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 08FE7CD4F5E for ; Wed, 20 May 2026 05:31:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6A6D26B0099; Wed, 20 May 2026 01:31:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 62FA16B009B; Wed, 20 May 2026 01:31:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4D0C86B009D; Wed, 20 May 2026 01:31:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 3A7366B0099 for ; Wed, 20 May 2026 01:31:53 -0400 (EDT) Received: from smtpin30.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id E4A7E160370 for ; Wed, 20 May 2026 05:31:52 +0000 (UTC) X-FDA: 84786676464.30.8409C5B Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) by imf11.hostedemail.com (Postfix) with ESMTP id 4D70340009 for ; Wed, 20 May 2026 05:31:51 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=MjfF36VE; spf=pass (imf11.hostedemail.com: domain of shakeel.butt@linux.dev designates 91.218.175.181 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=1779255111; 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=7lMrdf7YGJu8aP4LNTUgpxJU2AI9pB1PVPoOsH0nIso=; b=7JlKiErTtViGnz9i2vkPfY3xToLfQuvx8UPdiyvWQwyGgklf4pSN40U/Bph27c+YjeOM6c xIeYgzpY/+hJWADxOkvEdcI+cbip4xeLJ7h7Bod42/sgb8cXv4fKnxS1lrztLIshwf2iBV Kpg8clzDuUKKG3RTdhJH6s0C2E7KHYY= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=MjfF36VE; spf=pass (imf11.hostedemail.com: domain of shakeel.butt@linux.dev designates 91.218.175.181 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=1779255111; a=rsa-sha256; cv=none; b=Pu28Np9q9RKjbc4FMghVmN2NjOkS3i72rg0eYQNgV59C6RAzDP+W3RVY9bTBWRkl67iGrH dODNaWFFkgYaZuaoGcRbUnVGksdNVLXeD4rdGnbmAwrylrxhxYnUjC+aXqnEhkAs89G9ff NsYQKDghBlXPkOsBZYUOZX5hgmIkWXE= 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=1779255109; 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=7lMrdf7YGJu8aP4LNTUgpxJU2AI9pB1PVPoOsH0nIso=; b=MjfF36VE6N0qJIroEBs3c8RWjCvifrIFRf2W+FK3y8LIJRXWDxnQC/v/jUJFBuKam/L0zx bzI80G/MdOX7cufTWl3IuwEU71x0Cw4SCh6A6yXRuXXfrGSpy5QNgEMwDVFhQ06NK4oPx+ hSoRJGXnisy5W5ZAcSXHPP2vrm3quXg= 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 2/4] memcg: uint16_t for nr_bytes in obj_stock_pcp Date: Tue, 19 May 2026 22:31:20 -0700 Message-ID: <20260520053123.2709959-3-shakeel.butt@linux.dev> In-Reply-To: <20260520053123.2709959-1-shakeel.butt@linux.dev> References: <20260520053123.2709959-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4D70340009 X-Rspam-User: X-Stat-Signature: xe6coju4ryjatwyzeu65jyf98ejo4w9p X-HE-Tag: 1779255111-312456 X-HE-Meta: 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 akaU9WLz x1tghLVvxPZnUUJUbe/Y29on7wk/+tgNFs86Pc3ucboKKZcrQafHBI73TLlapG9bl6fiGcJTjBj4xJNZV+EW0b56PLZKomAUOvLuFDcw4oB1jYUVU3pNwKMgKLAnVXqYf/L89BJWbSeqmz0BZwD7MJ4Wfcsb61FrpTgLVLaXMa3PTkxw9OY/qINE2BRb5ZC18O0403Lxg4TTHZSdezR7WnE+rOCA0WeYvqcDE2Hl0iWNh+sIH0xWlYsa4F236n8ANKukP0IalmJRIcu25+J600L1/3T/QuEesn2vT3OoKyLRDZQD+2da6QvHolxx9WHEXm7IZns6w4Q8Yeh4Mvihp3ziI6KxwBva6yejZZZzSecCdJL+646d5ZY7dyg== 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. Signed-off-by: Shakeel Butt Tested-by: kernel test robot --- mm/memcontrol.c | 33 +++++++++++++++++++++++++++------ 1 file changed, 27 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d7c162946719..b3d63d9f267c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2019,7 +2019,7 @@ static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = { struct obj_stock_pcp { local_trylock_t lock; - unsigned int nr_bytes; + uint16_t nr_bytes; struct obj_cgroup *cached_objcg; int16_t node_id; int nr_slab_reclaimable_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