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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 B1E52C2D0E4 for ; Tue, 24 Nov 2020 08:20:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 06F4A208DB for ; Tue, 24 Nov 2020 08:20:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="hUYh/iU/" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 06F4A208DB Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 092126B005D; Tue, 24 Nov 2020 03:20:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 043546B006E; Tue, 24 Nov 2020 03:20:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E99346B0070; Tue, 24 Nov 2020 03:20:07 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0044.hostedemail.com [216.40.44.44]) by kanga.kvack.org (Postfix) with ESMTP id A10586B005D for ; Tue, 24 Nov 2020 03:20:07 -0500 (EST) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 147E78249980 for ; Tue, 24 Nov 2020 08:20:07 +0000 (UTC) X-FDA: 77518614054.06.lift48_130d5a42736c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin06.hostedemail.com (Postfix) with ESMTP id E06F51003FB24 for ; Tue, 24 Nov 2020 08:20:06 +0000 (UTC) X-HE-Tag: lift48_130d5a42736c X-Filterd-Recvd-Size: 6909 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Tue, 24 Nov 2020 08:20:06 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1606206005; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=roLXjPdZSyjfxbswfdmyz8HZsNkniy24pO6y4bkuN5M=; b=hUYh/iU/cU/7AByPIn0H+ed3kCXycS7U6l5BBvy1UqzcmeahB//kcSwkqjQt4u1K1qA65A SgmuKgeIX/aVUUo4fF9xiushJ8vkPAp1GFvLFE9q0RPKeeyMsT5SAuDSuz7h4YKyc5N0DH s8c5tYTDuxkrMm3q5FGee29WHFLyZ7g= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E9150AF58; Tue, 24 Nov 2020 08:20:04 +0000 (UTC) Date: Tue, 24 Nov 2020 09:20:03 +0100 From: Michal Hocko To: Pavel Tatashin Cc: linux-mm , Andrew Morton , Vlastimil Babka , LKML , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , Joonsoo Kim , sthemmin@microsoft.com Subject: Re: Pinning ZONE_MOVABLE pages Message-ID: <20201124081837.GS27488@dhcp22.suse.cz> References: <20201123090129.GD27488@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Mon 23-11-20 11:06:21, Pavel Tatashin wrote: > On Mon, Nov 23, 2020 at 4:01 AM Michal Hocko wrote: > > > > On Fri 20-11-20 15:27:46, Pavel Tatashin wrote: > > > Recently, I encountered a hang that is happening during memory hot > > > remove operation. It turns out that the hang is caused by pinned user > > > pages in ZONE_MOVABLE. > > > > > > Kernel expects that all pages in ZONE_MOVABLE can be migrated, but > > > this is not the case if a user applications such as through dpdk > > > libraries pinned them via vfio dma map. > > > > Long term or effectively time unbound pinning on zone movable is > > fundamentaly broken. The sole reason of ZONE_MOVABLE existence is to > > guarantee migrateability. If the cosumer of this memory cannot guarantee > > that then it shouldn't use __GFP_MOVABLE in the first place. > > Exactly, this is what I am trying to solve, and started this thread to > figure out what is the best approach to address this problem. > > > > > > Kernel keeps trying to > > > hot-remove them, but refcnt never gets to zero, so we are looping > > > until the hardware watchdog kicks in. > > > > Yeah, the existing offlining behavior doesn't stop trying because the > > current implementation of the migration cannot tell a diffence between > > short and long term failures. Maybe the recent ref count for long term > > pinning can be used to help out there. > > > > Anyway, I am wondering what do you mean by watchdog firing. The > > operation should trigger neither of soft, hard or hung detectors. > > You are right, the hot-remove is killable operation. In our case, > however, systemd stops petting watchdog during kexec reboot to ensure > that reboot finishes, however, because we hot-remove memory during > shutdown, and kernel is unable to hot-remove memory within 60s we get > a watchdog reset. Well, this should be worked around quite trivially. You can kill your attempt before the timeout fires. [...] > > > 2. Add an internal move_pages_zone() similar to move_pages() syscall > > > but instead of migrating to a different NUMA node, migrate pages from > > > ZONE_MOVABLE to another zone. > > > Call move_pages_zone() on demand prior to pinning pages from > > > vfio_pin_map_dma() for instance. > > > > Why is the existing migration API insufficient? > > Here I am talking about internal implementation not user API. We do > not have a function that migrates pages in a user address space from > one zone to another zone. We only have a function that is exposed as a > syscall that migrates pages from one node to another node. We do have migrate_pages and its interface should make it trivial enough that a new general purpose helper shouldn't be really needed. struct migration_target_control mtc = { .gfp_mask = GFP_USER | __GFP_RETRY_MAYFAIL, }; migrate_pages(&list_of_pages, alloc_migration_target, NULL, (unsigned long)&mtc, MIGRATE_SYNC, MR_PINNING); note that NR_PINNING would have to added. > > > 3. Perhaps, it also makes sense to add madvise() flag, to allocate > > > pages from non-movable zone. When a user application knows that it > > > will do DMA mapping, and pin pages for a long time, the memory that it > > > allocates should never be migrated or hot-removed, so make sure that > > > it comes from the appropriate place. > > > The benefit of adding madvise() flag is that we won't have to deal > > > with slow page migration during pin time, but the disadvantage is that > > > we would need to change the user interface. > > > > No, the MOVABLE_ZONE like other zone types are internal implementation > > detail of the MM. I do not think we want to expose that to the userspace > > and carve this into stone. > > What I mean here is allowing users to guarantee that the page's PA is > going to stay the same. Sort of a stronger mlock. Mlock only > guarantees that the page is not swapped, but something like > MADV_PINNED would guarantee that page is not going to be swapped and > also not migrated. There were some discussions around vmpin/unpin syscalls. This didn't really lead anywhere. One of the roadblock was a proper accounting IIRC. You might want to look for those discussions in email archives. > If a user determines the PA of that page, that PA > is going to stay the same throughout the life of the page. This is not > exposing internal implementation in any way, this guarantee could be > honored in various ways: i.e. pinned or allocating from ZONE_NORMAL. > The fact that we would honor it by allocating memory from ZONE_NORMAL > is implementation detail that would not be exposed to the user. Jason has already replied to this and I do not have much to add. [...] > I just think it is inefficient to first allocate memory from > ZONE_MOVABLE, and later migrate it to ZONE_NORMAL. Yes it is inefficient. Is it usual that the memory is already faulted in when it is pinned? -- Michal Hocko SUSE Labs