[merged mm-stable] mm-percpu-account-full-object-size-for-percpu-memory-allocations.patch removed from -mm tree

[merged mm-stable] mm-percpu-account-full-object-size-for-percpu-memory-allocations.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/percpu: account full object size for percpu memory allocations
has been removed from the -mm tree.  Its filename was
     mm-percpu-account-full-object-size-for-percpu-memory-allocations.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: "Harry Yoo (Meta)" <harry@kernel.org>
Subject: mm/percpu: account full object size for percpu memory allocations
Date: Tue, 13 Oct 2026 20:34:39 +0100

When memory allocation profiling is enabled, the pages backing percpu
memory chunks are attributed to func:pcpu_alloc_pages.  However, the
accounting of individual percpu memory allocations via alloc_percpu()
and friends record only the size of a single object rather than its
full size across all CPUs.

As a result, it is often not straightforward to identify which kernel code
is actually responsible for percpu memory, because the size is
under-accounted by a factor of num_possible_cpus().

Account full object size with pcpu_obj_full_size(size) instead, which
multiplies the object size by num_possible_cpus() and adds the objcg
pointer overhead.  This is consistent with what memcg already does for
charging percpu allocations.

Verified with 64-CPU VM by spawning 400 processes in a memory cgroup and
measuring mm_init()'s rss_stat counters.

Delta of kernel/fork.c:1142 func:mm_init in /proc/allocinfo:

                  bytes   calls   per allocation
    unpatched      6320     395         16
    patched      418176     396       1056

'percpu' field in memory.stat: 422400 (1056 bytes per process)

Memory allocation profiling now accounts the same amount of memory as
what memcg charges.

Link: https://lore.kernel.org/20261013-fix-alloc-percpu-accounting-v1-1-03e788a1e41f@kernel.org
Fixes: 60fa4a9e2323 ("mm: percpu: add codetag reference into pcpuobj_ext")
Signed-off-by: Harry Yoo (Meta) <harry@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Assisted-by: LLM # Verification
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Hao Ge <hao.ge@linux.dev>
Cc: <stable@vger.kernel.org>
---

 mm/percpu.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/percpu.c~mm-percpu-account-full-object-size-for-percpu-memory-allocations
+++ a/mm/percpu.c
@@ -1696,14 +1696,15 @@ static void pcpu_alloc_tag_alloc_hook(st
 {
 	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
 		alloc_tag_add(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag,
-			      current->alloc_tag, size);
+			      current->alloc_tag, pcpu_obj_full_size(size));
 	}
 }
 
 static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
 {
 	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts))
-		alloc_tag_sub(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag, size);
+		alloc_tag_sub(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag,
+			      pcpu_obj_full_size(size));
 }
 #else
 static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
_

Patches currently in -mm which might be from harry@kernel.org are