mm: percpu: introduce pcpuobj_ext

Upcoming alloc tagging patches require a place to stash per-allocation
metadata.

We already do this when memcg is enabled, so this patch generalizes the
obj_cgroup * vector in struct pcpu_chunk by creating a pcpu_obj_ext type,
which we will be adding to in an upcoming patch - similarly to the
previous slabobj_ext patch.

Link: https://lkml.kernel.org/r/20240321163705.3067592-28-surenb@google.comSigned-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Tested-by: Kees Cook <keescook@chromium.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: linux-mm@kvack.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alex Gaynor <alex.gaynor@gmail.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Andreas Hindborg <a.hindborg@samsung.com>
Cc: Benno Lossin <benno.lossin@proton.me>
Cc: "Björn Roy Baron" <bjorn3_gh@protonmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Gary Guo <gary@garyguo.net>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/percpu-internal.h

@@ -32,6 +32,16 @@ struct pcpu_block_md {
 	int			nr_bits;	/* total bits responsible for */
 };
 
+struct pcpuobj_ext {
+#ifdef CONFIG_MEMCG_KMEM
+	struct obj_cgroup	*cgroup;
+#endif
+};
+
+#ifdef CONFIG_MEMCG_KMEM
+#define NEED_PCPUOBJ_EXT
+#endif
+
 struct pcpu_chunk {
 #ifdef CONFIG_PERCPU_STATS
 	int			nr_alloc;	/* # of allocations */
@@ -64,8 +74,8 @@ struct pcpu_chunk {
 	int			end_offset;	/* additional area required to
 						   have the region end page
 						   aligned */
-#ifdef CONFIG_MEMCG_KMEM
-	struct obj_cgroup	**obj_cgroups;	/* vector of object cgroups */
+#ifdef NEED_PCPUOBJ_EXT
+	struct pcpuobj_ext	*obj_exts;	/* vector of object cgroups */
 #endif
 
 	int			nr_pages;	/* # of pages served by this chunk */
@@ -74,6 +84,11 @@ struct pcpu_chunk {
 	unsigned long		populated[];	/* populated bitmap */
 };
 
+static inline bool need_pcpuobj_ext(void)
+{
+	return !mem_cgroup_kmem_disabled();
+}
+
 extern spinlock_t pcpu_lock;
 
 extern struct list_head *pcpu_chunk_lists;

mm/percpu.c

@@ -1392,9 +1392,9 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
 		panic("%s: Failed to allocate %zu bytes\n", __func__,
 		      alloc_size);
 
-#ifdef CONFIG_MEMCG_KMEM
+#ifdef NEED_PCPUOBJ_EXT
 	/* first chunk is free to use */
-	chunk->obj_cgroups = NULL;
+	chunk->obj_exts = NULL;
 #endif
 	pcpu_init_md_blocks(chunk);
 
@@ -1463,12 +1463,12 @@ static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t gfp)
 	if (!chunk->md_blocks)
 		goto md_blocks_fail;
 
-#ifdef CONFIG_MEMCG_KMEM
-	if (!mem_cgroup_kmem_disabled()) {
-		chunk->obj_cgroups =
+#ifdef NEED_PCPUOBJ_EXT
+	if (need_pcpuobj_ext()) {
+		chunk->obj_exts =
 			pcpu_mem_zalloc(pcpu_chunk_map_bits(chunk) *
-					sizeof(struct obj_cgroup *), gfp);
-		if (!chunk->obj_cgroups)
+					sizeof(struct pcpuobj_ext), gfp);
+		if (!chunk->obj_exts)
 			goto objcg_fail;
 	}
 #endif
@@ -1480,7 +1480,7 @@ static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t gfp)
 
 	return chunk;
 
-#ifdef CONFIG_MEMCG_KMEM
+#ifdef NEED_PCPUOBJ_EXT
 objcg_fail:
 	pcpu_mem_free(chunk->md_blocks);
 #endif
@@ -1498,8 +1498,8 @@ static void pcpu_free_chunk(struct pcpu_chunk *chunk)
 {
 	if (!chunk)
 		return;
-#ifdef CONFIG_MEMCG_KMEM
-	pcpu_mem_free(chunk->obj_cgroups);
+#ifdef NEED_PCPUOBJ_EXT
+	pcpu_mem_free(chunk->obj_exts);
 #endif
 	pcpu_mem_free(chunk->md_blocks);
 	pcpu_mem_free(chunk->bound_map);
@@ -1646,9 +1646,9 @@ static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
 	if (!objcg)
 		return;
 
-	if (likely(chunk && chunk->obj_cgroups)) {
+	if (likely(chunk && chunk->obj_exts)) {
 		obj_cgroup_get(objcg);
-		chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = objcg;
+		chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].cgroup = objcg;
 
 		rcu_read_lock();
 		mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
@@ -1663,13 +1663,13 @@ static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
 {
 	struct obj_cgroup *objcg;
 
-	if (unlikely(!chunk->obj_cgroups))
+	if (unlikely(!chunk->obj_exts))
 		return;
 
-	objcg = chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT];
+	objcg = chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].cgroup;
 	if (!objcg)
 		return;
-	chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = NULL;
+	chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].cgroup = NULL;
 
 	obj_cgroup_uncharge(objcg, pcpu_obj_full_size(size));