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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1E4DEC48BD5 for ; Tue, 25 Jun 2019 08:25:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DBED0216C8 for ; Tue, 25 Jun 2019 08:25:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730204AbfFYIZz (ORCPT ); Tue, 25 Jun 2019 04:25:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51954 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726951AbfFYIZy (ORCPT ); Tue, 25 Jun 2019 04:25:54 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BCD49309175F; Tue, 25 Jun 2019 08:25:53 +0000 (UTC) Received: from [10.36.117.83] (ovpn-117-83.ams2.redhat.com [10.36.117.83]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1DBB9600C7; Tue, 25 Jun 2019 08:25:48 +0000 (UTC) Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory To: Oscar Salvador , akpm@linux-foundation.org Cc: mhocko@suse.com, dan.j.williams@intel.com, pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190625075227.15193-1-osalvador@suse.de> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: <2ebfbd36-11bd-9576-e373-2964c458185b@redhat.com> Date: Tue, 25 Jun 2019 10:25:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190625075227.15193-1-osalvador@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Tue, 25 Jun 2019 08:25:54 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.06.19 09:52, Oscar Salvador wrote: > Hi, > > It has been while since I sent previous version [1]. > > In this version I added some feedback I got back then, like letting > the caller decide whether he wants allocating per memory block or > per memory range (patch#2), and having the chance to disable vmemmap when > users want to expose all hotpluggable memory to userspace (patch#5). > > [Testing] > > While I could test last version on powerpc, and Huawei's fellows helped me out > testing it on arm64, this time I could only test it on x86_64. > The codebase is quite the same, so I would not expect surprises. > > - x86_64: small and large memblocks (128MB, 1G and 2G) > - Kernel module that adds memory spanning multiple memblocks > and remove that memory in a different granularity. > > So far, only acpi memory hotplug uses the new flag. > The other callers can be changed depending on their needs. > > Of course, more testing and feedback is appreciated. > > [Coverletter] > > This is another step to make memory hotplug more usable. The primary > goal of this patchset is to reduce memory overhead of the hot-added > memory (at least for SPARSEMEM_VMEMMAP memory model). The current way we use > to populate memmap (struct page array) has two main drawbacks: Mental note: How will it be handled if a caller specifies "Allocate memmap from hotadded memory", but we are running under SPARSEMEM where we can't do this. > > a) it consumes an additional memory until the hotadded memory itself is > onlined and > b) memmap might end up on a different numa node which is especially true > for movable_node configuration. > > a) it is a problem especially for memory hotplug based memory "ballooning" > solutions when the delay between physical memory hotplug and the > onlining can lead to OOM and that led to introduction of hacks like auto > onlining (see 31bc3858ea3e ("memory-hotplug: add automatic onlining > policy for the newly added memory")). > > b) can have performance drawbacks. > > Another minor case is that I have seen hot-add operations failing on archs > because they were running out of order-x pages. > E.g On powerpc, in certain configurations, we use order-8 pages, > and given 64KB base pagesize, that is 16MB. > If we run out of those, we just fail the operation and we cannot add > more memory. At least for SPARSEMEM, we fallback to vmalloc() to work around this issue. I haven't looked into the populate_section_memmap() internals yet. Can you point me at the code that performs this allocation? > We could fallback to base pages as x86_64 does, but we can do better. > > One way to mitigate all these issues is to simply allocate memmap array > (which is the largest memory footprint of the physical memory hotplug) > from the hot-added memory itself. SPARSEMEM_VMEMMAP memory model allows > us to map any pfn range so the memory doesn't need to be online to be > usable for the array. See patch 3 for more details. > This feature is only usable when CONFIG_SPARSEMEM_VMEMMAP is set. > > [Overall design]: > > Implementation wise we reuse vmem_altmap infrastructure to override > the default allocator used by vmemap_populate. Once the memmap is > allocated we need a way to mark altmap pfns used for the allocation. > If MHP_MEMMAP_{DEVICE,MEMBLOCK} flag was passed, we set up the layout of the > altmap structure at the beginning of __add_pages(), and then