[PATCH v2] mm/percpu: clean up callers of pcpu_obj_full_size()

[PATCH v2] mm/percpu: clean up callers of pcpu_obj_full_size()

[Joshua Hahn]

The size of a pcpu allocation can be interpreted in two ways:
1. The size of the allocation attributable to a single CPU.
2. The total size of the allocation across all CPUs, including the
   allocation overhead (for obj_cgroup membership).

In most accounting paths for percpu memory, we need the second
definition (full size). Make this more obvious by coalescing the
callers of pcpu_obj_full_size() and renaming the parameter to full_size
to distinguish between the two definitions above.

No functional changes intended.

Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
---
v1 --> v2
- Renamed the function parameter from size to full_size where
  appropriate now that pcpu_obj_full_size(size) is passed in, as
  suggested by Harry Yoo.
- Wordsmithing.

 mm/percpu.c | 63 +++++++++++++++++++++++++++++------------------------
 1 file changed, 34 insertions(+), 29 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index d7883507dc151..b22a16980f646 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1611,7 +1611,7 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
 }
 
 #ifdef CONFIG_MEMCG
-static bool pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,
+static bool pcpu_memcg_pre_alloc_hook(size_t full_size, gfp_t gfp,
 				      struct obj_cgroup **objcgp)
 {
 	struct obj_cgroup *objcg;
@@ -1623,7 +1623,7 @@ static bool pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,
 	if (!objcg || obj_cgroup_is_root(objcg))
 		return true;
 
-	if (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size)))
+	if (obj_cgroup_charge(objcg, gfp, full_size))
 		return false;
 
 	*objcgp = objcg;
@@ -1632,7 +1632,7 @@ static bool pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,
 
 static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
 				       struct pcpu_chunk *chunk, int off,
-				       size_t size)
+				       size_t full_size)
 {
 	if (!objcg)
 		return;
@@ -1643,14 +1643,15 @@ static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
 
 		rcu_read_lock();
 		mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
-				pcpu_obj_full_size(size));
+				full_size);
 		rcu_read_unlock();
 	} else {
-		obj_cgroup_uncharge(objcg, pcpu_obj_full_size(size));
+		obj_cgroup_uncharge(objcg, full_size);
 	}
 }
 
-static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
+static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off,
+				 size_t full_size)
 {
 	struct obj_cgroup *objcg;
 
@@ -1662,57 +1663,59 @@ static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
 		return;
 	chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].cgroup = NULL;
 
-	obj_cgroup_uncharge(objcg, pcpu_obj_full_size(size));
+	obj_cgroup_uncharge(objcg, full_size);
 
 	rcu_read_lock();
-	mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
-			-pcpu_obj_full_size(size));
+	mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B, -full_size);
 	rcu_read_unlock();
 
 	obj_cgroup_put(objcg);
 }
 
 #else /* CONFIG_MEMCG */
-static bool
-pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp, struct obj_cgroup **objcgp)
+static bool pcpu_memcg_pre_alloc_hook(size_t full_size, gfp_t gfp,
+				      struct obj_cgroup **objcgp)
 {
 	return true;
 }
 
 static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
 				       struct pcpu_chunk *chunk, int off,
-				       size_t size)
+				       size_t full_size)
 {
 }
 
-static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
+static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off,
+				 size_t full_size)
 {
 }
 #endif /* CONFIG_MEMCG */
 
 #ifdef CONFIG_MEM_ALLOC_PROFILING
 static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
-				      size_t size)
+				      size_t full_size)
 {
 	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
 		alloc_tag_add(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag,
-			      current->alloc_tag, pcpu_obj_full_size(size));
+			      current->alloc_tag, full_size);
 	}
 }
 
-static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
+static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off,
+				     size_t full_size)
 {
 	if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts))
 		alloc_tag_sub(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag,
-			      pcpu_obj_full_size(size));
+			      full_size);
 }
 #else
 static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
-				      size_t size)
+				      size_t full_size)
 {
 }
 
