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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 631B8C433EF for ; Tue, 8 Feb 2022 18:41:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EF3A36B007E; Tue, 8 Feb 2022 13:41:15 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E7BA66B0080; Tue, 8 Feb 2022 13:41:15 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CF6596B0081; Tue, 8 Feb 2022 13:41:15 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0253.hostedemail.com [216.40.44.253]) by kanga.kvack.org (Postfix) with ESMTP id BE0E76B007E for ; Tue, 8 Feb 2022 13:41:15 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 695EE98797 for ; Tue, 8 Feb 2022 18:41:15 +0000 (UTC) X-FDA: 79120480110.12.5452F34 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf12.hostedemail.com (Postfix) with ESMTP id BA45C40010 for ; Tue, 8 Feb 2022 18:41:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1644345674; 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=xML1xNkIw3e0hTYk74bi0fSg0bcnbMZm5u6L4MPv8BA=; b=bck0yfKicJmKETmL+MCTzBS/qgOqMz1tJSizTsus6ltfq9Cp0UGNPIQn/SEu3tSNynlTHH onTPxwk711oQoqxDMFJJzbycFeZldhZVO8NqtHgGeXsREglZo8IUT2ldqiNSjW1ZZzW1mf WlZHGyi6MUlWPl3tfygVWYmD8iZ8wLk= 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-168-4DGKpYoYNeCJaX4uVE-ldw-1; Tue, 08 Feb 2022 13:41:11 -0500 X-MC-Unique: 4DGKpYoYNeCJaX4uVE-ldw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 10B42101F003; Tue, 8 Feb 2022 18:41:02 +0000 (UTC) Received: from [10.22.35.8] (unknown [10.22.35.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8F62710A3945; Tue, 8 Feb 2022 18:40:58 +0000 (UTC) Message-ID: Date: Tue, 8 Feb 2022 13:40:57 -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 v5 3/4] mm/page_owner: Print 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 , Mike Rapoport , David Rientjes , Roman Gushchin , Rafael Aquini , Mike Rapoport References: <20220208000532.1054311-1-longman@redhat.com> <20220208000532.1054311-4-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Rspamd-Queue-Id: BA45C40010 X-Stat-Signature: ryezzxaysu3zncdjzbpdwg15a75gw3im X-Rspam-User: Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=bck0yfKi; spf=none (imf12.hostedemail.com: domain of longman@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=longman@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam05 X-HE-Tag: 1644345674-333454 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: On 2/8/22 07:13, Michal Hocko wrote: > On Mon 07-02-22 19:05:31, Waiman Long wrote: >> It was found that a number of dying 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 dying >> 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. > I still believe that this is very suboptimal way to debug offline memcgs > but memcg information can be useful in other contexts and it doesn't > cost us anything except for an additional output so I am fine with this. I am planning to have a follow-up patch to add a new debugfs file for just printing page information associated with dying memcgs only. It will be based on the existing page_owner code, though. So I need to get this patch in first. > >> In order to find out more information about those pages that pin >> dying memcgs, the page_owner feature is extended to print memory >> cgroup information especially whether the cgroup is dying or not. >> RCU read lock is taken when memcg is being accessed to make sure >> that it won't be freed. >> >> Signed-off-by: Waiman Long >> Acked-by: David Rientjes >> Acked-by: Roman Gushchin >> Acked-by: Mike Rapoport > With few comments/questions below. > >> --- >> mm/page_owner.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 44 insertions(+) >> >> diff --git a/mm/page_owner.c b/mm/page_owner.c >> index 28dac73e0542..d4c311455753 100644 >> --- a/mm/page_owner.c >> +++ b/mm/page_owner.c >> @@ -10,6 +10,7 @@ >> #include >> #include >> #include >> +#include >> #include >> >> #include "internal.h" >> @@ -325,6 +326,47 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m, >> seq_putc(m, '\n'); >> } >> >> +/* >> + * Looking for memcg information and print it out >> + */ > I am not sure this is particularly useful comment. Right, I can remove that. > >> +static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, >> + struct page *page) >> +{ >> +#ifdef CONFIG_MEMCG >> + unsigned long memcg_data; >> + struct mem_cgroup *memcg; >> + bool dying; >> + >> + rcu_read_lock(); >> + memcg_data = READ_ONCE(page->memcg_data); >> + if (!memcg_data) >> + goto out_unlock; >> + >> + if (memcg_data & MEMCG_DATA_OBJCGS) >> + ret += scnprintf(kbuf + ret, count - ret, >> + "Slab cache page\n"); >> + >> + memcg = page_memcg_check(page); >> + if (!memcg) >> + goto out_unlock; >> + >> + dying = (memcg->css.flags & CSS_DYING); > Is there any specific reason why you haven't used mem_cgroup_online? Not really. However, I think checking for CSS_DYING makes more sense now that I using the term "dying". > >> + ret += scnprintf(kbuf + ret, count - ret, >> + "Charged %sto %smemcg ", >> + PageMemcgKmem(page) ? "(via objcg) " : "", >> + dying ? "dying " : ""); >> + >> + /* Write cgroup name directly into kbuf */ >> + cgroup_name(memcg->css.cgroup, kbuf + ret, count - ret); >> + ret += strlen(kbuf + ret); > cgroup_name should return the length of the path added to the buffer. I realized that after I sent out the patch. I will remove te redundant strlen() in a future update. > >> + ret += scnprintf(kbuf + ret, count - ret, "\n"); > I do not see any overflow prevention here. I believe you really need to > check ret >= count after each scnprintf/cgroup_name. As you have realized, the beauty of using scnprintf() is to not needing an overflow check after each invocation. Cheers, Longman