we call > mark_vmemmap_pages(). > > The flags are either MHP_MEMMAP_DEVICE or MHP_MEMMAP_MEMBLOCK, and only differ > in the way they allocate vmemmap pages within the memory blocks. > > MHP_MEMMAP_MEMBLOCK: > - With this flag, we will allocate vmemmap pages in each memory block. > This means that if we hot-add a range that spans multiple memory blocks, > we will use the beginning of each memory block for the vmemmap pages. > This strategy is good for cases where the caller wants the flexiblity > to hot-remove memory in a different granularity than when it was added. > > MHP_MEMMAP_DEVICE: > - With this flag, we will store all vmemmap pages at the beginning of > hot-added memory. > > So it is a tradeoff of flexiblity vs contigous memory. > More info on the above can be found in patch#2. > > Depending on which flag is passed (MHP_MEMMAP_DEVICE or MHP_MEMMAP_MEMBLOCK), > mark_vmemmap_pages() gets called at a different stage. > With MHP_MEMMAP_MEMBLOCK, we call it once we have populated the sections > fitting in a single memblock, while with MHP_MEMMAP_DEVICE we wait until all > sections have been populated. > > mark_vmemmap_pages() marks the pages as vmemmap and sets some metadata: > > The current layout of the Vmemmap pages are: > > [Head->refcount] : Nr sections used by this altmap > [Head->private] : Nr of vmemmap pages > [Tail->freelist] : Pointer to the head page > > This is done to easy the computation we need in some places. > E.g: > > Example 1) > We hot-add 1GB on x86_64 (memory block 128MB) using > MHP_MEMMAP_DEVICE: > > head->_refcount = 8 sections > head->private = 4096 vmemmap pages > tail's->freelist = head > > Example 2) > We hot-add 1GB on x86_64 using MHP_MEMMAP_MEMBLOCK: > > [at the beginning of each memblock] > head->_refcount = 1 section > head->private = 512 vmemmap pages > tail's->freelist = head > > We have the refcount because when using MHP_MEMMAP_DEVICE, we need to know > how much do we have to defer the call to vmemmap_free(). > The thing is that the first pages of the hot-added range are used to create > the memmap mapping, so we cannot remove those first, otherwise we would blow up > when accessing the other pages. So, assuming we add_memory(1GB, MHP_MEMMAP_DEVICE) and then remove_memory(128MB) of the added memory, this will work? add_memory(8GB, MHP_MEMMAP_DEVICE) For 8GB, we will need exactly 128MB of memmap if I did the math right. So exactly one section. This section will still be marked as being online (although not pages on it are actually online)? > > What we do is that since when we hot-remove a memory-range, sections are being > removed sequentially, we wait until we hit the last section, and then we free > the hole range to vmemmap_free backwards. > We know that it is the last section because in every pass we > decrease head->_refcount, and when it reaches 0, we got our last section. > > We also have to be careful about those pages during online and offline > operations. They are simply skipped, so online will keep them > reserved and so unusable for any other purpose and offline ignores them > so they do not block the offline operation. I assume that they will still be dumped normally by user space. (as they are described by a "memory resource" and not PG_Offline) > > One thing worth mention is that vmemmap pages residing in movable memory is not a > show-stopper for that memory to be offlined/migrated away. > Vmemmap pages are just ignored in that case and they stick around until sections > referred by those vmemmap pages are hot-removed. > > [1] https://patchwork.kernel.org/cover/10875017/ > > Oscar Salvador (5): > drivers/base/memory: Remove unneeded check in > remove_memory_block_devices > mm,memory_hotplug: Introduce MHP_VMEMMAP_FLAGS > mm,memory_hotplug: Introduce Vmemmap page helpers > mm,memory_hotplug: allocate memmap from the added memory range for > sparse-vmemmap > mm,memory_hotplug: Allow userspace to enable/disable vmemmap > > arch/arm64/mm/mmu.c | 5 +- > arch/powerpc/mm/init_64.c | 7 ++ > arch/s390/mm/init.c | 6 ++ > arch/x86/mm/init_64.c | 10 +++ > drivers/acpi/acpi_memhotplug.c | 2 +- > drivers/base/memory.c | 41 +++++++++-- > drivers/dax/kmem.c | 2 +- > drivers/hv/hv_balloon.c | 2 +- > drivers/s390/char/sclp_cmd.c | 2 +- > drivers/xen/balloon.c | 2 +- > include/linux/memory_hotplug.h | 31 ++++++++- > include/linux/memremap.h | 2 +- > include/linux/page-flags.h | 34 +++++++++ > mm/compaction.c | 7 ++ > mm/memory_hotplug.c | 152 ++++++++++++++++++++++++++++++++++------- > mm/page_alloc.c | 22 +++++- > mm/page_isolation.c | 14 +++- > mm/sparse.c | 93 +++++++++++++++++++++++++ > mm/util.c | 2 + > 19 files changed, 394 insertions(+), 42 deletions(-) > Thanks for doing this, this will be very helpful :) -- Thanks, David / dhildenb