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memcg-int16_t-for-cached-slab-stats.patch removed from -mm tree

merged mm-stable Andrew Morton 1 participant 1 message Jun 2

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The quilt patch titled
Subject: memcg: int16_t for cached slab stats
has been removed from the -mm tree. Its filename was
memcg-int16_t-for-cached-slab-stats.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Shakeel Butt <[email protected]>
Subject: memcg: int16_t for cached slab stats
Date: Mon, 25 May 2026 20:39:30 -0700

Currently struct obj_stock_pcp stores cached slab stats in 'int' which is 4 bytes per counter on 64-bit machines. Switch them to int16_t to shrink the cached metadata.

The existing PAGE_SIZE flush in __account_obj_stock() bounds *bytes at PAGE_SIZE on 4KiB and 16KiB page archs, well within int16_t. On 64KiB pages PAGE_SIZE is well above S16_MAX so that flush never fires, and a sufficiently long run of accumulations would overflow the cache. Add an explicit S16_MAX guard before each add: when the next add would push abs(*bytes) past S16_MAX, fold the cached value into @nr and flush directly via mod_objcg_mlstate() before the accumulation.

Link https://lore.kernel.org/[email protected] open here
Fixes 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type")
Signed-off-by Shakeel Butt <[email protected]>
Tested-by kernel test robot <[email protected]>
Reviewed-by Harry Yoo (Oracle) <[email protected]>
Acked-by Qi Zheng <[email protected]>
Acked-by Muchun Song <[email protected]>
Cc Alexandre Ghiti <[email protected]>
Cc Johannes Weiner <[email protected]>
Cc Joshua Hahn <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Roman Gushchin <[email protected]>
Signed-off-by Andrew Morton <[email protected]>

---

 mm/memcontrol.c |   25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)
mm/memcontrol.c renamed from mm/memcontrol.c~memcg-int16_t-for-cached-slab-stats +12 -13
@@ -2032,8 +2032,8 @@ struct obj_stock_pcp {
 	uint16_t nr_bytes;
 #endif
 	int16_t node_id;
-	int nr_slab_reclaimable_b;
-	int nr_slab_unreclaimable_b;
+	int16_t nr_slab_reclaimable_b;
+	int16_t nr_slab_unreclaimable_b;
 
 	struct work_struct work;
 	unsigned long flags;

@@ -3170,7 +3170,7 @@ static void __account_obj_stock(struct o
 				struct obj_stock_pcp *stock, int nr,
 				struct pglist_data *pgdat, enum node_stat_item idx)
 {
-	int *bytes;
+	int16_t *bytes;
 
 	/*
 	 * Though at the moment MAX_NUMNODES <= 1024 in all archs but let's make

@@ -3207,21 +3207,20 @@ static void __account_obj_stock(struct o
 
 	bytes = (idx == NR_SLAB_RECLAIMABLE_B) ? &stock->nr_slab_reclaimable_b
 					       : &stock->nr_slab_unreclaimable_b;
+
 	/*
-	 * Even for large object >= PAGE_SIZE, the vmstat data will still be
-	 * cached locally at least once before pushing it out.
+	 * Fold @nr into the cached value and decide whether to keep it cached
+	 * or flush it directly. Cache the combined value when it fits in the
+	 * int16_t storage and either the cache was empty (so even a value
+	 * above PAGE_SIZE gets a chance to be canceled by a paired delta) or
+	 * the combined value is within the PAGE_SIZE flush threshold.
 	 */
-	if (!*bytes) {
+	nr += *bytes;
+	if (abs(nr) <= S16_MAX && (!*bytes || abs(nr) <= PAGE_SIZE)) {
 		*bytes = nr;
 		nr = 0;
 	} else {
-		*bytes += nr;
-		if (abs(*bytes) > PAGE_SIZE) {
-			nr = *bytes;
-			*bytes = 0;
-		} else {
-			nr = 0;
-		}
+		*bytes = 0;
 	}
 direct:
 	if (nr)

_

Patches currently in -mm which might be from [email protected] are

mm-list_lru-drain-before-clearing-xarray-entry-on-reparent.patch