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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 82BA7C5475B for ; Fri, 1 Mar 2024 15:42:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 880166B0075; Fri, 1 Mar 2024 10:42:22 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 82FEA6B0078; Fri, 1 Mar 2024 10:42:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6A9DA6B007B; Fri, 1 Mar 2024 10:42:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 5996C6B0075 for ; Fri, 1 Mar 2024 10:42:22 -0500 (EST) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 0DAF01A146A for ; Fri, 1 Mar 2024 15:42:22 +0000 (UTC) X-FDA: 81848886924.09.2DACEBC Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf08.hostedemail.com (Postfix) with ESMTP id D1D6C16000B for ; Fri, 1 Mar 2024 15:42:19 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=JgAyt3+k; spf=pass (imf08.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1709307740; a=rsa-sha256; cv=none; b=g+KVT4L0BEKq6P16IveGQguilAsZCdNRPs2o4S4jDmrZz+0xIwogalXXmB2f6/1nS7MRvZ wsYh78ZEB3Yd5xcI2Qt8am7n9fDvLnti70hqRhKipKLsLzvHd0PwF0RUktK8e/zSMqOV7l Wi38aVTJe5TRMlUIx7iyjdtS++PlelM= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=JgAyt3+k; spf=pass (imf08.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1709307740; h=from:from:sender: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:dkim-signature; bh=+SX6+a+gHTRk/ZHTqi0733lmOobFj9BBLt4v5RFZDFM=; b=OceUTZNdVxY8ak34dfMp6klbFC0zNDjVxfzI0/63BHE5IH9O8UKdLN4jxYbJazHkM0zUJZ p6SXT4XKLrngkbdhOOn5wVm3JxKIOzHSH1ao5pW3PkBcLOIFXVfNc4cssNyso06RgNeIFY b/Kj0S5Uai/2H9bq1D/DSROCLjv0930= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709307739; 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=+SX6+a+gHTRk/ZHTqi0733lmOobFj9BBLt4v5RFZDFM=; b=JgAyt3+ks6Gvh8pY2CthQgDYOBxR5PsD2oOm2IiPMGhVmQ1OtRGFmstaVFtvXAe2f3b8tN d16Zmn1YKoz9Zew1hZmb5M6kjv4iaPcV7snxKTeOPpqAiq1P37GzrTjTVyAkSjyY3GeQTZ pz/JJgmjHh/pKuD/AMx45pnBOeFggjc= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-59-54wiGB8tOl2qCxeFH7gIsg-1; Fri, 01 Mar 2024 10:42:16 -0500 X-MC-Unique: 54wiGB8tOl2qCxeFH7gIsg-1 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-40e40126031so12459865e9.0 for ; Fri, 01 Mar 2024 07:42:16 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1709307735; x=1709912535; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :references:cc:to:content-language:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=+SX6+a+gHTRk/ZHTqi0733lmOobFj9BBLt4v5RFZDFM=; b=dSVlooP63o9c0R3GEprCdmr6mCT37u3qgpK3QcXzLaQj3eV9LlHqhRvCgst9VHBIaH zbUvg+zfAZVttXSwwMBeoKOux9ZfBTPYP8s995yF9yHh87d9meOwzfkaRz8XM86S7vDi 6jypbctqqoJ0Ycs1s8I9pyfrS90b4aT3wbM2E8ePX6V2e9Myy5LvPCaqJIwN6Mo5IBD8 ATE3MAV8uEUTREggGTzGSrSrCQ1c+k3A1OtknRXDJQklzNtQEH4znMJb7iqX6hmrmav6 C/98Bg441pF9RvimWqdMImySxOJYe9EFi+T/WrElixiWEBEduTgf1cUxidHEdc595BdA r2fQ== X-Forwarded-Encrypted: i=1; AJvYcCWt3dRfiiQ5+0gCtij3YHBLQME4FYnFe9aZ1Cjf+KSidR5jtu3Egw8toOvI/DO/VTaQwtl1ZHh13PPoddCqWM0eWdo= X-Gm-Message-State: AOJu0YzOiEYqg1waJAvP+FMJl8Lw1/LaqEwEuEUv+bJ34YM8uY0fsGX2 di8eTDw80jSfi6l5QTIO661+N5Luu5YxENG1YCr8+l8/7UroGYjsKgGvCmj7kMCu7//ni7Wu2Qh LE9nZczp5PsNBrJGB1pKCaKIeF7FwA5Bxw/UexzwmsexUxFRD X-Received: by 2002:a05:600c:19d4:b0:412:b7a6:72bf with SMTP id u20-20020a05600c19d400b00412b7a672bfmr1682450wmq.3.1709307735363; Fri, 01 Mar 2024 07:42:15 -0800 (PST) X-Google-Smtp-Source: AGHT+IFHNyn7lEzkwag1G+wAaMMV62hQHGjCwNOgt5/J/4aLoOZ9yfuPhh7MgBy8z9hlcCWB+/s5DQ== X-Received: by 2002:a05:600c:19d4:b0:412:b7a6:72bf with SMTP id u20-20020a05600c19d400b00412b7a672bfmr1682429wmq.3.1709307734930; Fri, 01 Mar 2024 07:42:14 -0800 (PST) Received: from ?IPV6:2003:cb:c713:3200:77d:8652:169f:b5f7? (p200300cbc7133200077d8652169fb5f7.dip0.t-ipconnect.de. [2003:cb:c713:3200:77d:8652:169f:b5f7]) by smtp.gmail.com with ESMTPSA id k40-20020a05600c1ca800b00412b643b5a3sm5799183wms.11.2024.03.01.07.42.