On Mon, Apr 12, 2021 at 3:55 PM Waiman Long <[email protected]> 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]>
> ---
> 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.
> if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) {
> @@ -3201,7 +3241,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
> ret = true;
> }
>
> - local_irq_restore(flags);
> + put_obj_stock(flags);
>
> return ret;
> }
> @@ -3254,8 +3294,13 @@ 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 +3328,9 @@ 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 +3370,9 @@ 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 +3425,10 @@ 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
>
On 4/12/21 7:10 PM, Shakeel Butt wrote:
> On Mon, Apr 12, 2021 at 3:55 PM Waiman Long <[email protected]> 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]>
>> ---
>> 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.
Right. I should check the patch carefully. Will remove it.
Thanks,
Longman
On Mon, Apr 12, 2021 at 4:10 PM Shakeel Butt <[email protected]> wrote:
>
> On Mon, Apr 12, 2021 at 3:55 PM Waiman Long <[email protected]> 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]>
> > ---
> > 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 <[email protected]>