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memcg: add nmi-safe update for MEMCG_KMEM

The objcg based kmem charging and uncharging code path needs to update
MEMCG_KMEM appropriately. Let's add support to update MEMCG_KMEM in
nmi-safe way for those code paths.

Link: https://lkml.kernel.org/r/20250519063142.111219-4-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

authored by

Shakeel Butt and committed by
Andrew Morton 9d3edf96 940b01fc

+19 -2
+19 -2
mm/memcontrol.c
··· 2715 2715 return objcg; 2716 2716 } 2717 2717 2718 + #ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC 2719 + static inline void account_kmem_nmi_safe(struct mem_cgroup *memcg, int val) 2720 + { 2721 + if (likely(!in_nmi())) { 2722 + mod_memcg_state(memcg, MEMCG_KMEM, val); 2723 + } else { 2724 + /* TODO: add to cgroup update tree once it is nmi-safe. */ 2725 + atomic_add(val, &memcg->kmem_stat); 2726 + } 2727 + } 2728 + #else 2729 + static inline void account_kmem_nmi_safe(struct mem_cgroup *memcg, int val) 2730 + { 2731 + mod_memcg_state(memcg, MEMCG_KMEM, val); 2732 + } 2733 + #endif 2734 + 2718 2735 /* 2719 2736 * obj_cgroup_uncharge_pages: uncharge a number of kernel pages from a objcg 2720 2737 * @objcg: object cgroup to uncharge ··· 2744 2727 2745 2728 memcg = get_mem_cgroup_from_objcg(objcg); 2746 2729 2747 - mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages); 2730 + account_kmem_nmi_safe(memcg, -nr_pages); 2748 2731 memcg1_account_kmem(memcg, -nr_pages); 2749 2732 if (!mem_cgroup_is_root(memcg)) 2750 2733 refill_stock(memcg, nr_pages); ··· 2772 2755 if (ret) 2773 2756 goto out; 2774 2757 2775 - mod_memcg_state(memcg, MEMCG_KMEM, nr_pages); 2758 + account_kmem_nmi_safe(memcg, nr_pages); 2776 2759 memcg1_account_kmem(memcg, nr_pages); 2777 2760 out: 2778 2761 css_put(&memcg->css);