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Mar 2024 07:42:14 -0800 (PST) Message-ID: <4c748e61-7f0a-4681-a2c9-48347a700ba7@redhat.com> Date: Fri, 1 Mar 2024 16:42:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Chapter Three] THP HVO: bring the hugeTLB feature to THP To: Yang Shi , Yu Zhao Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, Jonathan Corbet References: <20240229183436.4110845-1-yuzhao@google.com> <20240229183436.4110845-4-yuzhao@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW 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/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/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 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D1D6C16000B X-Stat-Signature: 9imwe17k5o1wbdk9d6ajxqjwd3ksn1w6 X-Rspam-User: X-HE-Tag: 1709307739-569107 X-HE-Meta: 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 cV7T/bN4 RXNLYUhiYg2I7z9DEp7jSJO2lyhlxErDKd4hhS7G6rh6O5c4eM/zesMI8PM55lxNSQGZAv/rwhv/dxaoDwmNtL1KkbvjE8iepdmZnQJ7uRPsicTLxzenRLCrH4rVKlxoSQERtBYUQA0Q0bRzfPgM+RG4YYDstqmPNRifL 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: List-Subscribe: List-Unsubscribe: On 29.02.24 23:54, Yang Shi wrote: > On Thu, Feb 29, 2024 at 10:34 AM Yu Zhao wrote: >> >> HVO can be one of the perks for heavy THP users like it is for hugeTLB >> users. For example, if such a user uses 60% of physical memory for 2MB >> THPs, THP HVO can reduce the struct page overhead by half (60% * 7/8 >> ~= 50%). >> >> ZONE_NOMERGE considerably simplifies the implementation of HVO for >> THPs, since THPs from it cannot be split or merged and thus do not >> require any correctness-related operations on tail pages beyond the >> second one. >> >> If a THP is mapped by PTEs, two optimization-related operations on its >> tail pages, i.e., _mapcount and PG_anon_exclusive, can be binned to >> track a group of pages, e.g., eight pages per group for 2MB THPs. The >> estimation, as the copying cost incurred during shattering, is also by >> design, since mapping by PTEs is another discouraged behavior. > > I'm confused by this. Can you please elaborate a little bit about > binning mapcount and PG_anon_exclusive? > > For mapcount, IIUC, for example, when inc'ing a subpage's mapcount, > you actually inc the (i % 64) page's mapcount (assuming THP size is 2M > and base page size is 4K, so 8 strides and 64 pages in each stride), > right? But how you can tell each page of the 8 pages has mapcount 1 or > one page is mapped 8 times? Or this actually doesn't matter, we don't > even care to distinguish the two cases? I'm hoping we won't need such elaborate approaches that make the mapcounts even more complicated in the future. Just like for hugetlb HGM (if it ever becomes real), I'm hoping that we can just avoid subpage mapcounts completely, at least in some kernel configs initially. I was looking into having only a single PAE bit this week, but migration+swapout are (again) giving me a really hard time. In theory it's simple, the corner cases are killing me. What I really dislike about PAE right now is not necessarily the space, but that they reside in multiple cachelines and that we have to use atomic operations to set/clear them simply because other page flags might be set concurrently. PAE can only be set/cleared while holding the page table lock already, so I really want to avoid atomics. I have not given up on a single PAE bit per folio, but the alternative I was thinking about this week was simply allocating the space required for maintaining them and storing a pointer to that in the (anon) folio. Not perfect. -- Cheers, David / dhildenb