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=-7.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS,USER_AGENT_MUTT 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 1AC2FC169C4 for ; Mon, 11 Feb 2019 16:49:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DACC921B68 for ; Mon, 11 Feb 2019 16:49:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727299AbfBKQtU (ORCPT ); Mon, 11 Feb 2019 11:49:20 -0500 Received: from koef.zs64.net ([212.12.50.230]:13427 "EHLO koef.zs64.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726105AbfBKQtU (ORCPT ); Mon, 11 Feb 2019 11:49:20 -0500 X-Greylist: delayed 1255 seconds by postgrey-1.27 at vger.kernel.org; Mon, 11 Feb 2019 11:49:18 EST Received: from koef.zs64.net (koef.zs64.net [212.12.50.230]) by 0ons.org (8.15.2/8.15.2) with ESMTP id x1BGSMM4048139 for ; Mon, 11 Feb 2019 16:28:22 GMT (envelope-from cracauer@koef.zs64.net) Received: (from cracauer@localhost) by koef.zs64.net (8.15.2/8.15.2/Submit) id x1BGSMJd048136 for linux-kernel@vger.kernel.org; Mon, 11 Feb 2019 11:28:22 -0500 (EST) (envelope-from cracauer) Date: Mon, 11 Feb 2019 11:28:22 -0500 From: Martin Cracauer To: linux-kernel@vger.kernel.org Subject: Possibe NFS mm problem: client page-in errors with ZFS Linux server Message-ID: <20190211162821.GA38018@cons.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.11.2 (2019-01-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Folks. I suspect that this isn't actually a ZFS bug but a general memory manager problem. I would appreciate input from mm folks. I parked the detailed bug report here for now: https://github.com/zfsonlinux/zfs/issues/8396 Short story: When running a ZFS on a Linux 4.19/4.20 NFS server the clients are occasionally unsuccessful in perfectly normal page-in on mapped files. Example: executable on NFS mounted filesystem. Some executable-mapped page is referenced. The page is supposed to be retrieved on demand if not resident yet. This occasionally fails with recent Linux or ZoL code. The semantics of the error are identical to what is legitimately happening when you have a page fault in a NFS client mapped file after that file has been unlinked on the server side. Here it is happening without the unlinking. I suspect this might be a general Linux mm problem because I cross-checked with a FreeBSD server with very similar ZFS code. Although I cannot track when the error started appearing I know it is about within the last 6 months and I read all commits to ZoL that manage pages and couldn't see anything suspicious off-hand. On the other hand the errors do not appear when moving the server side file tree to ext4fs. The errors get more frequent with uptime of the server and are not impressed by drop_caches or by trying to evict ZFS' own caches with memory pressure. Details with a line of reasoning why I blame the server and all other info I am collecting: https://github.com/zfsonlinux/zfs/issues/8396 Thanks Martin -- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Martin Cracauer http://www.cons.org/cracauer/