From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (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 1D2E123E33D for ; Fri, 22 May 2026 01:20:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779412816; cv=none; b=ieOB3sD8ppu5GGnrQ9YfNHcz+cGWe241keSPCjc/hNV6+EnBp2+wuqdJLeisyFAneWIXsyXXPsW2DnbhetSyqUXFWqr8iDDmQLbMfqsIgXtHq+1EigWWTNoo68i7c0Fyb+A29PmVZukt0Z0oMJVLFAaAE8yrWVeTiMTEqc/08bM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779412816; c=relaxed/simple; bh=vJDjCztTbemGieM7E9AKDabvaixnTahDNI3PCkVOjzI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=M5j3IgRNjqjyDuCrGo2SLsHPSEkLGl+4JdhqZvxvjXsiqrYGSTsj3G4nFUt1zxkJQQT86Uhwgv3C+EDB8bPilhDcpshMTM/trM5ncT72497P269VYfKAQvjiHVIMgp2UrxBvU7eIJSwSr/Eyl7KKabRNBxD9RbM+d01oE23kN2g= 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=jy/r4gRI; arc=none smtp.client-ip=91.218.175.184 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="jy/r4gRI" 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=1779412813; 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=vHNkZOw2UW3I07VSJDEzsPCBLxzvWAd9K3Bgudx7KQM=; b=jy/r4gRIe+INC0fMlfJlaVAV5x+Nb+kKW1ZjbpReCKKEkZqCimx5YRDWT3Q3+hCVkcV9UX 2YgRNKrwM6EBzzzk6gUti1L+SEw9QMo2ynp9MTl9SL4EgNljClhgVgTeceWaHS2AmnOZWe xndOWTYnRO2WY7oCNwoD4m2/fxcPkao= 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 v2 3/4] memcg: int16_t for cached slab stats Date: Thu, 21 May 2026 18:19:07 -0700 Message-ID: <20260522011908.1669332-4-shakeel.butt@linux.dev> In-Reply-To: <20260522011908.1669332-1-shakeel.butt@linux.dev> References: <20260522011908.1669332-1-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. Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") Tested-by: kernel test robot Signed-off-by: Shakeel Butt Reviewed-by: Harry Yoo (Oracle) --- Changes since v2: - Collected tags mm/memcontrol.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e4f00a8159d5..78c02451312b 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2022,8 +2022,8 @@ struct obj_stock_pcp { struct obj_cgroup *cached_objcg; uint16_t nr_bytes; 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