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 C2CB2CF2567 for ; Wed, 19 Nov 2025 07:43:09 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 280A96B0062; Wed, 19 Nov 2025 02:43:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 231026B00B2; Wed, 19 Nov 2025 02:43:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0F9846B00B3; Wed, 19 Nov 2025 02:43:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id EC4C66B0062 for ; Wed, 19 Nov 2025 02:43:08 -0500 (EST) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 9E5E84DE46 for ; Wed, 19 Nov 2025 07:43:08 +0000 (UTC) X-FDA: 84126565656.14.CDE2A4C Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) by imf19.hostedemail.com (Postfix) with ESMTP id B986E1A0004 for ; Wed, 19 Nov 2025 07:43:06 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=l3SMmJV7; spf=pass (imf19.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.181 as permitted sender) smtp.mailfrom=qi.zheng@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=1763538187; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=1I7cA2fVYEnU5tKmvwQ5dB4/kePKxlMyfJS/i/M6zD8=; b=DGpqfj47afNUhMXDbaldXX/UJhvuA7abOrT78tYVZRKqlF4AylbYl+zcbomTI3ns1HqjSa HbgQQpG2+qIrZ7S3FjtnQT/urb74/8SqVPTPo0oDUt2KFrSCVjewS/boHu8FpV2PzMqH7C w8+lpwUaZjblS/i1LKfZJn3wQjjpmlM= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=l3SMmJV7; spf=pass (imf19.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.181 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763538187; a=rsa-sha256; cv=none; b=4BE35+dNU6GOogs5CYjp1JnUQnu7emsHGtEPzWRn5SYGrYWKz2BIxlLamF19WSha24/7k1 axeDNKf2eAjJpghEoxuINnYG2DtJYCu0l10BB+8+CgNoJ91fO+8ReSL029nCvnlNbA/z8x r8HGDyYujR4lDdp7lrAVaZCbjFABgxk= Message-ID: <938180ff-7e24-4d73-87d5-fca4bbaa4ced@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1763538184; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1I7cA2fVYEnU5tKmvwQ5dB4/kePKxlMyfJS/i/M6zD8=; b=l3SMmJV7Df/YlzQosv4zjnQtzbyfuENKua4z6s08PbQodhAK/In9ZUM9Y4NRbSBMPVkJWa 1sExjcueECfivNB8hdidZd1kutWfWzzwrDPl+CgFixJsdFwbKXBqpujVjgPrjI/JsEU0qa gDayA0fLuY27pEbzURnI6Awwg70OeaE= Date: Wed, 19 Nov 2025 15:42:51 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v1 06/26] mm: memcontrol: return root object cgroup for root memory cgroup To: Harry Yoo Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng References: <5e9743f291e7ca7b8f052775e993090ed66cfa80.1761658310.git.zhengqi.arch@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B986E1A0004 X-Stat-Signature: aj6joqeoksqgctr8yi6oa97zxuws7xzb X-Rspam-User: X-HE-Tag: 1763538186-155682 X-HE-Meta: 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 lZu4GY76 +eaVcKyLK4kgEEMr/042sgtRhECSkAjPostk7ly9PNRJUWgQReYYNwi8ozz5WdxxLp92PQOCktcqmpTAHsr/XgmD/83rbipy+v6FyfJpMm5fdtU4HlU29ZdQ7Knk7Lk0bCSip3rhAnTL1zHZRA7k8Rsp8BKC8iE5LoxZbwkwV6CNxrhxhHx68qP2aqIUU52SPucmNBiGUvNuNHGxkWa4TbZ4rOC6AkI3jxtxmKGlCiBpdTaWaB4cY8GWOC5NudJADIAUE X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/19/25 3:24 PM, Harry Yoo wrote: > On Tue, Nov 18, 2025 at 08:11:04PM +0800, Qi Zheng wrote: >> >> >> On 11/18/25 7:28 PM, Qi Zheng wrote: >>> Hi Harry, >>> >>> On 11/17/25 5:17 PM, Harry Yoo wrote: >>>> On Tue, Oct 28, 2025 at 09:58:19PM +0800, Qi Zheng wrote: >>>>> From: Muchun Song >>>>> >>>>> Memory cgroup functions such as get_mem_cgroup_from_folio() and >>>>> get_mem_cgroup_from_mm() return a valid memory cgroup pointer, >>>>> even for the root memory cgroup. In contrast, the situation for >>>>> object cgroups has been different. >>>>> >>>>> Previously, the root object cgroup couldn't be returned because >>>>> it didn't exist. Now that a valid root object cgroup exists, for >>>>> the sake of consistency, it's necessary to align the behavior of >>>>> object-cgroup-related operations with that of memory cgroup APIs. >>>>> >>>>> Signed-off-by: Muchun Song >>>>> Signed-off-by: Qi Zheng >>>>> --- >>>>>   include/linux/memcontrol.h | 29 +++++++++++++++++------- >>>>>   mm/memcontrol.c            | 45 ++++++++++++++++++++------------------ >>>>>   mm/percpu.c                |  2 +- >>>>>   3 files changed, 46 insertions(+), 30 deletions(-) >>>>> >>>>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >>>>> index 6185d8399a54e..9fdbd4970021d 100644 >>>>> --- a/include/linux/memcontrol.h >>>>> +++ b/include/linux/memcontrol.h >>>>> @@ -332,6 +332,7 @@ struct mem_cgroup { >>>>>   #define MEMCG_CHARGE_BATCH 64U >>>>>   extern struct mem_cgroup *root_mem_cgroup; >>>>> +extern struct obj_cgroup *root_obj_cgroup; >>>>>   enum page_memcg_data_flags { >>>>>       /* page->memcg_data is a pointer to an slabobj_ext vector */ >>>>> @@ -549,6 +550,11 @@ static inline bool >>>>> mem_cgroup_is_root(struct mem_cgroup *memcg) >>>>>       return (memcg == root_mem_cgroup); >>>>>   } >>>>> +static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) >>>>> +{ >>>>> +    return objcg == root_obj_cgroup; >>>>> +} >>>> >>>> After reparenting, an objcg may satisfy objcg->memcg == root_mem_cgroup >>>> while objcg != root_obj_cgroup. Should they be considered as >>>> root objcgs? >>> >>> Indeed, it's pointless to charge to root_mem_cgroup (objcg->memcg). >>> >>> So it should be: >>> >>> static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) >>> { >>>     return (objcg == root_obj_cgroup) || (objcg->memcg == >>> root_mem_cgroup); >>> } >> >> Oh, we can't do that because we still need to consider this objcg when >> uncharging. Some pages may be charged before reparenting. > > Ouch, right. We don't know if it's charged before reparenting and so > it can break statistics in a few places if we skip uncharging it after > repareting. Right. > > And I think we don't charge new pages to objcgs that satisfy > (objcg->memcg == root_mem_cgroup) && (objcg != root_obj_cgroup) > after they're reparented anyway... The charge and uncharge operations must be symmetrical, so we cannot control the charge operation independently. Otherwise: charge ====== if ((objcg->memcg == root_mem_cgroup)) skip charge this page uncharge ======== we can't decide whether to skip this page. Thanks, Qi >