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=-6.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, 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 F101CC433DF for ; Wed, 29 Jul 2020 13:04:38 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A5FC0206D4 for ; Wed, 29 Jul 2020 13:04:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MRX/JKxI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A5FC0206D4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 39BC36B0006; Wed, 29 Jul 2020 09:04:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 348696B0007; Wed, 29 Jul 2020 09:04:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1EA128D0001; Wed, 29 Jul 2020 09:04:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0088.hostedemail.com [216.40.44.88]) by kanga.kvack.org (Postfix) with ESMTP id 07F936B0006 for ; Wed, 29 Jul 2020 09:04:38 -0400 (EDT) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id B4211182FB208 for ; Wed, 29 Jul 2020 13:04:37 +0000 (UTC) X-FDA: 77091132594.13.earth00_39012cf26f72 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin13.hostedemail.com (Postfix) with ESMTP id F200F18021869 for ; Wed, 29 Jul 2020 13:04:29 +0000 (UTC) X-HE-Tag: earth00_39012cf26f72 X-Filterd-Recvd-Size: 11044 Received: from us-smtp-delivery-74.mimecast.com (us-smtp-delivery-74.mimecast.com [63.128.21.74]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Wed, 29 Jul 2020 13:03:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596027796; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=ehYWEdiPCInDna3ZEshNEs9eA6ojK3scxoagbYtds0c=; b=MRX/JKxIj05ZhxEp3ndOWQOJDMTTYQv/HIvTE8yJNeFbihLjj0wLdg3eE2nRAeFf5WGMAQ mfIR9YLZPqybRQusEiDM75OBGlNrq3pL6ixOUZyT8chzpcoe62tza46CljzGsExKkKq2lH 4g8BvZS4fSlcI2vCe8YzmYXi6KcyFsY= 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-218-zfIkg4DEPruShdJQz36tMw-1; Wed, 29 Jul 2020 09:03:14 -0400 X-MC-Unique: zfIkg4DEPruShdJQz36tMw-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 285C6102C7ED; Wed, 29 Jul 2020 13:03:11 +0000 (UTC) Received: from [10.36.113.153] (ovpn-113-153.ams2.redhat.com [10.36.113.153]) by smtp.corp.redhat.com (Postfix) with ESMTP id 348341001B2C; Wed, 29 Jul 2020 13:03:05 +0000 (UTC) Subject: Re: [RFC PATCH 0/6] decrease unnecessary gap due to pmem kmem alignment To: Mike Rapoport Cc: Justin He , Dan Williams , Vishal Verma , Catalin Marinas , Will Deacon , Greg Kroah-Hartman , "Rafael J. Wysocki" , Dave Jiang , Andrew Morton , Steve Capper , Mark Rutland , Logan Gunthorpe , Anshuman Khandual , Hsin-Yi Wang , Jason Gunthorpe , Dave Hansen , Kees Cook , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-nvdimm@lists.01.org" , "linux-mm@kvack.org" , Wei Yang , Pankaj Gupta , Ira Weiny , Kaly Xin References: <20200729033424.2629-1-justin.he@arm.com> <20200729093150.GC3672596@linux.ibm.com> <20200729130025.GD3672596@linux.ibm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63W5Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAjwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat GmbH Message-ID: <170d7861-4df8-ecaf-dbdd-9e9a4a832f8f@redhat.com> Date: Wed, 29 Jul 2020 15:03:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200729130025.GD3672596@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Rspamd-Queue-Id: F200F18021869 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 Content-Transfer-Encoding: quoted-printable 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 29.07.20 15:00, Mike Rapoport wrote: > On Wed, Jul 29, 2020 at 11:35:20AM +0200, David Hildenbrand wrote: >> On 29.07.20 11:31, Mike Rapoport wrote: >>> Hi Justin, >>> >>> On Wed, Jul 29, 2020 at 08:27:58AM +0000, Justin He wrote: >>>> Hi David >>>>>> >>>>>> Without this series, if qemu creates a 4G bytes nvdimm device, we = can >>>>> only >>>>>> use 2G bytes for dax pmem(kmem) in