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 X-Spam-Level: X-Spam-Status: No, score=-7.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62510C433B4 for ; Mon, 3 May 2021 14:20:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3337661166 for ; Mon, 3 May 2021 14:20:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229489AbhECOVP (ORCPT ); Mon, 3 May 2021 10:21:15 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:39679 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229472AbhECOVP (ORCPT ); Mon, 3 May 2021 10:21:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620051621; 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=Cba/OYMboyUL2DtaynOpgQ1aSITP9mKlivymjF+E18U=; b=UIlH1z66YclXqc7gb/oqkfT7ByDetsN+PhHsWQDy8kFJDVtHsmNwlJqWCSRN/csWOfomxQ 8vS7S+zrmGiSghqVnlOyVRoJNAtZLe8U9DwOz5YWZHpPjeOeCjG9jlLTq218CLeerP+o4G htGScNxIP5PLZU7hK/VBbLKk21CfDvs= Received: from mail-qt1-f198.google.com (mail-qt1-f198.google.com [209.85.160.198]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-386-LH9RI_i-PxOERfOC4X5How-1; Mon, 03 May 2021 10:20:20 -0400 X-MC-Unique: LH9RI_i-PxOERfOC4X5How-1 Received: by mail-qt1-f198.google.com with SMTP id 1-20020aed31010000b029019d1c685840so1510032qtg.3 for ; Mon, 03 May 2021 07:20:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:subject:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=Cba/OYMboyUL2DtaynOpgQ1aSITP9mKlivymjF+E18U=; b=SoDgTgZdbDgO9swEh0zH98HmHjBfkeg6UtsWxeFbTOtR/NBCQuHUbTwQA7gPAddho1 YvB3lflEOooaU/wgZ5nXEUE/cWLK8dfCUOURJj2OaOphNjLohmcxt3sVcF3H+wr1g5Rw MFnoJJSY5JU5eB42QPH2G3ToGNjHft/g9bbBu+fpyO2tkY7o/Q2I+Rhia7B3ofNEOK9p lhhrk45BVlHeGYq1mCK2MfYN+lqkmElluJcpT/THROsFpDcqXDiQ8nDiVxRX2kLp9mTE tcM5lpZ2WU1/G1jpxSzG0FnWnsk3gCEVWf6P3YeW2pc4cAOMPwMTANjbOegD0OyiBAe7 ZzHQ== X-Gm-Message-State: AOAM531LQzOxzhKpdvkUFUrOnhXPvKa7RiNr+/Jv5yCh3EUY3I9Q1Vi2 8WoIofxz/jqD6X7q+q7tEilQynBBdC/BgGZBeHQFgQdwO8yBfLhVqnvh4OjU2GT4OiW2ve7DY/G VSTLQ/bfl5x8SQhap0cY+o3zF X-Received: by 2002:a05:622a:15c6:: with SMTP id d6mr16903561qty.172.1620051619877; Mon, 03 May 2021 07:20:19 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxRarG4Zi4peWlqgXlLk5yiZcgOvrdkvZtDmZ1mwnE32A43M0N16VhKdpPc8PH6nbBYcwoXwQ== X-Received: by 2002:a05:622a:15c6:: with SMTP id d6mr16903539qty.172.1620051619684; Mon, 03 May 2021 07:20:19 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id v10sm8614891qtf.39.2021.05.03.07.20.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 May 2021 07:20:19 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH 2/2] mm: memcg/slab: Don't create unfreeable slab To: Vlastimil Babka , Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Shakeel Butt Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org References: <20210502180755.445-1-longman@redhat.com> <20210502180755.445-2-longman@redhat.com> <699e5ac8-9044-d664-f73f-778fe72fd09b@suse.cz> Message-ID: <4c90cf79-9c61-8964-a6fd-2da087893339@redhat.com> Date: Mon, 3 May 2021 10:20:17 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <699e5ac8-9044-d664-f73f-778fe72fd09b@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/3/21 8:22 AM, Vlastimil Babka wrote: > On 5/2/21 8:07 PM, Waiman Long wrote: >> The obj_cgroup array (memcg_data) embedded in the page structure is >> allocated at the first instance an accounted memory allocation happens. >> With the right size object, it is possible that the allocated obj_cgroup >> array comes from the same slab that requires memory accounting. If this >> happens, the slab will never become empty again as there is at least one >> object left (the obj_cgroup array) in the slab. >> >> With instructmentation code added to detect this situation, I got 76 >> hits on the kmalloc-192 slab when booting up a test kernel on a VM. >> So this can really happen. >> >> To avoid the creation of these unfreeable slabs, a check is added to >> memcg_alloc_page_obj_cgroups() to detect that and double the size >> of the array in case it happens to make sure that it comes from a >> different kmemcache. >> >> This change, however, does not completely eliminate the presence >> of unfreeable slabs which can still happen if a circular obj_cgroup >> array dependency is formed. > Hm this looks like only a half fix then. > I'm afraid the proper fix is for kmemcg to create own set of caches for the > arrays. It would also solve the recursive kfree() issue. Right, this is a possible solution. However, the objcg pointers array should need that much memory. Creating its own set of kmemcaches may seem like an overkill. Cheers, Longman