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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F11B4C433FE for ; Mon, 31 Jan 2022 19:01:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358992AbiAaTBh (ORCPT ); Mon, 31 Jan 2022 14:01:37 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60319 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235245AbiAaTBf (ORCPT ); Mon, 31 Jan 2022 14:01:35 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643655695; 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=lxAwEA9Ms4jKsy8aU7wpsx4G3K1ATTggQYOqNKinqIQ=; b=bRvqa2oyRrg1muy2A3fct8z9mQg5YKEVdOo678W9fMhUh1ggJuW+d1PNeoMji/8/JWN/ho hpn3ERFMeC23C7+A1kf3iuGuubSHD70CA2HRaEATjABF8QApGd5026KQE33RKCU02yi1xn 8NV3cboLDzYxpRLTCPA6yZo0iut8NU4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-176-FOuYN5FjP8adVL3IftXX9w-1; Mon, 31 Jan 2022 14:01:31 -0500 X-MC-Unique: FOuYN5FjP8adVL3IftXX9w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7D12D8189FA; Mon, 31 Jan 2022 19:01:29 +0000 (UTC) Received: from [10.22.16.244] (unknown [10.22.16.244]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8CC8360843; Mon, 31 Jan 2022 19:01:19 +0000 (UTC) Message-ID: Date: Mon, 31 Jan 2022 14:01:18 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH v2 3/3] mm/page_owner: Dump memcg information Content-Language: en-US To: Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , Andrew Morton , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Ira Weiny , Rafael Aquini References: <20220129205315.478628-1-longman@redhat.com> <20220129205315.478628-4-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/31/22 04:38, Michal Hocko wrote: > On Sat 29-01-22 15:53:15, Waiman Long wrote: >> It was found that a number of offlined memcgs were not freed because >> they were pinned by some charged pages that were present. Even "echo >> 1 > /proc/sys/vm/drop_caches" wasn't able to free those pages. These >> offlined but not freed memcgs tend to increase in number over time with >> the side effect that percpu memory consumption as shown in /proc/meminfo >> also increases over time. >> >> In order to find out more information about those pages that pin >> offlined memcgs, the page_owner feature is extended to dump memory >> cgroup information especially whether the cgroup is offlined or not. > It is not really clear to me how this is supposed to be used. Are you > really dumping all the pages in the system to find out offline memcgs? > That looks rather clumsy to me. I am not against adding memcg > information to the page owner output. That can be useful in other > contexts. I am just piggybacking on top of the existing page_owner tool to provide information for me to find out what pages are pinning the dead memcgs. page_owner is a debugging tool that is not turned on by default. We do have to add a kernel parameter and  rebooting the system to use that, but that is pretty easy to do once we have a reproducer to reproduce the problem. Cheers, Longman