Based on my understanding the optimisation with task_obj for in_task() mask sense on non-PREEMPTIBLE kernels because preempt_disable()/enable() is optimized away. This could be then restricted to !CONFIG_PREEMPTION kernel instead to only PREEMPT_RT. With CONFIG_PREEMPT_DYNAMIC a non-PREEMPTIBLE kernel can also be configured but these kernels always have preempt_disable()/enable() present so it probably makes no sense here for the optimisation. I did a micro benchmark with disabled interrupts and a loop of 100.000.000 invokcations of kfree(kmalloc()). Based on the results it makes no sense to add an exception based on dynamic preemption. Restrict the optimisation to !CONFIG_PREEMPTION kernels. Link: https://lore.kernel.org/all/YdX+INO9gQje6d0S@xxxxxxxxxxxxx Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- mm/memcontrol.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 2d8be88c00888..20ea8f28ad99b 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2030,7 +2030,7 @@ struct memcg_stock_pcp { local_lock_t stock_lock; struct mem_cgroup *cached; /* this never be root cgroup */ unsigned int nr_pages; -#ifndef CONFIG_PREEMPT_RT +#ifndef CONFIG_PREEMPTION /* Protects only task_obj */ local_lock_t task_obj_lock; struct obj_stock task_obj; @@ -2043,7 +2043,7 @@ struct memcg_stock_pcp { }; static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock) = { .stock_lock = INIT_LOCAL_LOCK(stock_lock), -#ifndef CONFIG_PREEMPT_RT +#ifndef CONFIG_PREEMPTION .task_obj_lock = INIT_LOCAL_LOCK(task_obj_lock), #endif }; @@ -2132,7 +2132,7 @@ static void drain_local_stock(struct work_struct *dummy) * drain_stock races is that we always operate on local CPU stock * here with IRQ disabled */ -#ifndef CONFIG_PREEMPT_RT +#ifndef CONFIG_PREEMPTION local_lock(&memcg_stock.task_obj_lock); old = drain_obj_stock(&this_cpu_ptr(&memcg_stock)->task_obj, NULL); local_unlock(&memcg_stock.task_obj_lock); @@ -2741,7 +2741,7 @@ static inline struct obj_stock *get_obj_stock(unsigned long *pflags, { struct memcg_stock_pcp *stock; -#ifndef CONFIG_PREEMPT_RT +#ifndef CONFIG_PREEMPTION if (likely(in_task())) { *pflags = 0UL; *stock_lock_acquried = false; @@ -2759,7 +2759,7 @@ static inline struct obj_stock *get_obj_stock(unsigned long *pflags, static inline void put_obj_stock(unsigned long flags, bool stock_lock_acquried) { -#ifndef CONFIG_PREEMPT_RT +#ifndef CONFIG_PREEMPTION if (likely(!stock_lock_acquried)) { local_unlock(&memcg_stock.task_obj_lock); return; @@ -3177,7 +3177,7 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, { struct mem_cgroup *memcg; -#ifndef CONFIG_PREEMPT_RT +#ifndef CONFIG_PREEMPTION 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)) -- 2.34.1
