > + preempt_enable();
> > + else
> > + local_irq_restore(flags);
> > }
> >
> > /**
> > @@ -2327,7 +2365,9 @@ static void drain_local_stock(struct work_struct *dummy)
> > local_irq_save(flags);
> >
> > stock = this_cpu_ptr(&memcg_stock);
> > - drain_obj_stock(&stock->obj);
> > + drain_obj_stock(&stock->irq_obj);
> > + if (in_task())
> > + drain_obj_stock(&stock->task_obj);
> > drain_stock(stock);
> > clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
> >
> > @@ -3183,7 +3223,7 @@ static inline void mod_objcg_state(struct obj_cgroup *objcg,
> > memcg = obj_cgroup_memcg(objcg);
> > if (pgdat)
> > lruvec = mem_cgroup_lruvec(memcg, pgdat);
> > - __mod_memcg_lruvec_state(memcg, lruvec, idx, nr);
> > + mod_memcg_lruvec_state(memcg, lruvec, idx, nr);
> > rcu_read_unlock();
> > }
> >
> > @@ -3193,7 +3233,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
> > unsigned long flags;
> > bool ret = false;
> >
> > - local_irq_save(flags);
> > + stock = get_obj_stock(flags);
> >
> > stock = current_obj_stock();
>
> The above is redundant.
>
After cleanup you can add:
Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
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