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,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 B0FE8C46466 for ; Mon, 5 Oct 2020 17:28:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61DF42068D for ; Mon, 5 Oct 2020 17:28:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FCYbIhIb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727872AbgJER2J (ORCPT ); Mon, 5 Oct 2020 13:28:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:37678 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725815AbgJER2I (ORCPT ); Mon, 5 Oct 2020 13:28:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601918886; 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=lSWHQWzEWi59CuzC1QSviMVku4FeVT7YUGL5LuM7qH8=; b=FCYbIhIbh2wtMz4LlMY2UTsfA+3i3UU3L13aPP/3qJJxIqvOt4HtrIjjerrPBhBjskctcP UqIxlKubK4LfVJldCtGjvGxmwAWm/a7xz61GclrMyAVHrkJNf4y9jEro4dTbX3fOicgjRc RYPsni12vynnMIETWpoAzu74SbKBmtM= 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-285-twRPEbUuOLeO25Kg6HvyBA-1; Mon, 05 Oct 2020 13:28:02 -0400 X-MC-Unique: twRPEbUuOLeO25Kg6HvyBA-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id C219E85B686; Mon, 5 Oct 2020 17:27:52 +0000 (UTC) Received: from [10.36.112.79] (ovpn-112-79.ams2.redhat.com [10.36.112.79]) by smtp.corp.redhat.com (Postfix) with ESMTP id 753F778800; Mon, 5 Oct 2020 17:27:48 +0000 (UTC) Subject: Re: [RFC PATCH v2 00/30] 1GB PUD THP support on x86_64 To: Roman Gushchin , Zi Yan Cc: Michal Hocko , linux-mm@kvack.org, "Kirill A . Shutemov" , Rik van Riel , Matthew Wilcox , Shakeel Butt , Yang Shi , Jason Gunthorpe , Mike Kravetz , William Kucharski , Andrea Arcangeli , John Hubbard , David Nellans , linux-kernel@vger.kernel.org References: <20200928175428.4110504-1-zi.yan@sent.com> <20200930115505.GT2277@dhcp22.suse.cz> <73394A41-16D8-431C-9E48-B14D44F045F8@nvidia.com> <20201002073205.GC20872@dhcp22.suse.cz> <9a7600e2-044a-50ca-acde-bf647932c751@redhat.com> <20201002081023.GA4555@dhcp22.suse.cz> <645b35a5-970d-dcfe-2b4a-04ebd4444756@redhat.com> <20201005171632.GB2990415@carbon.DHCP.thefacebook.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: Date: Mon, 5 Oct 2020 19:27:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20201005171632.GB2990415@carbon.DHCP.thefacebook.com> 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.10.20 19:16, Roman Gushchin wrote: > On Mon, Oct 05, 2020 at 11:03:56AM -0400, Zi Yan wrote: >> On 2 Oct 2020, at 4:30, David Hildenbrand wrote: >> >>> On 02.10.20 10:10, Michal Hocko wrote: >>>> On Fri 02-10-20 09:50:02, David Hildenbrand wrote: >>>>>>>> - huge page sizes controllable by the userspace? >>>>>>> >>>>>>> It might be good to allow advanced users to choose the page sizes, so they >>>>>>> have better control of their applications. >>>>>> >>>>>> Could you elaborate more? Those advanced users can use hugetlb, right? >>>>>> They get a very good control over page size and pool preallocation etc. >>>>>> So they can get what they need - assuming there is enough memory. >>>>>> >>>>> >>>>> I am still not convinced that 1G THP (TGP :) ) are really what we want >>>>> to support. I can understand that there are some use cases that might >>>>> benefit from it, especially: >>>> >>>> Well, I would say that internal support for larger huge pages (e.g. 1GB) >>>> that can transparently split under memory pressure is a useful >>>> funtionality. I cannot really judge how complex that would be >>> >>> Right, but that's then something different than serving (scarce, >>> unmovable) gigantic pages from CMA / reserved hugetlbfs pool. Nothing >>> wrong about *real* THP support, meaning, e.g., grouping consecutive >>> pages and converting them back and forth on demand. (E.g., 1GB -> >>> multiple 2MB -> multiple single pages), for example, when having to >>> migrate such a gigantic page. But that's very different from our >>> existing gigantic page code as far as I can tell. >> >> Serving 1GB PUD THPs from CMA is a compromise, since we do not want to >> bump MAX_ORDER to 20 to enable 1GB page allocation in buddy allocator, >> which needs section size increase. In addition, unmoveable pages cannot >> be allocated in CMA, so allocating 1GB pages has much higher chance from >> it than from ZONE_NORMAL. > > s/higher chances/non-zero chances Well, the longer the system runs (and consumes a significant amount of available main memory), the less likely it is. > > Currently we have nothing that prevents the fragmentation of the memory > with unmovable pages on the 1GB scale. It means that in a common case > it's highly unlikely to find a continuous GB without any unmovable page. > As now CMA seems to be the only working option. > And I completely dislike the use of CMA in this context (for example, allocating via CMA and freeing via the buddy by patching CMA when splitting up PUDs ...). > However it seems there are other use cases for the allocation of continuous > 1GB pages: e.g. secretfd ( https://lwn.net/Articles/831628/ ), where using > 1GB pages can reduce the fragmentation of the direct mapping. Yes, see RFC v1 where I already cced Mike. > > So I wonder if we need a new mechanism to avoid fragmentation on 1GB/PUD scale. > E.g. something like a second level of pageblocks. That would allow to group > all unmovable memory in few 1GB blocks and have more 1GB regions available for > gigantic THPs and other use cases. I'm looking now into how it can be done. Anything bigger than sections is somewhat problematic: you have to track that data somewhere. It cannot be the section (in contrast to pageblocks) > If anybody has any ideas here, I'll appreciate a lot. I already brought up the idea of ZONE_PREFER_MOVABLE (see RFC v1). That somewhat mimics what CMA does (when sized reasonably), works well with memory hot(un)plug, and is immune to misconfiguration. Within such a zone, we can try to optimize the placement of larger blocks. -- Thanks, David / dhildenb