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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E065BC001DC for ; Thu, 27 Jul 2023 08:35:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232565AbjG0IfO (ORCPT ); Thu, 27 Jul 2023 04:35:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234082AbjG0IeN (ORCPT ); Thu, 27 Jul 2023 04:34:13 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6898949D3 for ; Thu, 27 Jul 2023 01:18:19 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 48ADB1F747; Thu, 27 Jul 2023 08:18:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1690445889; 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=+vEZggNbc6DGoi3i2Ep2+ExdQTZDFALTtNMLWFugNXY=; b=C/77BzXTfBrVPOhMw4lZFYjA2YCLI46gcQbQ+iI259zIdarqgGNQPTDzOzLRyo+Qzp9k9F tzXNzjGyC7J/DVZNdqpbBldFblkGUkzRIeOrXbZK3bO8QWomMOM3Ow7FAtmqBupCY/MasF TMKjyhQzUt0McY0L2n2QgmqqaIas5iY= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 2A4E913902; Thu, 27 Jul 2023 08:18:09 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id q9bpB0EowmS2SgAAMHmgww (envelope-from ); Thu, 27 Jul 2023 08:18:09 +0000 Date: Thu, 27 Jul 2023 10:18:08 +0200 From: Michal Hocko To: David Hildenbrand Cc: Ross Zwisler , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mike Rapoport , Andrew Morton , Matthew Wilcox , Mel Gorman , Vlastimil Babka Subject: Re: collision between ZONE_MOVABLE and memblock allocations Message-ID: References: <20230718220106.GA3117638@google.com> <20230719224821.GC3528218@google.com> <9ef757dc-da4b-9fa1-de84-1328a74f18a7@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9ef757dc-da4b-9fa1-de84-1328a74f18a7@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 26-07-23 10:44:21, David Hildenbrand wrote: > On 20.07.23 00:48, Ross Zwisler wrote: > > On Wed, Jul 19, 2023 at 08:14:48AM +0200, Michal Hocko wrote: > > > On Tue 18-07-23 16:01:06, Ross Zwisler wrote: > > > [...] > > > > I do think that we need to fix this collision between ZONE_MOVABLE and memmap > > > > allocations, because this issue essentially makes the movablecore= kernel > > > > command line parameter useless in many cases, as the ZONE_MOVABLE region it > > > > creates will often actually be unmovable. > > > > > > movablecore is kinda hack and I would be more inclined to get rid of it > > > rather than build more into it. Could you be more specific about your > > > use case? > > > > The problem that I'm trying to solve is that I'd like to be able to get kernel > > core dumps off machines (chromebooks) so that we can debug crashes. Because > > the memory used by the crash kernel ("crashkernel=" kernel command line > > option) is consumed the entire time the machine is booted, there is a strong > > motivation to keep the crash kernel as small and as simple as possible. To > > this end I'm trying to get away without SSD drivers, not having to worry about > > encryption on the SSDs, etc. > > Okay, so you intend to keep the crashkernel area as small as possible. > > > > > So, the rough plan right now is: > > > 1) During boot set aside some memory that won't contain kernel > allocations. > > I'm trying to do this now with ZONE_MOVABLE, but I'm open to better ways. > > > > We set aside memory for a crash kernel & arm it so that the ZONE_MOVABLE > > region (or whatever non-kernel region) will be set aside as PMEM in the crash > > kernel. This is done with the memmap=nn[KMG]!ss[KMG] kernel command line > > parameter passed to the crash kernel. > > > > So, in my sample 4G VM system, I see: > > > > # lsmem --split ZONES --output-all > > RANGE SIZE STATE REMOVABLE BLOCK NODE ZONES > > 0x0000000000000000-0x0000000007ffffff 128M online yes 0 0 None > > 0x0000000008000000-0x00000000bfffffff 2.9G online yes 1-23 0 DMA32 > > 0x0000000100000000-0x000000012fffffff 768M online yes 32-37 0 Normal > > 0x0000000130000000-0x000000013fffffff 256M online yes 38-39 0 Movable > > Memory block size: 128M > > Total online memory: 4G > > Total offline memory: 0B > > > > so I'll pass "memmap=256M!0x130000000" to the crash kernel. > > > > 2) When we hit a kernel crash, we know (hope?) that the PMEM region we've set > > aside only contains user data, which we don't want to store anyway. > > I raised that in different context already, but such assumptions are not > 100% future proof IMHO. For example, we might at one point be able to make > user page tables movable and place them on there. > > But yes, most kernel data structures (which you care about) will probably > never be movable and never end up on these regions. > > > We make a > > filesystem in there, and create a kernel crash dump using 'makedumpfile': > > > > mkfs.ext4 /dev/pmem0 > > mount /dev/pmem0 /mnt > > makedumpfile -c -d 31 /proc/vmcore /mnt/kdump > > > > We then set up the next full kernel boot to also have this same PMEM region, > > using the same memmap kernel parameter. We reboot back into a full kernel. > > > > 3) The next full kernel will be a normal boot with a full networking stack, > > SSD drivers, disk encryption, etc. We mount up our PMEM filesystem, pull out > > the kdump and either store it somewhere persistent or upload it somewhere. We > > can then unmount the PMEM and reconfigure it back to system ram so that the > > live system isn't missing memory. > > > > ndctl create-namespace --reconfig=namespace0.0 -m devdax -f > > daxctl reconfigure-device --mode=system-ram dax0.0 > > > > This is the flow I'm trying to support, and have mostly working in a VM, > > except up until now makedumpfile would crash because all the memblock > > structures it needed were in the PMEM area that I had just wiped out by making > > a new filesystem. :) > > > Thinking out loud (and remembering that some architectures relocate the > crashkernel during kexec, if I am not wrong), maybe the following would also > work and make your setup eventually easier: > > 1) Don't reserve a crashkernel area in the traditional way, instead reserve > that area using CMA. It can be used for MOVABLE allocations. > > 2) Let kexec load the crashkernel+initrd into ordinary memory only > (consuming as much as you would need there). > > 3) On kexec, relocate the crashkernel+initrd into the CMA area (overwriting > any movable data in there) > > 4) In makedumpfile, don't dump any memory that falls into the crashkernel > area. It might already have been overwritten by the second kernel This is more or less what Jiri is looking into. -- Michal Hocko SUSE Labs