On Tue, Apr 13, 2021 at 09:20:27PM -0400, Waiman Long 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 <[email protected]> > Acked-by: Roman Gushchin <[email protected]> > Reviewed-by: Shakeel Butt <[email protected]> > --- > mm/memcontrol.c | 74 +++++++++++++++++++++++++++++++++++++++---------- > 1 file changed, 59 insertions(+), 15 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 69f728383efe..8875e896e52b 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); \ > + 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(); > } > > @@ -3193,15 +3233,14 @@ 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(); > if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) { > stock->nr_bytes -= nr_bytes; > ret = true; > } > > - local_irq_restore(flags); > + put_obj_stock(flags); > > return ret; > } > @@ -3254,8 +3293,13 @@ static bool obj_stock_flush_required(struct > memcg_stock_pcp *stock, > { > struct mem_cgroup *memcg; > > - if (stock->obj.cached_objcg) { > - memcg = obj_cgroup_memcg(stock->obj.cached_objcg); > + if (in_task() && stock->task_obj.cached_objcg) { > + memcg = obj_cgroup_memcg(stock->task_obj.cached_objcg); > + if (memcg && mem_cgroup_is_descendant(memcg, root_memcg)) > + return true; > + } > + if (stock->irq_obj.cached_objcg) { > + memcg = obj_cgroup_memcg(stock->irq_obj.cached_objcg); > if (memcg && mem_cgroup_is_descendant(memcg, root_memcg)) > return true; > } > @@ -3283,9 +3327,9 @@ static void refill_obj_stock(struct obj_cgroup *objcg, > unsigned int nr_bytes) > { > unsigned long flags; > > - local_irq_save(flags); > + get_obj_stock(flags); > __refill_obj_stock(objcg, nr_bytes); > - local_irq_restore(flags); > + put_obj_stock(flags); > } > > static void __mod_obj_stock_state(struct obj_cgroup *objcg, > @@ -3325,9 +3369,9 @@ void mod_obj_stock_state(struct obj_cgroup *objcg, > struct pglist_data *pgdat, > { > unsigned long flags; > > - local_irq_save(flags); > + get_obj_stock(flags); > __mod_obj_stock_state(objcg, pgdat, idx, nr); > - local_irq_restore(flags); > + put_obj_stock(flags); > } > > int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size) > @@ -3380,10 +3424,10 @@ void obj_cgroup_uncharge_mod_state(struct obj_cgroup > *objcg, size_t size, > { > unsigned long flags; > > - local_irq_save(flags); > + get_obj_stock(flags); > __refill_obj_stock(objcg, size); > __mod_obj_stock_state(objcg, pgdat, idx, -(int)size); > - local_irq_restore(flags); > + put_obj_stock(flags); > } > > #endif /* CONFIG_MEMCG_KMEM */ > -- > 2.18.1 >
Please feel free to add: Tested-by: Masayoshi Mizuma <[email protected]> Thanks! Masa
