+ memcg-simplify-high-limit-handling-after-a-charge.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: memcg: simplify high limit handling after a charge
has been added to the -mm mm-new branch.  Its filename is
     memcg-simplify-high-limit-handling-after-a-charge.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-simplify-high-limit-handling-after-a-charge.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Shakeel Butt <shakeel.butt@linux.dev>
Subject: memcg: simplify high limit handling after a charge
Date: Fri, 30 Oct 2026 13:54:16 -0700

Separate the hierarchy scan from high-limit enforcement. Find the first
cgroup over the applicable limit, then queue high_work or record the
task's overage after the scan. Worker contexts check only memory.high;
local charges also check memory.swap.high.

Clarify the enforcement comments. Keep the synchronous pending-overage
check independent of the scan result so a blocking charge still handles
overage left by earlier charges.

No functional change intended.

Link: https://lore.kernel.org/20261030205418.341214-6-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
---

 mm/memcontrol.c |  102 ++++++++++++++++++++--------------------------
 1 file changed, 45 insertions(+), 57 deletions(-)

--- a/mm/memcontrol.c~memcg-simplify-high-limit-handling-after-a-charge
+++ a/mm/memcontrol.c
@@ -2611,9 +2611,8 @@ static unsigned long calculate_high_dela
 }
 
 /*
- * Reclaims memory over the high limit. Called directly from
- * try_charge() (context permitting), as well as from the userland
- * return path where reclaim is always able to block.
+ * Handle pending high overage during a blocking charge or on return
+ * to userspace.
  */
 void __mem_cgroup_handle_over_high(gfp_t gfp_mask)
 {
@@ -2707,76 +2706,65 @@ out:
 
 /*
  * Called after @nr_pages were charged to @memcg. If @memcg or one of its
- * ancestors is over memory.high or memory.swap.high, start reclaim or slow
- * down the task.
+ * ancestors is over its high limit, either queue high_work to reclaim from
+ * that cgroup, or record the overage so the charging task reclaims later
+ * and sleeps if reclaim can't keep up. high_work only handles memory.high;
+ * memory.swap.high is only enforced on the charging task.
  */
 static void memcg_enforce_high(struct mem_cgroup *memcg, unsigned int nr_pages,
 			       gfp_t gfp_mask)
 {
+	struct mem_cgroup *iter;
 	bool allow_spinning = gfpflags_allow_spinning(gfp_mask);
-	bool use_worker = !in_task() || (current->flags & PF_KTHREAD) ||
+	bool use_high_work = !in_task() || (current->flags & PF_KTHREAD) ||
 		!current->mm || !mm_match_cgroup(current->mm, memcg);
 
 	/*
-	 * If the hierarchy is above the normal consumption range, schedule
-	 * reclaim on returning to userland.  We can perform reclaim here
-	 * if __GFP_RECLAIM but let's always punt for simplicity and so that
-	 * GFP_KERNEL can consistently be used during reclaim.  @memcg is
-	 * not recorded as it most likely matches current's and won't
-	 * change in the meantime.  As high limit is checked again before
-	 * reclaim, the cost of mismatch is negligible.
+	 * Check the charged cgroup and its parents. Local charges normally defer
+	 * reclaim until return to userspace so it can use GFP_KERNEL. Large
+	 * pending overages may be handled synchronously below. The handler looks
+	 * up current->mm and rechecks the limits. If the task moved to another
+	 * cgroup in the meantime, the handler works on the new cgroup instead.
+	 * That is rare and costs little.
 	 */
-	do {
+	for (iter = memcg; iter; iter = parent_mem_cgroup(iter)) {
 		bool mem_high, swap_high;
 
-		mem_high = page_counter_read(&memcg->memory) >
-			READ_ONCE(memcg->memory.high);
-		swap_high = page_counter_read(&memcg->swap) >
-			READ_ONCE(memcg->swap.high);
-
-		/*
-		 * Don't make an unrelated interrupted task handle this charge.
-		 * Kernel threads may be working for other tasks, so let a worker
-		 * reclaim instead.
-		 * Remote charges need reclaim from their charged hierarchy.
-		 */
-		if (use_worker) {
-			if (mem_high) {
-				if (allow_spinning)
-					schedule_work(&memcg->high_work);
-				else
-					irq_work_queue(&memcg->high_irq_work);
-				break;
-			}
-			continue;
-		}
-
-		if (mem_high || swap_high) {
-			/*
-			 * The allocating tasks in this cgroup will need to do
-			 * reclaim or be throttled to prevent further growth
-			 * of the memory or swap footprints.
-			 *
-			 * Target some best-effort fairness between the tasks,
-			 * and distribute reclaim work and delay penalties
-			 * based on how much each task is actually allocating.
-			 */
-			current->memcg_nr_pages_over_high += nr_pages;
-			set_notify_resume(current);
+		mem_high = page_counter_read(&iter->memory) >
+			READ_ONCE(iter->memory.high);
+		swap_high = !use_high_work &&
+			(page_counter_read(&iter->swap) > READ_ONCE(iter->swap.high));
+		if (mem_high || swap_high)
 			break;
-		}
-	} while ((memcg = parent_mem_cgroup(memcg)));
+	}
 
-	/* Interrupts, kernel threads, and remote chargers stop here. */
-	if (use_worker)
+	/*
+	 * Use a worker for interrupts, kernel threads, and tasks whose mm
+	 * does not match the charged hierarchy.
+	 */
+	if (use_high_work) {
+		if (!iter)
+			return;
+		if (allow_spinning)
+			schedule_work(&iter->high_work);
+		else
+			irq_work_queue(&iter->high_irq_work);
 		return;
+	}
+
+	if (iter) {
+		/*
+		 * Count the full batch so reclaim work and delay penalties scale
+		 * with the pages charged by this task.
+		 */
+		current->memcg_nr_pages_over_high += nr_pages;
+		set_notify_resume(current);
+	}
 
 	/*
-	 * Reclaim is set up above to be called from the userland
-	 * return path. But also attempt synchronous reclaim to avoid
-	 * excessive overrun while the task is still inside the
-	 * kernel. If this is successful, the return path will see it
-	 * when it rechecks the overage and simply bail out.
+	 * Earlier charges may have left high overage pending even if this charge
+	 * found no new overage. Handle it now if this charge can block, to limit
+	 * overrun while the task remains in the kernel.
 	 */
 	if (current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH &&
 	    gfpflags_allow_blocking(gfp_mask))
_

Patches currently in -mm which might be from shakeel.butt@linux.dev are

memcg-move-memoryhigh-enforcement-out-of-try_charge_memcg.patch
memcg-force-charges-from-reclaim-before-trying-the-limits.patch
memcg-use-high_work-for-kernel-threads.patch
memcg-use-high_work-for-remote-charges.patch
memcg-simplify-high-limit-handling-after-a-charge.patch