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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 83B45C43441 for ; Sat, 24 Nov 2018 00:04:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4821620865 for ; Sat, 24 Nov 2018 00:04:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4821620865 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728097AbeKXKuY (ORCPT ); Sat, 24 Nov 2018 05:50:24 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:45292 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727607AbeKXKuY (ORCPT ); Sat, 24 Nov 2018 05:50:24 -0500 Received: from localhost.localdomain (c-24-6-170-16.hsd1.ca.comcast.net [24.6.170.16]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id F0555415; Sat, 24 Nov 2018 00:04:05 +0000 (UTC) Date: Fri, 23 Nov 2018 16:04:04 -0800 From: Andrew Morton To: Michal Hocko Cc: , Oscar Salvador , Baoquan He , LKML , Michal Hocko Subject: Re: [RFC PATCH 1/5] mm: print more information about mapping in __dump_page Message-Id: <20181123160404.259413e56a8cc9a22112712a@linux-foundation.org> In-Reply-To: <20181107101830.17405-2-mhocko@kernel.org> References: <20181107101830.17405-1-mhocko@kernel.org> <20181107101830.17405-2-mhocko@kernel.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 7 Nov 2018 11:18:26 +0100 Michal Hocko wrote: > From: Michal Hocko > > __dump_page prints the mapping pointer but that is quite unhelpful > for many reports because the pointer itself only helps to distinguish > anon/ksm mappings from other ones (because of lowest bits > set). Sometimes it would be much more helpful to know what kind of > mapping that is actually and if we know this is a file mapping then also > try to resolve the dentry name. > > ... > > --- a/mm/debug.c > +++ b/mm/debug.c > > ... > > @@ -70,6 +71,18 @@ void __dump_page(struct page *page, const char *reason) > if (PageCompound(page)) > pr_cont(" compound_mapcount: %d", compound_mapcount(page)); > pr_cont("\n"); > + if (PageAnon(page)) > + pr_emerg("anon "); > + else if (PageKsm(page)) > + pr_emerg("ksm "); > + else if (mapping) { > + pr_emerg("%ps ", mapping->a_ops); > + if (mapping->host->i_dentry.first) { > + struct dentry *dentry; > + dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias); > + pr_emerg("name:\"%*s\" ", dentry->d_name.len, dentry->d_name.name); > + } > + } There has to be a better way of printing the filename. It is so often needed. The (poorly named and gleefully undocumented) take_dentry_name_snapshot() looks promising. However it's unclear that __dump_page() is always called from contexts where take_dentry_name_snapshot() and release_dentry_name_snapshot() can be safely called. Probably it's OK, but how to guarantee it?