the worst case. >>>>>> e.g. >>>>>> 240000000-33fdfffff : Persistent Memory >>>>>> We can only use the memblock between [240000000, 2ffffffff] due to= the >>>>> hard >>>>>> limitation. It wastes too much memory space. >>>>>> >>>>>> Decreasing the SECTION_SIZE_BITS on arm64 might be an alternative,= but >>>>> there >>>>>> are too many concerns from other constraints, e.g. PAGE_SIZE, huge= tlb, >>>>>> SPARSEMEM_VMEMMAP, page bits in struct page ... >>>>>> >>>>>> Beside decreasing the SECTION_SIZE_BITS, we can also relax the kme= m >>>>> alignment >>>>>> with memory_block_size_bytes(). >>>>>> >>>>>> Tested on arm64 guest and x86 guest, qemu creates a 4G pmem device= . dax >>>>> pmem >>>>>> can be used as ram with smaller gap. Also the kmem hotplug add/rem= ove >>>>> are both >>>>>> tested on arm64/x86 guest. >>>>>> >>>>> >>>>> Hi, >>>>> >>>>> I am not convinced this use case is worth such hacks (that=E2=80=99= s what it is) >>>>> for now. On real machines pmem is big - your example (losing 50% is >>>>> extreme). >>>>> >>>>> I would much rather want to see the section size on arm64 reduced. = I >>>>> remember there were patches and that at least with a base page size= of 4k >>>>> it can be reduced drastically (64k base pages are more problematic = due to >>>>> the ridiculous THP size of 512M). But could be a section size of 51= 2 is >>>>> possible on all configs right now. >>>> >>>> Yes, I once investigated how to reduce section size on arm64 thought= fully: >>>> There are many constraints for reducing SECTION_SIZE_BITS >>>> 1. Given page->flags bits is limited, SECTION_SIZE_BITS can't be red= uced too >>>> much. >>>> 2. Once CONFIG_SPARSEMEM_VMEMMAP is enabled, section id will not be = counted >>>> into page->flags. >>>> 3. MAX_ORDER depends on SECTION_SIZE_BITS=20 >>>> - 3.1 mmzone.h >>>> #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS >>>> #error Allocator MAX_ORDER exceeds SECTION_SIZE >>>> #endif >>>> - 3.2 hugepage_init() >>>> MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >=3D MAX_ORDER); >>>> >>>> Hence when ARM64_4K_PAGES && CONFIG_SPARSEMEM_VMEMMAP are enabled, >>>> SECTION_SIZE_BITS can be reduced to 27. >>>> But when ARM64_64K_PAGES, given 3.2, MAX_ORDER > 29-16 =3D 13. >>>> Given 3.1 SECTION_SIZE_BITS >=3D MAX_ORDER+15 > 28. So SECTION_SIZE_= BITS can not >>>> be reduced to 27. >>>> >>>> In one word, if we considered to reduce SECTION_SIZE_BITS on arm64, = the Kconfig >>>> might be very complicated,e.g. we still need to consider the case fo= r >>>> ARM64_16K_PAGES. >>> >>> It is not necessary to pollute Kconfig with that. >>> arch/arm64/include/asm/sparesemem.h can have something like >>> >>> #ifdef CONFIG_ARM64_64K_PAGES >>> #define SPARSE_SECTION_SIZE 29 >>> #elif defined(CONFIG_ARM16K_PAGES) >>> #define SPARSE_SECTION_SIZE 28 >>> #elif defined(CONFIG_ARM4K_PAGES) >>> #define SPARSE_SECTION_SIZE 27 >>> #else >>> #error >>> #endif >> >> ack >> >>> =20 >>> There is still large gap with ARM64_64K_PAGES, though. >>> >>> As for SPARSEMEM without VMEMMAP, are there actual benefits to use it= ? >> >> I was asking myself the same question a while ago and didn't really fi= nd >> a compelling one. >=20 > Memory overhead for VMEMMAP is larger, especially for arm64 that knows > how to free empty parts of the memory map with "classic" SPARSEMEM. You mean the hole punching within section memmap? (which is why their pfn_valid() implementation is special) (I do wonder why that shouldn't work with VMEMMAP, or is it simply not implemented?) > =20 >> I think it's always enabled as default (SPARSEMEM_VMEMMAP_ENABLE) and >> would require config tweaks to even disable it. >=20 > Nope, it's right there in menuconfig, >=20 > "Memory Management options" -> "Sparse Memory virtual memmap" Ah, good to know. --=20 Thanks, David / dhildenb