From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (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 0ADCE3B27CE for ; Tue, 26 May 2026 03:40:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779766825; cv=none; b=idu9MEAkSmrXf1lM9lgR5BDB3xsRwapA7jk0LxjKqkopa4cAL5J6wc/4bLhNTNQiIL3BMkwoDc3bJR8xpiZs5p9+Hr2SrQ5bHhTaU6BBoAxIDNtpnwG3MvILa/18P7ANwtAw05x4x54cMpEpWNMgVGWrjNhEbvKRuLYwS6A8ZnM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779766825; c=relaxed/simple; bh=wvOzrHJXCXfu+AtG3FTqF+X0QrpIulwbkMEfYzCnyUA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jxOHD2f3vWJF60BIfynlBpsmx4BjRpltAyHzOxjDqG0zrQ+MIRSvXuDoNmJpMfw3ftsk7EXggq1BztOfXfrZF/7tMwGOtoS2rFQtaiXB3gwX4lUMfNZsSbbJosGkpcc2ryfaNneW4RA+JCMOcy57IC50Vu5/j14hZptQDfSQDo8= 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=Je6Ijy+W; arc=none smtp.client-ip=91.218.175.181 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="Je6Ijy+W" 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=1779766822; 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=JUqtonBf8W/F4/BUz1cM/qYSJHRoI6UWWhfXJV6hdNs=; b=Je6Ijy+WC/N5AGJ1y2KE5X+taxE9xddABSxY7PU8tcJ6CSnJ5gycwyj84UAjwTD1/8UgNc h153RH/3//HSjvFmIx8ymq5CESp5HLezaBmIjlyPKED9ItKRV5b0TkNdIWACGQH75pHRbL CpGWgrr1uMPmRVKYOjzVu0HlpPepyn4= From: Shakeel Butt To: Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Qi Zheng , Alexandre Ghiti , Joshua Hahn , Harry Yoo , David Laight , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot Subject: [PATCH v3 3/4] memcg: int16_t for cached slab stats Date: Mon, 25 May 2026 20:39:30 -0700 Message-ID: <20260526033931.1760588-4-shakeel.butt@linux.dev> In-Reply-To: <20260526033931.1760588-1-shakeel.butt@linux.dev> References: <20260526033931.1760588-1-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 Reviewed-by: Harry Yoo (Oracle) Acked-by: Qi Zheng Acked-by: Muchun Song Signed-off-by: Shakeel Butt --- Changes since v2: - Simplify code based on David Laight's suggestion. - Collected tags Changes since v1: - Collected tags mm/memcontrol.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index be82e52c7999..fbe0e9915daa 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2035,8 +2035,8 @@ struct obj_stock_pcp { struct obj_cgroup *cached_objcg; obj_stock_bytes_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; @@ -3173,7 +3173,7 @@ 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 @@ -3210,21 +3210,20 @@ 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; + /* - * Even for large object >= PAGE_SIZE, the vmstat data will still be - * cached locally at least once before pushing it out. + * Fold @nr into the cached value and decide whether to keep it cached + * or flush it directly. Cache the combined value when it fits in the + * int16_t storage and either the cache was empty (so even a value + * above PAGE_SIZE gets a chance to be canceled by a paired delta) or + * the combined value is within the PAGE_SIZE flush threshold. */ - if (!*bytes) { + nr += *bytes; + if (abs(nr) <= S16_MAX && (!*bytes || abs(nr) <= PAGE_SIZE)) { *bytes = nr; nr = 0; } else { - *bytes += nr; - if (abs(*bytes) > PAGE_SIZE) { - nr = *bytes; - *bytes = 0; - } else { - nr = 0; - } + *bytes = 0; } direct: if (nr) -- 2.53.0-Meta