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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 33120ECDE20 for ; Wed, 11 Sep 2019 16:57:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 131A020863 for ; Wed, 11 Sep 2019 16:57:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729509AbfIKQ47 (ORCPT ); Wed, 11 Sep 2019 12:56:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40118 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729242AbfIKQ46 (ORCPT ); Wed, 11 Sep 2019 12:56:58 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 3947030832E9; Wed, 11 Sep 2019 16:56:58 +0000 (UTC) Received: from [10.10.125.194] (ovpn-125-194.rdu2.redhat.com [10.10.125.194]) by smtp.corp.redhat.com (Postfix) with ESMTP id 36AEA10018F8; Wed, 11 Sep 2019 16:56:56 +0000 (UTC) Subject: Re: [RFC PATCH] Add proc interface to set PF_MEMALLOC flags To: Martin Raiber , "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-block@vger.kernel.org" , Linux-MM References: <20190909162804.5694-1-mchristi@redhat.com> <5D76995B.1010507@redhat.com> <0102016d1f7af966-334f093b-2a62-4baa-9678-8d90d5fba6d9-000000@eu-west-1.amazonses.com> From: Mike Christie Message-ID: <5D792758.2060706@redhat.com> Date: Wed, 11 Sep 2019 11:56:56 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <0102016d1f7af966-334f093b-2a62-4baa-9678-8d90d5fba6d9-000000@eu-west-1.amazonses.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Wed, 11 Sep 2019 16:56:58 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 09/11/2019 03:40 AM, Martin Raiber wrote: > On 10.09.2019 10:35 Damien Le Moal wrote: >> Mike, >> >> On 2019/09/09 19:26, Mike Christie wrote: >>> Forgot to cc linux-mm. >>> >>> On 09/09/2019 11:28 AM, Mike Christie wrote: >>>> There are several storage drivers like dm-multipath, iscsi, and nbd that >>>> have userspace components that can run in the IO path. For example, >>>> iscsi and nbd's userspace deamons may need to recreate a socket and/or >>>> send IO on it, and dm-multipath's daemon multipathd may need to send IO >>>> to figure out the state of paths and re-set them up. >>>> >>>> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the >>>> memalloc_*_save/restore functions to control the allocation behavior, >>>> but for userspace we would end up hitting a allocation that ended up >>>> writing data back to the same device we are trying to allocate for. >>>> >>>> This patch allows the userspace deamon to set the PF_MEMALLOC* flags >>>> through procfs. It currently only supports PF_MEMALLOC_NOIO, but >>>> depending on what other drivers and userspace file systems need, for >>>> the final version I can add the other flags for that file or do a file >>>> per flag or just do a memalloc_noio file. >> Awesome. That probably will be the perfect solution for the problem we hit with >> tcmu-runner a while back (please see this thread: >> https://www.spinics.net/lists/linux-fsdevel/msg148912.html). >> >> I think we definitely need nofs as well for dealing with cases where the backend >> storage for the user daemon is a file. >> >> I will give this patch a try as soon as possible (I am traveling currently). >> >> Best regards. > > I had issues with this as well, and work on this is appreciated! In my > case it is a loop block device on a fuse file system. > Setting PF_LESS_THROTTLE was the one that helped the most, though, so > add an option for that as well? I set this via prctl() for the thread > calling it (was easiest to add to). > > Sorry, I have no idea about the current rationale, but wouldn't it be > better to have a way to mask a set of block devices/file systems not to > write-back to in a thread. So in my case I'd specify that the fuse > daemon threads cannot write-back to the file system and loop device > running on top of the fuse file system, while all other block > devices/file systems can be write-back to (causing less swapping/OOM > issues). I'm not sure I understood you. The storage daemons I mentioned normally kick off N threads per M devices. The threads handle duties like IO and error handling for those devices. Those threads would set the flag, so those IO/error-handler related operations do not end up writing back to them. So it works similar to how storage drivers work in the kernel where iscsi_tcp has an xmit thread and that does memalloc_noreclaim_save. Only the threads for those specific devices being would set the flag. In your case, it sounds like you have a thread/threads that would operate on multiple devices and some need the behavior and some do not. Is that right?