From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-183.mta1.migadu.com (out-183.mta1.migadu.com [95.215.58.183]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 89E2A306B1B for ; Wed, 20 May 2026 05:32:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779255138; cv=none; b=e+z6wRypJbPshWI9f9Rv7MezWu47V8CvtdzhS4o7R87srUHaBM3OMcAswh+QaIq5T3nIcAOOyXDrKylAu8FrxQ4VfPeg671Ry7WjnIf3EFBW4CEwIpZB4tAfotBw5ZLA0rmha7UkTnG/CKO0gEqBk/8fkvRuwvoYSPX7Q7vhKPM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779255138; c=relaxed/simple; bh=r1OKmPJykDl3nsgWMXXU9YSyK+/oVa4WOsla/TLp/Dc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=t6CCb5jpu44b/SIstlSElP/VTOD+k3aRBJZfZXnk3MgpGORIVwVxR/tQaFFIYIF7U7kEP5ardlOMa9tAUbVAK6JMctzINEmCihcciuThCR4PcbT09FcKGVKyuZ1H9OvdsPE4oMI/NQ/KX6+5f9vb7CQF57dKrQj2dFPzKAb7x6s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=aKP1eQ2O; arc=none smtp.client-ip=95.215.58.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="aKP1eQ2O" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779255134; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WYHpRVqTIOTPs8poaWY6JWzoP4/vBp/W0Ib884JadBM=; b=aKP1eQ2OWIiH+OkE2FsHyXPXO2I9NnQh9i6MNR0MBo9a3tA6SU413D11muMhrpD+zRoW1h ceLNN5KZkOUGqUSTUuHTVm8U5FlhPwCplfeyVwu+Zq/PCjg0YnZiA99esR4Ygx9eRtr+DG +1CFOdllAn4deiMztZV53eSWPUxJWs0= From: Shakeel Butt To: Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Qi Zheng , Alexandre Ghiti , Joshua Hahn , Harry Yoo , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot Subject: [PATCH 4/4] memcg: multi objcg charge support Date: Tue, 19 May 2026 22:31:22 -0700 Message-ID: <20260520053123.2709959-5-shakeel.butt@linux.dev> In-Reply-To: <20260520053123.2709959-1-shakeel.butt@linux.dev> References: <20260520053123.2709959-1-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Commit 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") split a memcg's single obj_cgroup into one per NUMA node so that reparenting LRU folios can take per-node lru locks. As a side effect, the per-CPU obj_stock_pcp -- which caches exactly one cached_objcg -- thrashes on workloads where threads of the same memcg run on different NUMA nodes. The kernel test robot reported a 67.7% regression on stress-ng.switch.ops_per_sec from this pattern. Mirror the multi-slot pattern already used by memcg_stock_pcp: turn nr_bytes and cached_objcg into NR_OBJ_STOCK-element arrays, scan all slots on consume/refill/account, prefer empty slots when inserting, and evict a random slot only when full. With multiple slots a CPU can hold the per-node objcg variants of one memcg plus a few siblings without ever forcing a drain. A single int8_t index records which slot the cached slab stats belong to; the stats are flushed on slot or pgdat change. With NR_OBJ_STOCK = 5 the layout (verified with pahole) is: offset 0 : lock(1) + index(1) + node_id(2) + slab stats(4) = 8B offset 8 : nr_bytes[5] = 10B offset 18 : padding = 6B offset 24 : cached[5] = 40B offset 64 : (line 2) work_struct + flags (cold) so consume_obj_stock, refill_obj_stock and the slab account path each touch exactly one 64-byte cache line on non-debug 64-bit builds. Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202605121641.b6a60cb0-lkp@intel.com Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") Signed-off-by: Shakeel Butt Tested-by: kernel test robot --- mm/memcontrol.c | 185 ++++++++++++++++++++++++++++++++++-------------- 1 file changed, 133 insertions(+), 52 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 1ed27fd06850..52104cbb8e7c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -150,14 +150,14 @@ static void obj_cgroup_release(struct percpu_ref *ref) * However, it can be PAGE_SIZE or (x * PAGE_SIZE). * * The following sequence can lead to it: - * 1) CPU0: objcg == stock->cached_objcg + * 1) CPU0: objcg cached in one of stock->cached[i] * 2) CPU1: we do a small allocation (e.g. 92 bytes), * PAGE_SIZE bytes are charged * 3) CPU1: a process from another memcg is allocating something, * the stock if flushed, * objcg->nr_charged_bytes = PAGE_SIZE - 92 * 5) CPU0: we do release this object, - * 92 bytes are added to stock->nr_bytes + * 92 bytes are added to stock->nr_bytes[i] * 6) CPU0: stock is flushed, * 92 bytes are added to objcg->nr_charged_bytes * @@ -2017,13 +2017,25 @@ static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = { .lock = INIT_LOCAL_TRYLOCK(lock), }; +/* + * NR_OBJ_STOCK is sized so the entire hot path of obj_stock_pcp + * (lock, accounting metadata, nr_bytes[] and cached[]) fits within a + * single 64-byte cache line on non-debug 64-bit builds. With 5 slots: + * lock(1) + index(1) + node_id(2) + slab stats(4) + nr_bytes(10) + * + pad(6) + cached(40) == 64 bytes. + * A CPU can thus consume/refill/account against five different objcgs + * (typically per-node variants of the same memcg) while incurring at + * most one cache miss on the stock. + */ +#define NR_OBJ_STOCK 5 struct obj_stock_pcp { local_trylock_t lock; - uint16_t nr_bytes; - struct obj_cgroup *cached_objcg; + int8_t index; int16_t node_id; int16_t nr_slab_reclaimable_b; int16_t nr_slab_unreclaimable_b; + uint16_t nr_bytes[NR_OBJ_STOCK]; + struct obj_cgroup *cached[NR_OBJ_STOCK]; struct work_struct work; unsigned long flags; @@ -2031,11 +2043,13 @@ struct obj_stock_pcp { static DEFINE_PER_CPU_ALIGNED(struct obj_stock_pcp, obj_stock) = { .lock = INIT_LOCAL_TRYLOCK(lock), + .index = -1, .node_id = NUMA_NO_NODE, }; static DEFINE_MUTEX(percpu_charge_mutex); +static void drain_obj_stock_slot(struct obj_stock_pcp *stock, int i); static void drain_obj_stock(struct obj_stock_pcp *stock); static bool obj_stock_flush_required(struct obj_stock_pcp *stock, struct mem_cgroup *root_memcg); @@ -3153,12 +3167,13 @@ static void unlock_stock(struct obj_stock_pcp *stock) local_unlock(&obj_stock.lock); } -/* Call after __refill_obj_stock() to ensure stock->cached_objg == objcg */ +/* Call after __refill_obj_stock() so a slot for objcg exists in the stock */ static void __account_obj_stock(struct obj_cgroup *objcg, struct obj_stock_pcp *stock, int nr, struct pglist_data *pgdat, enum node_stat_item idx) { int16_t *bytes; + int i; /* * Though at the moment MAX_NUMNODES <= 1024 in all archs but let's make @@ -3167,29 +3182,39 @@ static void __account_obj_stock(struct obj_cgroup *objcg, */ BUILD_BUG_ON(MAX_NUMNODES >= S16_MAX); - if (!stock || READ_ONCE(stock->cached_objcg) != objcg) + if (!stock) + goto direct; + + for (i = 0; i < NR_OBJ_STOCK; ++i) { + if (READ_ONCE(stock->cached[i]) == objcg) + break; + } + if (i == NR_OBJ_STOCK) goto direct; /* * Save vmstat data in stock and skip vmstat array update