From patchwork Wed Sep 16 18:34:07 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 11780471 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A62011580 for ; Wed, 16 Sep 2020 18:36:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83FBD20936 for ; Wed, 16 Sep 2020 18:36:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="H20BSvxB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728069AbgIPSgA (ORCPT ); Wed, 16 Sep 2020 14:36:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:60762 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728139AbgIPSe3 (ORCPT ); Wed, 16 Sep 2020 14:34:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600281267; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=sLvJY4ddiVkXmrX1DSGtp9ToKTJ0eE0I5UImDHKq484=; b=H20BSvxB4bYtW/U0UhZ3jng+SjwXA4mUeb+b3H0n2X7THrPoILFxCryFg9Tn1icVNslQiL XH50pfj426Wvs9FWXhYmRIFi01XVIbxR4eZLIbbaKsom4spZWNkb7RCM4R2ZM0x27LykW1 jeGcZzJg8ihjPXCFIEevfA6OnYeP0Kg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-434-ZNEnBkKoOvCSBnNBYlwABA-1; Wed, 16 Sep 2020 14:34:23 -0400 X-MC-Unique: ZNEnBkKoOvCSBnNBYlwABA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AD33B186DD27; Wed, 16 Sep 2020 18:34:20 +0000 (UTC) Received: from t480s.redhat.com (ovpn-113-190.ams2.redhat.com [10.36.113.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id EE34B19D61; Wed, 16 Sep 2020 18:34:12 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-hyperv@vger.kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org, Andrew Morton , David Hildenbrand , Alexander Duyck , Dave Hansen , Haiyang Zhang , "K. Y. Srinivasan" , Mel Gorman , Michael Ellerman , Michal Hocko , Mike Rapoport , Oscar Salvador , Scott Cheloha , Stephen Hemminger , Vlastimil Babka , Wei Liu , Wei Yang Subject: [PATCH RFC 0/4] mm: place pages to the freelist tail when onling and undoing isolation Date: Wed, 16 Sep 2020 20:34:07 +0200 Message-Id: <20200916183411.64756-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org When adding separate memory blocks via add_memory*() and onlining them immediately, the metadata (especially the memmap) of the next block will be placed onto one of the just added+onlined block. This creates a chain of unmovable allocations: If the last memory block cannot get offlined+removed() so will all dependant ones. We directly have unmovable allocations all over the place. This can be observed quite easily using virtio-mem, however, it can also be observed when using DIMMs. The freshly onlined pages will usually be placed to the head of the freelists, meaning they will be allocated next, turning the just-added memory usually immediately un-removable. The fresh pages are cold, prefering to allocate others (that might be hot) also feels to be the natural thing to do. It also applies to the hyper-v balloon xen-balloon, and ppc64 dlpar: when adding separate, successive memory blocks, each memory block will have unmovable allocations on them - for example gigantic pages will fail to allocate. While the ZONE_NORMAL doesn't provide any guarantees that memory can get offlined+removed again (any kind of fragmentation with unmovable allocations is possible), there are many scenarios (hotplugging a lot of memory, running workload, hotunplug some memory/as much as possible) where we can offline+remove quite a lot with this patchset. a) To visualize the problem, a very simple example: Start a VM with 4GB and 8GB of virtio-mem memory: [root@localhost ~]# lsmem RANGE SIZE STATE REMOVABLE BLOCK 0x0000000000000000-0x00000000bfffffff 3G online yes 0-23 0x0000000100000000-0x000000033fffffff 9G online yes 32-103 Memory block size: 128M Total online memory: 12G Total offline memory: 0B Then try to unplug as much as possible using virtio-mem. Observe which memory blocks are still around. Without this patch set: [root@localhost ~]# lsmem RANGE SIZE STATE REMOVABLE BLOCK 0x0000000000000000-0x00000000bfffffff 3G online yes 0-23 0x0000000100000000-0x000000013fffffff 1G online yes 32-39 0x0000000148000000-0x000000014fffffff 128M online yes 41 0x0000000158000000-0x000000015fffffff 128M online yes 43 0x0000000168000000-0x000000016fffffff 128M online yes 45 0x0000000178000000-0x000000017fffffff 128M online yes 47 0x0000000188000000-0x0000000197ffffff 256M online yes 49-50 0x00000001a0000000-0x00000001a7ffffff 128M online yes 52 0x00000001b0000000-0x00000001b7ffffff 128M online yes 54 0x00000001c0000000-0x00000001c7ffffff 128M online yes 56 0x00000001d0000000-0x00000001d7ffffff 128M online yes 58 0x00000001e0000000-0x00000001e7ffffff 128M online yes 60 0x00000001f0000000-0x00000001f7ffffff 128M online yes 62 0x0000000200000000-0x0000000207ffffff 128M online yes 64 0x0000000210000000-0x0000000217ffffff 128M online yes 66 0x0000000220000000-0x0000000227ffffff 128M online yes 68 0x0000000230000000-0x0000000237ffffff 128M online yes 70 0x0000000240000000-0x0000000247ffffff 128M online yes 72 0x0000000250000000-0x0000000257ffffff 