From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DCA3FCD5BAF for ; Fri, 22 May 2026 01:19:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 397366B009D; Thu, 21 May 2026 21:19:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 36E8E6B009E; Thu, 21 May 2026 21:19:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 284286B009F; Thu, 21 May 2026 21:19:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 1B1676B009D for ; Thu, 21 May 2026 21:19:54 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id D36BC12094B for ; Fri, 22 May 2026 01:19:53 +0000 (UTC) X-FDA: 84793299066.12.6A0E281 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) by imf26.hostedemail.com (Postfix) with ESMTP id 4935E140009 for ; Fri, 22 May 2026 01:19:52 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="LBjWDd/H"; spf=pass (imf26.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.187 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1779412792; a=rsa-sha256; cv=none; b=RbIkbcwqtxsMProYTF7b/ZBpRrNuVtzlpBAVjPMe5pr07YRt+pEyf4qijyPRU3pyqoO6U4 XGQJTRVu2yf09rbci9wD0Sd5ACqQFZ5wyMVdFhIWhoJxZ+8pSvhgDrY5V/4Y2rXYycq6Fo IIzyihCWjWuwe/TEnUcoSfZYYEUYOmc= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="LBjWDd/H"; spf=pass (imf26.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.187 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1779412792; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=j0DDjB0w4E9tMqU+JEwxbi4iz46ciqDj+g3fDXVBUs8=; b=Wkqvylh8SS5ADsgcOiSBY/zfAZ40GTx+ZJm481NeQnI2bW8QddqDJIFYFYMTNyFhnk8Jv4 J6BCHawblLYtrmQEQOZDJB9+zWHB3iu4M299BiZG+AYU9w+/Z04kkfxnc5z4rmw3SMJQyq zgLYYcNd4wDidxwMIHgMi23s8KaG6QE= 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=1779412790; 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=j0DDjB0w4E9tMqU+JEwxbi4iz46ciqDj+g3fDXVBUs8=; b=LBjWDd/HeERmF6Rf8dihT6KKDeCm9NG6KIIBMxZfB69IOMazt2pX6Wn1nfoXxIAKbwbL4z lfv2KcxH0aceH3Bm/26jxoCn9id9qEBK1UyJ2oUDuD3LLhAQx763nh7zneCEZvHkdNufhi qiEAedwMNnd+OQ4XUAgQaNtBDY9ria0= 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 2/4] memcg: uint16_t for nr_bytes in obj_stock_pcp Date: Thu, 21 May 2026 18:19:06 -0700 Message-ID: <20260522011908.1669332-3-shakeel.butt@linux.dev> In-Reply-To: <20260522011908.1669332-1-shakeel.butt@linux.dev> References: <20260522011908.1669332-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 4935E140009 X-Rspamd-Server: rspam03 X-Stat-Signature: sjtm8pdutn8hjwks5i5craqwfnmurzxt X-HE-Tag: 1779412792-343614 X-HE-Meta: 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 HnJ2Av0o 8kjqtiNmcqAkKgXMeoatMIf/c0CIyUSAPX/v0oVFyJTYmcN1UtxEkj8Td9tWmrFN6GW3sQ8UAPhQwMsuArVBWVXBLTdQX5MRwdZoizRYIIgrsM2+agDoM7AFDOh8IQHnKL/qFVilVMWiTAqYNGkc32icOZeBTSN0GftIiAH6ni4EHjDT7FpVxOBbtld7frNWtKwHdLNXgbFR+apkWL/CqrXYlma8ERXtoET9JPC7Vy0gOtDTrko/fe0A3j6zlu9Yh3BEL/NNpOLt1BbDTwZeUQ6r6h4NzIDY7DCPq5xE7teHhIftu7XawAQhnZCQJU5jtSpMns0gQww8kUKuVBzh/WNpj6GpddoqnfG8q3aItTIS6Hiw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Currently struct obj_stock_pcp stores nr_bytes in an 'unsigned int' which is 4 bytes on 64-bit machines. Switch the field to uint16_t to shrink the per-CPU cache. The kernel supports PAGE_SIZE_4KB, _8KB, _16KB, _32KB, _64KB and _256KB (see HAVE_PAGE_SIZE_* in arch/Kconfig). After the PAGE_SIZE-aligned flush in __refill_obj_stock(), the sub-page remainder fits in uint16_t up through 64KiB pages where PAGE_SIZE - 1 == U16_MAX, but on 256KiB pages PAGE_SIZE - 1 == 0x3FFFF exceeds U16_MAX. The accumulator also needs to stay within uint16_t between page-aligned flushes on 64KiB pages where PAGE_SIZE itself is U16_MAX + 1. Accumulate the new total in an 'unsigned int' local, then: 1. Flush whenever the accumulator would hit U16_MAX. Together with the existing allow_uncharge flush at PAGE_SIZE, this keeps the uint16_t safe on PAGE_SIZE <= 64KiB. 2. On configs with PAGE_SHIFT > 16 (PAGE_SIZE_256KB on hexagon and powerpc 44x), push any sub-page remainder above U16_MAX into objcg->nr_charged_bytes via atomic_add before storing back, so the store cannot silently truncate. The PAGE_SHIFT > 16 guard folds the branch out at compile time on smaller page sizes. 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 v1: - Collected tags - Rearrange fields of obj_stock_pcp (David Laight) - Fix comparison operator (Harry) mm/memcontrol.c | 33 +++++++++++++++++++++++++++------ 1 file changed, 27 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d7c162946719..e4f00a8159d5 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2019,8 +2019,8 @@ static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = { struct obj_stock_pcp { local_trylock_t lock; - unsigned int nr_bytes; struct obj_cgroup *cached_objcg; + uint16_t nr_bytes; int16_t node_id; int nr_slab_reclaimable_b; int nr_slab_unreclaimable_b; @@ -3331,6 +3331,7 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, bool allow_uncharge) { unsigned int nr_pages = 0; + unsigned int stock_nr_bytes; if (!stock) { nr_pages = nr_bytes >> PAGE_SHIFT; @@ -3339,21 +3340,41 @@ 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); obj_cgroup_get(objcg); - stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) + stock_nr_bytes = atomic_read(&objcg->nr_charged_bytes) ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; WRITE_ONCE(stock->cached_objcg, objcg); allow_uncharge = true; /* Allow uncharge when objcg changes */ } - stock->nr_bytes += nr_bytes; + stock_nr_bytes += nr_bytes; + + /* Since stock->nr_bytes is uint16_t, don't refill >= U16_MAX */ + if ((allow_uncharge && (stock_nr_bytes > PAGE_SIZE)) || + stock_nr_bytes > U16_MAX) { + nr_pages = stock_nr_bytes >> PAGE_SHIFT; + stock_nr_bytes &= (PAGE_SIZE - 1); + + /* + * On configs with PAGE_SHIFT > 16 (PAGE_SIZE_256KB on + * hexagon and powerpc 44x), the sub-page remainder can + * still exceed U16_MAX. Push the excess back to + * objcg->nr_charged_bytes so the store into uint16_t + * cannot silently truncate; folded out at compile time + * on smaller page sizes. + */ + if (PAGE_SHIFT > 16 && stock_nr_bytes > U16_MAX) { + unsigned int kept = stock_nr_bytes & U16_MAX; - if (allow_uncharge && (stock->nr_bytes > PAGE_SIZE)) { - nr_pages = stock->nr_bytes >> PAGE_SHIFT; - stock->nr_bytes &= (PAGE_SIZE - 1); + atomic_add(stock_nr_bytes - kept, + &objcg->nr_charged_bytes); + stock_nr_bytes = kept; + } } + stock->nr_bytes = stock_nr_bytes; out: if (nr_pages) -- 2.53.0-Meta