memcg: group the cold fields of struct mem_cgroup

These fields are only touched by the cgroup control paths:

  memory_peaks, swap_peaks, peaks_lock   memory.peak open/read/release
  events_file, events_local_file,
  swap_events_file                       cgroup_file_notify()
  cgwb_list, cgwb_domain, cgwb_frn       writeback setup and the
                                         foreign dirty slow path
  mm_list                                MGLRU mm list

They sit in the middle of the struct today.  The three cgroup_file members
alone are 192 bytes of notify state next to the vmstats pointer.  Put them
in one cache line group.

No functional change.

Link: https://lore.kernel.org/20260905030522.1887837-5-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>

1 files changed, 28 insertions, 21 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 66431981f4f7..3a7f80971302 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -228,11 +228,37 @@ struct mem_cgroup {
 
 	__cacheline_group_end_aligned(memcg_write_hot);
 
+	/*
+	 * Off the charge and fault paths.  Not write free: cgwb_domain is
+	 * written on every writeout completion and mm_list on fork, exit and
+	 * MGLRU aging.  They are grouped here so those writes cannot land on
+	 * a line that the fast paths read.
+	 */
+	__cacheline_group_begin_aligned(memcg_cold);
 	/* registered local peak watchers */
 	struct list_head memory_peaks;
 	struct list_head swap_peaks;
 	spinlock_t	 peaks_lock;
 
+	/* memory.events and memory.events.local */
+	struct cgroup_file events_file;
+	struct cgroup_file events_local_file;
+
+	/* handle for "memory.swap.events" */
+	struct cgroup_file swap_events_file;
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+	struct list_head cgwb_list;
+	struct wb_domain cgwb_domain;
+	struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT];
+#endif
+
+#ifdef CONFIG_LRU_GEN_WALKS_MMU
+	/* per-memcg mm_struct list */
+	struct lru_gen_mm_list mm_list;
+#endif
+	__cacheline_group_end_aligned(memcg_cold);
+
 #ifdef CONFIG_ZSWAP
 	unsigned long zswap_max;
 
@@ -248,37 +274,18 @@ struct mem_cgroup {
 	 */
 	bool oom_group;
 
-	/* memory.events and memory.events.local */
-	struct cgroup_file events_file;
-	struct cgroup_file events_local_file;
-
-	/* handle for "memory.swap.events" */
-	struct cgroup_file swap_events_file;
-
 	/* memory.stat */
 	struct memcg_vmstats	*vmstats;
 
 	int kmemcg_id;
 
-#ifdef CONFIG_CGROUP_WRITEBACK
-	struct list_head cgwb_list;
-#endif
-
 	/* Keep the hot per-CPU stats pointer away from memory event counters. */
 	struct memcg_vmstats_percpu __percpu *vmstats_percpu
 		____cacheline_aligned_in_smp;
 
-#ifdef CONFIG_CGROUP_WRITEBACK
-	struct wb_domain cgwb_domain;
-	struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT];
-#endif
-
-#ifdef CONFIG_LRU_GEN_WALKS_MMU
-	/* per-memcg mm_struct list */
-	struct lru_gen_mm_list mm_list;
-#endif
-
 #ifdef CONFIG_MEMCG_V1
+	/* v1 only. Not grouped: v1 is legacy, sorting it is not worth it. */
+
 	/* Legacy consumer-oriented counters */
 	struct page_counter kmem;		/* v1 only */
 	struct page_counter tcpmem;		/* v1 only */