unless - * accumulating over a page of vmstat data or when pgdat changes. + * accumulating over a page of vmstat data or when the objcg slot or + * pgdat the stats belong to changes. */ - if (stock->node_id == NUMA_NO_NODE) { + if (stock->index < 0) { + stock->index = i; stock->node_id = pgdat->node_id; - } else if (stock->node_id != pgdat->node_id) { - /* Flush the existing cached vmstat data */ + } else if (stock->index != i || stock->node_id != pgdat->node_id) { + struct obj_cgroup *old = READ_ONCE(stock->cached[stock->index]); struct pglist_data *oldpg = NODE_DATA(stock->node_id); if (stock->nr_slab_reclaimable_b) { - mod_objcg_mlstate(objcg, oldpg, NR_SLAB_RECLAIMABLE_B, + mod_objcg_mlstate(old, oldpg, NR_SLAB_RECLAIMABLE_B, stock->nr_slab_reclaimable_b); stock->nr_slab_reclaimable_b = 0; } if (stock->nr_slab_unreclaimable_b) { - mod_objcg_mlstate(objcg, oldpg, NR_SLAB_UNRECLAIMABLE_B, + mod_objcg_mlstate(old, oldpg, NR_SLAB_UNRECLAIMABLE_B, stock->nr_slab_unreclaimable_b); stock->nr_slab_unreclaimable_b = 0; } + stock->index = i; stock->node_id = pgdat->node_id; } @@ -3230,10 +3255,16 @@ static bool __consume_obj_stock(struct obj_cgroup *objcg, struct obj_stock_pcp *stock, unsigned int nr_bytes) { - if (objcg == READ_ONCE(stock->cached_objcg) && - stock->nr_bytes >= nr_bytes) { - stock->nr_bytes -= nr_bytes; - return true; + int i; + + for (i = 0; i < NR_OBJ_STOCK; ++i) { + if (READ_ONCE(stock->cached[i]) != objcg) + continue; + if (stock->nr_bytes[i] >= nr_bytes) { + stock->nr_bytes[i] -= nr_bytes; + return true; + } + return false; } return false; @@ -3254,16 +3285,42 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) return ret; } -static void drain_obj_stock(struct obj_stock_pcp *stock) +/* Flush the cached slab stats (if any) back to their owning objcg/pgdat. */ +static void drain_obj_stock_stats(struct obj_stock_pcp *stock) { - struct obj_cgroup *old = READ_ONCE(stock->cached_objcg); + struct obj_cgroup *old; + struct pglist_data *oldpg; + + if (stock->index < 0) + return; + + old = READ_ONCE(stock->cached[stock->index]); + oldpg = NODE_DATA(stock->node_id); + + if (stock->nr_slab_reclaimable_b) { + mod_objcg_mlstate(old, oldpg, NR_SLAB_RECLAIMABLE_B, + stock->nr_slab_reclaimable_b); + stock->nr_slab_reclaimable_b = 0; + } + if (stock->nr_slab_unreclaimable_b) { + mod_objcg_mlstate(old, oldpg, NR_SLAB_UNRECLAIMABLE_B, + stock->nr_slab_unreclaimable_b); + stock->nr_slab_unreclaimable_b = 0; + } + stock->index = -1; + stock->node_id = NUMA_NO_NODE; +} + +static void drain_obj_stock_slot(struct obj_stock_pcp *stock, int i) +{ + struct obj_cgroup *old = READ_ONCE(stock->cached[i]); if (!old) return; - if (stock->nr_bytes) { - unsigned int nr_pages = stock->nr_bytes >> PAGE_SHIFT; - unsigned int nr_bytes = stock->nr_bytes & (PAGE_SIZE - 1); + if (stock->nr_bytes[i]) { + unsigned int nr_pages = stock->nr_bytes[i] >> PAGE_SHIFT; + unsigned int nr_bytes = stock->nr_bytes[i] & (PAGE_SIZE - 1); if (nr_pages) { struct mem_cgroup *memcg; @@ -3289,46 +3346,43 @@ static void drain_obj_stock(struct obj_stock_pcp *stock) * so it might be changed in the future. */ atomic_add(nr_bytes, &old->nr_charged_bytes); - stock->nr_bytes = 0; + stock->nr_bytes[i] = 0; } - /* - * Flush the vmstat data in current stock - */ - if (stock->nr_slab_reclaimable_b || stock->nr_slab_unreclaimable_b) { - struct pglist_data *oldpg = NODE_DATA(stock->node_id); - - if (stock->nr_slab_reclaimable_b) { - mod_objcg_mlstate(old, oldpg, - NR_SLAB_RECLAIMABLE_B, - stock->nr_slab_reclaimable_b); - stock->nr_slab_reclaimable_b = 0; - } - if (stock->nr_slab_unreclaimable_b) { - mod_objcg_mlstate(old, oldpg, - NR_SLAB_UNRECLAIMABLE_B, - stock->nr_slab_unreclaimable_b); - stock->nr_slab_unreclaimable_b = 0; - } - stock->node_id = NUMA_NO_NODE; - } + /* Flush vmstat data when its owning slot is being drained. */ + if (stock->index == i) + drain_obj_stock_stats(stock); - WRITE_ONCE(stock->cached_objcg, NULL); + WRITE_ONCE(stock->cached[i], NULL); obj_cgroup_put(old); } +static void drain_obj_stock(struct obj_stock_pcp *stock) +{ + int i; + + for (i = 0; i < NR_OBJ_STOCK; ++i) + drain_obj_stock_slot(stock, i); +} + static bool obj_stock_flush_required(struct obj_stock_pcp *stock, struct mem_cgroup *root_memcg) { - struct obj_cgroup *objcg = READ_ONCE(stock->cached_objcg); + struct obj_cgroup *objcg; struct mem_cgroup *memcg; bool flush = false; + int i; rcu_read_lock(); - if (objcg) { + for (i = 0; i < NR_OBJ_STOCK; ++i) { + objcg = READ_ONCE(stock->cached[i]); + if (!objcg) + continue; memcg = obj_cgroup_memcg(objcg); - if (memcg && mem_cgroup_is_descendant(memcg, root_memcg)) + if (memcg && mem_cgroup_is_descendant(memcg, root_memcg)) { flush = true; + break; + } } rcu_read_unlock(); @@ -3342,6 +3396,7 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, { unsigned int nr_pages = 0; unsigned int stock_nr_bytes; + int i, slot = -1, empty_slot = -1; if (!stock) { nr_pages = nr_bytes >> PAGE_SHIFT; @@ -3350,19 +3405,45 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, goto out; } - stock_nr_bytes = stock->nr_bytes; - if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */ - drain_obj_stock(stock); + for (i = 0; i < NR_OBJ_STOCK; ++i) { + struct obj_cgroup *cached = READ_ONCE(stock->cached[i]); + + if (!cached) { + if (empty_slot == -1) + empty_slot = i; + continue; + } + if (cached == objcg) { + slot = i; + break; + } + } + + if (slot == -1) { + slot = empty_slot; + if (slot == -1) { + slot = get_random_u32_below(NR_OBJ_STOCK); + drain_obj_stock_slot(stock, slot); + } obj_cgroup_get(objcg); + /* + * Keep the xchg result in the unsigned int local; storing + * it directly into stock->nr_bytes[slot] (uint16_t) would + * silently truncate values >= U16_MAX and bypass the flush + * guard below, leaking page-counter charges. + */ stock_nr_bytes = atomic_read(&objcg->nr_charged_bytes) ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; - WRITE_ONCE(stock->cached_objcg, objcg); + WRITE_ONCE(stock->cached[slot], objcg); allow_uncharge = true; /* Allow uncharge when objcg changes */ + } else { + stock_nr_bytes = stock->nr_bytes[slot]; } + stock_nr_bytes += nr_bytes; - /* Since stock->nr_bytes is uint16_t, don't refill >= U16_MAX */ + /* nr_bytes[] is uint16_t; flush if we would refill >= U16_MAX. */ if ((allow_uncharge && (stock_nr_bytes > PAGE_SIZE)) || stock_nr_bytes >= U16_MAX) { nr_pages = stock_nr_bytes >> PAGE_SHIFT; @@ -3384,7 +3465,7 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, stock_nr_bytes = kept; } } - stock->nr_bytes = stock_nr_bytes; + stock->nr_bytes[slot] = stock_nr_bytes; out: if (nr_pages) -- 2.53.0-Meta