From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (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 0AF08306B1B for ; Wed, 20 May 2026 05:32:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779255127; cv=none; b=lqNxcctWfmDIoyXrQajVKNiEo0WjseBxdAFRNSac4nFq+OeMT+86W0nkkBoQUlWo7O5fQzqPXjeqUlfYcnNBfKFw7n2V92F6vYItHSJyrv2SmCAWPbiTD4PPB831QMzdMli3NvLVLttFYLeSrI+OsFGV2y6/cXzF+x8Kvywqi14= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779255127; c=relaxed/simple; bh=SzehFdc2LM/qe24HkIFFk6y9UM5HSB4TRz02KugGNu0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=etSewtObNSjA8Eh/8+/MR6YnXFUneRyq1kLALMXMT7Un1ni34j7rET241tcC08sjYgOu9UauJxFQkkfaILrKtOoZr6l09hx9nbwLYUBEawXLoLOFKqSG4ABRTncYngJlN++LCFGKkj6AWPAFe1ice+2qw9QMcFGlMavsd2B3wuo= 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=nh0efrQN; arc=none smtp.client-ip=95.215.58.181 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="nh0efrQN" 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=1779255123; 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=vmA/uDHx5nJVlFD8/rulPbhnYG25SCWOMR7+eU0w1XU=; b=nh0efrQN6xF7hr28/JCnR3ccyOfMRqcb/ECQDM+qqDdSWCyLv9oq21aX54yJBDmmHEk7nr Dzdts2JOIWvCWjuQlOfTkR4i5zYbYE02WhohsRdHxr+tjOxpv1wIBM18+NHw9Fhs+Gx7aM +HiHuQlXDuEpvY69ImnWCS3MR3rgrF8= 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 3/4] memcg: int16_t for cached slab stats Date: Tue, 19 May 2026 22:31:21 -0700 Message-ID: <20260520053123.2709959-4-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 Currently struct obj_stock_pcp stores cached slab stats in 'int' which is 4 bytes per counter on 64-bit machines. Switch them to int16_t to shrink the cached metadata. The existing PAGE_SIZE flush in __account_obj_stock() bounds *bytes at PAGE_SIZE on 4KiB and 16KiB page archs, well within int16_t. On 64KiB pages PAGE_SIZE is well above S16_MAX so that flush never fires, and a sufficiently long run of accumulations would overflow the cache. Add an explicit S16_MAX guard before each add: when the next add would push abs(*bytes) past S16_MAX, fold the cached value into @nr and flush directly via mod_objcg_mlstate() before the accumulation. Signed-off-by: Shakeel Butt Tested-by: kernel test robot --- mm/memcontrol.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b3d63d9f267c..1ed27fd06850 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2022,8 +2022,8 @@ struct obj_stock_pcp { uint16_t nr_bytes; struct obj_cgroup *cached_objcg; int16_t node_id; - int nr_slab_reclaimable_b; - int nr_slab_unreclaimable_b; + int16_t nr_slab_reclaimable_b; + int16_t nr_slab_unreclaimable_b; struct work_struct work; unsigned long flags; @@ -3158,7 +3158,7 @@ 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) { - int *bytes; + int16_t *bytes; /* * Though at the moment MAX_NUMNODES <= 1024 in all archs but let's make @@ -3195,6 +3195,16 @@ static void __account_obj_stock(struct obj_cgroup *objcg, bytes = (idx == NR_SLAB_RECLAIMABLE_B) ? &stock->nr_slab_reclaimable_b : &stock->nr_slab_unreclaimable_b; + /* + * To avoid overflow or underflow, flush directly if accumulating @nr + * would push the cached value past S16_MAX. + */ + if (abs(nr + *bytes) >= S16_MAX) { + nr += *bytes; + *bytes = 0; + goto direct; + } + /* * Even for large object >= PAGE_SIZE, the vmstat data will still be * cached locally at least once before pushing it out. -- 2.53.0-Meta