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UPSTREAM: mm/memcg: use kmem_cache when alloc memcg

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When tracing mem_cgroup_alloc() with kmalloc ftrace, we observe:

kmalloc: call_site=mem_cgroup_css_alloc+0xd8/0x5b4 ptr=000000003e4c3799
    bytes_req=2312 bytes_alloc=4096 gfp_flags=GFP_KERNEL|__GFP_ZERO node=-1
    accounted=false

The output indicates that while allocating mem_cgroup struct (2312 bytes),
the slab allocator actually provides 4096-byte chunks. This occurs because:

1. The slab allocator predefines bucket sizes from 64B to 8096B
2. The mem_cgroup allocation size (2312B) falls between the 2KB and 4KB
   slabs
3. The allocator rounds up to the nearest larger slab (4KB), resulting in
   ~1KB wasted memory per allocation

This patch introduces a dedicated kmem_cache for mem_cgroup structs,
achieving precise memory allocation. Post-patch ftrace verification shows:

kmem_cache_alloc: call_site=mem_cgroup_css_alloc+0xbc/0x5d4
    ptr=00000000695c1806 bytes_req=2312 bytes_alloc=2368
    gfp_flags=GFP_KERNEL|__GFP_ZERO node=-1 accounted=false

Each memcg alloc offer 2368bytes(include hw cacheline align), compare to
4096, avoid waste.

Link: https://lkml.kernel.org/r/20250425031935.76411-3-link@vivo.com
Signed-off-by: Huan Yang <link@vivo.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Francesco Valla <francesco@valla.it>
Cc: guoweikang <guoweikang.kernel@gmail.com>
Cc: Huang Shijie <shijie@os.amperecomputing.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Raul E Rangel <rrangel@chromium.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 97e4fc4b35dc1b98f28671fda35bd37d4f401bca)
Change-Id: Ib5c73e7af6eaf2b3066088566690cd0c6f4c796c
Bug: 417296244
Signed-off-by: T.J. Mercier <tjmercier@google.com>
This commit is contained in:
Huan Yang
2025-04-25 11:19:24 +08:00
committed by Treehugger Robot
parent b6bde4b648
commit 78e6a3d422
1 changed files with 8 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
mm/memcontrol.c
View File

@@ -95,6 +95,8 @@ static bool cgroup_memory_nokmem __ro_after_init;
/* BPF memory accounting disabled? */ /* BPF memory accounting disabled? */
static bool cgroup_memory_nobpf __ro_after_init; static bool cgroup_memory_nobpf __ro_after_init;
static struct kmem_cache *memcg_cachep;
#ifdef CONFIG_CGROUP_WRITEBACK #ifdef CONFIG_CGROUP_WRITEBACK
static DECLARE_WAIT_QUEUE_HEAD(memcg_cgwb_frn_waitq); static DECLARE_WAIT_QUEUE_HEAD(memcg_cgwb_frn_waitq);
#endif #endif
@@ -5442,7 +5444,7 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
int __maybe_unused i; int __maybe_unused i;
long error = -ENOMEM; long error = -ENOMEM;
memcg = kzalloc(struct_size(memcg, nodeinfo, nr_node_ids), GFP_KERNEL); memcg = kmem_cache_zalloc(memcg_cachep, GFP_KERNEL);
if (!memcg) if (!memcg)
return ERR_PTR(error); return ERR_PTR(error);
@@ -7592,6 +7594,7 @@ __setup("cgroup.memory=", cgroup_memory);
*/ */
int __init mem_cgroup_init(void) int __init mem_cgroup_init(void)
{ {
unsigned int memcg_size;
int cpu, node; int cpu, node;
/* /*
@@ -7609,6 +7612,10 @@ int __init mem_cgroup_init(void)
INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work, INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work,
drain_local_stock); drain_local_stock);
memcg_size = struct_size_t(struct mem_cgroup, nodeinfo, nr_node_ids);
memcg_cachep = kmem_cache_create("mem_cgroup", memcg_size, 0,
SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL);
for_each_node(node) { for_each_node(node) {
struct mem_cgroup_tree_per_node *rtpn; struct mem_cgroup_tree_per_node *rtpn;