128M online yes 74 0x0000000260000000-0x0000000267ffffff 128M online yes 76 0x0000000270000000-0x0000000277ffffff 128M online yes 78 0x0000000280000000-0x0000000287ffffff 128M online yes 80 0x0000000290000000-0x0000000297ffffff 128M online yes 82 0x00000002a0000000-0x00000002a7ffffff 128M online yes 84 0x00000002b0000000-0x00000002b7ffffff 128M online yes 86 0x00000002c0000000-0x00000002c7ffffff 128M online yes 88 0x00000002d0000000-0x00000002d7ffffff 128M online yes 90 0x00000002e0000000-0x00000002e7ffffff 128M online yes 92 0x00000002f0000000-0x00000002f7ffffff 128M online yes 94 0x0000000300000000-0x0000000307ffffff 128M online yes 96 0x0000000310000000-0x0000000317ffffff 128M online yes 98 0x0000000320000000-0x0000000327ffffff 128M online yes 100 0x0000000330000000-0x000000033fffffff 256M online yes 102-103 Memory block size: 128M Total online memory: 8.1G Total offline memory: 0B With this patch set: [root@localhost ~]# lsmem RANGE SIZE STATE REMOVABLE BLOCK 0x0000000000000000-0x00000000bfffffff 3G online yes 0-23 0x0000000100000000-0x000000013fffffff 1G online yes 32-39 Memory block size: 128M Total online memory: 4G Total offline memory: 0B All memory can get unplugged, all memory block can get removed. Of course, no workload ran and the system was basically idle, but it highlights the issue - the fairly deterministic chain of unmovable allocations. When a huge page for the 2MB memmap is needed, a just-onlined 4MB page will be split. The remaining 2MB page will be used for the memmap of the next memory block. So one memory block will hold the memmap of the two following memory blocks. Finally the pages of the last-onlined memory block will get used for the next bigger allocations - if any allocation is unmovable, all dependent memory blocks cannot get unplugged and removed until that allocation is gone. Note that with bigger memory blocks (e.g., 256MB), *all* memory blocks are dependent and none can get unplugged again! b) Experiment with memory intensive workload I performed an experiment with an older version of this patch set (before we used undo_isolate_page_range() in online_pages(): Hotplug 56GB to a VM with an initial 4GB, onlining all memory to ZONE_NORMAL right from the kernel when adding it. I then run various memory intensive workloads that consume most system memory for a total of 45 minutes. Once finished, I try to unplug as much memory as possible. With this change, I am able to remove via virtio-mem (adding individual 128MB memory blocks) 413 out of 448 added memory blocks. Via individual (256MB) DIMMs 380 out of 448 added memory blocks. (I don't have any numbers without this patchset, but looking at the above example, it's at most half of the 448 memory blocks for virtio-mem, and most probably none for DIMMs). Again, there are workloads that might behave very differently due to the nature of ZONE_NORMAL. c) Future work: - I'll be looking into avoiding reporting freshly onlined pages via the free page reporting framework. They are unbacked in the hypervisor, so reporting them isn't necessary (and might actually be bad for performance in some future use cases in the hypervisor). - I'll be looking into being able to tell the OS that some pages are fresh (e.g., via alloc_contig_range() in virito-mem, freeing balloon inflated memory in a ballooning driver), such that we will skip reporting them via free page reporting (marking them reported), and placing them to the tail of the freelist. - virtio-mem will soon also support ZONE_MOVABLE, however, especially when hotplugging a lot of memory (as in the experiment), a considerable amount of memory will have to remain in ZONE_NORMAL - so this change is relevant in any case. I'm sending this as RFC as it also in its current form for simplicity affects not only memory onlining but also - Other users of undo_isolate_page_range(): Pages are always placed to the tail. -- When memory offlining fails -- When memory isolation fails after having isolated some pageblocks -- When alloc_contig_range() either succeeds or fails - Other users of __putback_isolated_page(): Pages are always placed to the tail. -- Free page reporting - Other users of __free_pages_core() -- AFAIKs, any memory that is getting exposed to the buddy during boot. IIUC we will now usually allocate memory from lower addresses within a zone first (especially during boot). - Other users of generic_online_page() -- Hyper-V balloon Let's see if there are concerns for these users with this approach. David Hildenbrand (4): mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag mm/page_alloc: place pages to tail in __putback_isolated_page() mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate() mm/page_alloc: place pages to tail in __free_pages_core() include/linux/page-isolation.h | 2 + mm/page_alloc.c | 102 +++++++++++++++++++++++++-------- mm/page_isolation.c | 8 ++- 3 files changed, 86 insertions(+), 26 deletions(-)