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 B63A1CED617 for ; Tue, 18 Nov 2025 12:11:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0C8F26B0096; Tue, 18 Nov 2025 07:11:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0A0F66B0099; Tue, 18 Nov 2025 07:11:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F1F4F6B00A8; Tue, 18 Nov 2025 07:11:26 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id E0E3C6B0096 for ; Tue, 18 Nov 2025 07:11:26 -0500 (EST) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 7F49F13B243 for ; Tue, 18 Nov 2025 12:11:26 +0000 (UTC) X-FDA: 84123612972.11.B53141C Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) by imf09.hostedemail.com (Postfix) with ESMTP id 3BCDB14000E for ; Tue, 18 Nov 2025 12:11:22 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=XWcpFE9b; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf09.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.188 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763467883; a=rsa-sha256; cv=none; b=Vyev9+z92gBP8Sv5qv4RISIfIT4BjfDep8KwkfifKYDVj5SnYZA4ddJfjocp5HuZZ5wftw wA9seaT3WqOfYNMg1titn44IchwZZHRiicJG+SFY27oQexJk436DZscda/348cMXHRsS8d fwqohlQgTc0BZXLYiR78mIv7vpY2xxs= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=XWcpFE9b; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf09.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.188 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1763467883; 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=+lNwnvmSsPR/k/zhjmVCKNI0fGEACpfEUHv6io9dj+U=; b=jp6yzJ9nWfKXjXyh8EvfhTUyNphA/2Mndn0uQyTjHjHd8J7qpWFd8Tx+4ITzDetQyGwAVU FGYg9t8aGP5YucIAVgSTWP9wVPP6O1rNsjYo6jnGzmnAkeKdm3+ZRFnr1/9dFwhc1qXQ2K zaPmQzNQP/PTftFVrjlVBKTIbUs7JH4= Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1763467879; 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=+lNwnvmSsPR/k/zhjmVCKNI0fGEACpfEUHv6io9dj+U=; b=XWcpFE9bHyrL3ur4jyLZUcH0ErcPM8hhnMwadsfGMXehkbuBJdkd1yEAxdN/M1/RLt6XPo JcN2VN7T4K7pbMyfxZEYNiIJp5yCrjNpHytpSb2fgcbYS4zRdFg2rqw9uz8Em1YcLAjVAP LarhuYQHkv5JuvBqxHUwezsqqG6aJug= Date: Tue, 18 Nov 2025 20:11:04 +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-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 3BCDB14000E X-Stat-Signature: zzgwsm1smqbjxdhxquirwjhzaegpaoe3 X-HE-Tag: 1763467882-52795 X-HE-Meta: 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 PcuR6K9T Dg/iUVakcFMuWcGU8McpII976B3JoX4EYIZuWmLGZW3Dz/O01JJFfmLKirg2uWEu26EyRlXl+k3GbXa2wU7mDLWABrP6QNSCJ303JXzJ4W/f4jTTiqQ8OFhPZqe1HRsTW4iCe/voGKP5iDAFxffpPcx1xIkO7+iqljLzoD84FCmFzmSKEOeJakX8tpyJ9VYFc+7iCc8boJqgzQCRXYaKuaVmU82ARVyb9o15WMgVtqwOOo4110+rAk9rDlw== 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 11/18/25 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. > >> >>>   static inline bool mem_cgroup_disabled(void) >>>   { >>>       return !cgroup_subsys_enabled(memory_cgrp_subsys); >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index 2afd7f99ca101..d484b632c790f 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -2871,7 +2865,7 @@ int __memcg_kmem_charge_page(struct page *page, >>> gfp_t gfp, int order) >>>       int ret = 0; >>>       objcg = current_obj_cgroup(); >>> -    if (objcg) { >>> +    if (!obj_cgroup_is_root(objcg)) { >> >> Now that we support the page and slab allocators support allocating >> memory >> in NMI contexts (on some archs), current_obj_cgroup() can return NULL >> if (IS_ENABLED(CONFIG_MEMCG_NMI_UNSAFE) && in_nmi()) returns true >> (then it leads to a NULL-pointer-deref bug). >> >> But IIUC this is applied to kmem charging only (as they use this_cpu ops >> for stats update), and we don't have to apply the same restriction to >> charging LRU pages with objcg. >> >> Maybe Shakeel has more insight on this. >> >> Link: https://lore.kernel.org/all/20250519063142.111219-1- >> shakeel.butt@linux.dev > > Thanks for this information, and it seems there's nothing wrong here. > > Thanks, > Qi > >> >