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 4858EC7EE30 for ; Wed, 25 Jun 2025 08:53:50 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DE8256B00A1; Wed, 25 Jun 2025 04:53:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D98AC6B00A3; Wed, 25 Jun 2025 04:53:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C60F06B00A8; Wed, 25 Jun 2025 04:53:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id B4C306B00A1 for ; Wed, 25 Jun 2025 04:53:49 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 4155ABF7CB for ; Wed, 25 Jun 2025 08:53:49 +0000 (UTC) X-FDA: 83593310178.04.40050C8 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf02.hostedemail.com (Postfix) with ESMTP id C606180004 for ; Wed, 25 Jun 2025 08:53:46 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dK1bHUrK; spf=pass (imf02.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1750841626; 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=0e8BoDLq196flVUDfV/vvRQXSzcbFa8gqqzTgNqKOzQ=; b=YB9N1BoC7L8sPxhldazHy6D30JY0tCkumRV7Upyr/CoaVyB/G6L/yBbiGdiLYRGr24NcGm Wb2XG/7QJRiddTGUC7yNADFlfJal8KhlH9YC7aLa8YmQDDliy31kHupAXM+acAHBPhMUiZ dD6hzNSbd4tbEGGzAnR5UBqxzJ/7xAw= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dK1bHUrK; spf=pass (imf02.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1750841626; a=rsa-sha256; cv=none; b=ow6VTxginG/9fzgvNf4gzBzLgrWizUVE5RpuH+M9lBzUFThQWx/odZ2l2fw7nE67Rrx/tr UzoW6jzG7HESvUzO6fu7U6ZhvBi5WT8lFgMjW9O+Mxu3N+mgabo26/ZpZAIoInYBW8CRTJ 5eI91urbM7xZwsi/JnlIjHmM3+RuZU8= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1750841626; 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=0e8BoDLq196flVUDfV/vvRQXSzcbFa8gqqzTgNqKOzQ=; b=dK1bHUrKlc32zIIVaBNojibLhBXvYsnxWNDbh9Oz0Nvha+jMPtPRSQ2fRKijWdRkXQWV1m rEsAfQcGv6q6fjcoizryWS2ezsuYhKEq8raMV3o7lG0iMU6wsFEOSVYq50hQ8p48pwCuLu LnWEkF1BNci5i24dx+MZaeOhv4z0Z1Y= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-619-EM38KpDaPs66khe_HL9rTg-1; Wed, 25 Jun 2025 04:53:44 -0400 X-MC-Unique: EM38KpDaPs66khe_HL9rTg-1 X-Mimecast-MFC-AGG-ID: EM38KpDaPs66khe_HL9rTg_1750841623 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-450eaae2934so53551805e9.2 for ; Wed, 25 Jun 2025 01:53:44 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1750841623; x=1751446423; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=0e8BoDLq196flVUDfV/vvRQXSzcbFa8gqqzTgNqKOzQ=; b=oJFc+yt4A/KIEYYJkyOoxV0tiBOM9kgXObMK+uXJbWYHg16xmPF+UpqJOZG1U4otfC V2P6vY5jLCscPgnJDTBLlBMVTKrns846lF2ASkWCL3eH7lFXOy8j1D2hwunHaBtLLyXE DCbX1ujcEE91eK9PnbnPpSskMhG+e56o4BJmf6SmEmdl8kEBeOrx0Ndqy0+I6IQChKCY 6hxC2Psnl3LnhBPYoi04WSfis6/M6/c01WZPEvjwmA+HHpxci4zAVq2NQCmIDfoAj0Dx P10kGUZakDhtc5887b2OtHX8ASJ9dVWfY4UnatEJGqfPc5ElThqZ3oTsWwHtWvitEjRw TJSw== X-Forwarded-Encrypted: i=1; AJvYcCVWMyfKB/utPQQL+epa71DAR6fTJjBwxu8/BqcNRoUoqfvNRYG9vYQDTDRTORw0gKM9K2XeI6+9qg==@kvack.org X-Gm-Message-State: AOJu0YxWxlIpmdFU8rRbQrAIPRyP7XijGilC4/j69c/hYJfVv6goS5U8 8kH+fz1NFMJ+IE5v6yowMz8Xpx2+CWnFljCmfvxYC5lXLLdNzxmrAQUbT5Ir5zz0EIM8Dfk1HRp axLZqqLr2RNxuf3ZxOY5rXSP/+1ENRW/kHB1TbmQBOXX6J0WLbbZh X-Gm-Gg: ASbGncsuEJQHS4ZFaUqiEuT7XSIGTulczecffw7MmVA8KJjgGQMMCxUhpNsN+qS4u0/ sLNd/lWqYH6ITKobvDKYnM5fHPdaKBbkpnng6fvNjZ/BpuiR4EsmunG2CCh3yHDWABQtIyyib13 nUTP3LZ/TAn70Jj3cmqmN1vNDWuuzMJpuTxtKsQMyPgjayJKjd/wd+MCemTSO1IqYGCfGUBrnD2 