-static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
+static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off,
+				     size_t full_size)
 {
 }
 #endif
@@ -1744,7 +1747,7 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved,
 	int slot, off, cpu, ret;
 	unsigned long flags;
 	void __percpu *ptr;
-	size_t bits, bit_align;
+	size_t bits, bit_align, full_size;
 
 	gfp = current_gfp_context(gfp);
 	/*
@@ -1773,6 +1776,7 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved,
 	size = ALIGN(size, PCPU_MIN_ALLOC_SIZE);
 	bits = size >> PCPU_MIN_ALLOC_SHIFT;
 	bit_align = align >> PCPU_MIN_ALLOC_SHIFT;
+	full_size = pcpu_obj_full_size(size);
 
 	if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE ||
 		     !is_power_of_2(align))) {
@@ -1781,7 +1785,7 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved,
 		return NULL;
 	}
 
-	if (unlikely(!pcpu_memcg_pre_alloc_hook(size, gfp, &objcg)))
+	if (unlikely(!pcpu_memcg_pre_alloc_hook(full_size, gfp, &objcg)))
 		return NULL;
 
 	if (!is_atomic) {
@@ -1793,7 +1797,7 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved,
 		if (gfp & __GFP_NOFAIL) {
 			mutex_lock(&pcpu_alloc_mutex);
 		} else if (mutex_lock_killable(&pcpu_alloc_mutex)) {
-			pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size);
+			pcpu_memcg_post_alloc_hook(objcg, NULL, 0, full_size);
 			return NULL;
 		}
 	}
@@ -1903,12 +1907,11 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved,
 	kmemleak_alloc_percpu(ptr, size, gfp);
 
 	trace_percpu_alloc_percpu(_RET_IP_, reserved, is_atomic, size, align,
-				  chunk->base_addr, off, ptr,
-				  pcpu_obj_full_size(size), gfp);
+				  chunk->base_addr, off, ptr, full_size, gfp);
 
-	pcpu_memcg_post_alloc_hook(objcg, chunk, off, size);
+	pcpu_memcg_post_alloc_hook(objcg, chunk, off, full_size);
 
-	pcpu_alloc_tag_alloc_hook(chunk, off, size);
+	pcpu_alloc_tag_alloc_hook(chunk, off, full_size);
 
 	return ptr;
 
@@ -1938,7 +1941,7 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved,
 		mutex_unlock(&pcpu_alloc_mutex);
 	}
 
-	pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size);
+	pcpu_memcg_post_alloc_hook(objcg, NULL, 0, full_size);
 
 	return NULL;
 }
@@ -2242,6 +2245,7 @@ void free_percpu(void __percpu *ptr)
 	struct pcpu_chunk *chunk;
 	unsigned long flags;
 	int size, off;
+	size_t full_size;
 	bool need_balance = false;
 
 	if (!ptr)
@@ -2262,10 +2266,11 @@ void free_percpu(void __percpu *ptr)
 		WARN_ON_ONCE(1);
 		return;
 	}
+	full_size = pcpu_obj_full_size(size);
 
-	pcpu_alloc_tag_free_hook(chunk, off, size);
+	pcpu_alloc_tag_free_hook(chunk, off, full_size);
 
-	pcpu_memcg_free_hook(chunk, off, size);
+	pcpu_memcg_free_hook(chunk, off, full_size);
 
 	/*
 	 * If there are more than one fully free chunks, wake up grim reaper.
-- 
2.53.0-Meta

Re: [PATCH v2] mm/percpu: clean up callers of pcpu_obj_full_size()

[Harry Yoo]

On Tue, Oct 20, 2026 at 07:30:11PM -0700, Joshua Hahn wrote:
> The size of a pcpu allocation can be interpreted in two ways:
> 1. The size of the allocation attributable to a single CPU.
> 2. The total size of the allocation across all CPUs, including the
>    allocation overhead (for obj_cgroup membership).
> 
> In most accounting paths for percpu memory, we need the second
> definition (full size). Make this more obvious by coalescing the
> callers of pcpu_obj_full_size() and renaming the parameter to full_size
> to distinguish between the two definitions above.
> 
> No functional changes intended.
> 
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> ---

Looks good to me,
Reviewed-by: Harry Yoo (Meta) <harry@kernel.org>

Thanks!

-- 
Cheers,
Harry / Hyeonggon