cTgssdje/wb0+FK3LIY7p0sqjVeLRUwQ+ITOT+w6kqV2WL6hLKqgnokiLDqRVNWPtrRoZRBD7uJ yQ6GKOnDgIln42WIyesr1Kxk9v3P1Yp2bAllyAQGuUaWhf/xRPMlKv4iLyVGQSG2tW+Ked/a0f5 AD9IZyeV0kWt32sRXD5Ma9WyfGaQ795EiTGocUqKOJ47r X-Received: by 2002:a05:600c:8b45:b0:450:d01f:de6f with SMTP id 5b1f17b1804b1-45381ab000fmr19392065e9.15.1750841623130; Wed, 25 Jun 2025 01:53:43 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFTv4HpJcoINB6om+LOfg/ajMyM1672zXm+Tupck3O8L0NlZXsrLq6TKOv12mKFQuOe6uHP9Q== X-Received: by 2002:a05:600c:8b45:b0:450:d01f:de6f with SMTP id 5b1f17b1804b1-45381ab000fmr19391785e9.15.1750841622733; Wed, 25 Jun 2025 01:53:42 -0700 (PDT) Received: from ?IPV6:2003:d8:2f12:1b00:5d6b:db26:e2b7:12? (p200300d82f121b005d6bdb26e2b70012.dip0.t-ipconnect.de. [2003:d8:2f12:1b00:5d6b:db26:e2b7:12]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45382362ab2sm13253025e9.25.2025.06.25.01.53.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Jun 2025 01:53:41 -0700 (PDT) Message-ID: <8de73035-8645-4c53-80a5-de63128d388e@redhat.com> Date: Wed, 25 Jun 2025 10:53:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are disabled To: Lorenzo Stoakes Cc: Hugh Dickins , Baolin Wang , akpm@linux-foundation.org, ziy@nvidia.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, zokeefe@google.com, shy828301@gmail.com, usamaarif642@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <75c02dbf-4189-958d-515e-fa80bb2187fc@google.com> <008ec97f-3b33-4b47-a112-9cef8c1d7f58@redhat.com> <01d679f2-fd64-472c-b9dc-ebe87268ce82@lucifer.local> <23b8ad10-cd1f-45df-a25c-78d01c8af44f@redhat.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-MFC-PROC-ID: wxoR0wNV8p5ogsS8rTbyZV7dQ59w6VLJ-j5z3MiBXEQ_1750841623 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C606180004 X-Stat-Signature: qbcrbshr9d46yw6mf13fkeqawgkd7jqc X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1750841626-928767 X-HE-Meta: U2FsdGVkX1+pnsbWc4H+P77+Ug0CQNzJ6wx21b17j0UKt6XlAvg5o2X6LCce5bJII6ytiZYzUi+gRSsrnVgzR70fgPwcR0A2PhFitaUrURYmmegGalWNNKq68Q/SxUC0OT4j0Ddzwu2YtnR9SCB6XM18G6Rbq5OeHNzV8qsL970VqQYQ/9co+GBguag1HvhE6D2WGCb9o7N2+2aVeoxQOI/TWMNeaA4RXwJpO5vi4x0b/1Y5mPdohfnAJQThUDgqqIQmxoD8/ZhH8PSuxUH+k/sY2djIXNcXGxmzAE7OYyFgj2l/Nt7CdnSvLAYCkMgIKggZs3LV5pFyzGJWTVXaVlGoDsGmGspBR81ZiT5tpPoefqMr6kqk4wRjItfwxeK9s+NrBFRDoZZ1nenB9rSFCOXbTmiAikjdOnfnOmd7cMIv8s5kbYpwbV6m0/sLbPTlwG1RgvHvvnjCsXSgwGUJ9bo+bV6kWsk8ZsH0861wpaGJ/MgXYI31GPQodXwW3COjBDOF5SgJb6hkMEaJxUsdZ1BUAaGx6YyWib+zqc7spV12LjK6BGgYgNEhElFD32i5PZqW0zz3y1LTKrePaItnKJRPZi6X4TNZjA5ZINgVMMrDYDQ9bdCg2o2rOujwue3/uJESQubeM1WmXGGrfhFm65eKE6xCuRVMQ63hfEFQaH1YmXb0hN8C5BrZhmh9fbjoqYnw6MWirtNvbiR35BUA60QOuW24XCRsrfjjsdskEpAEJjn36J007LVwuHSZOKxFJ5ytHMHw+RarDoUysUcKPUMLuObgyyBTzX9FdhE7yBBuSGLrYyy/SeO5YbyJNCv6dDLjDud5apHhnm52wBNItPZbbe082gAV2bxFbWPuNlmcGiVWOEgFOfiFHWqOEIsAn5Lz6qH0mS1ZIemTeq00+ykoTutUqXw07ldv8Ju4tDdxAaw2MFYTigrykeW/pM1PT/yukxTZGW+D3jiW/jo XHyPihf/ CiIgeVt34ZkzFe6iJ0udYrjnXdc/wBH+a8AvfaH4b61DGMqZ6+kCCOruwc2c2Dr7Spel8yGK1O3c3REZ2V0gFR7UMUmwl+TU52s1Xz0BQgbcUVUVj/vJGmm6w6hhnNxGcLRtM+BRGtuEx1k9l/by5l1lAuNO3aE2b4hLnkqhBZyS5iD2UtgL5NZXI0IcAsCm6m3c2nLu71QSUTZiI2IGfjTgrPqdw7qS+9iO5USt6sCO4CEUgNUtVVwIagrW6RhTRHngU8UKTuq0TK/1HW3Ku5dn6KBhdRz2FqfcAcwPrIR4Cv3HQrF0xGqEr+kKj8anpfHTEsju88ZxwT15asNV4GPZzQbHL2fafpe168SrbmCziPoiAYXyDJL0cpZR9SAczOUo72jb6U6EqkQ42na0cA+1JsjJHEiYa8LIutzZ1GKr8pydWuMpOkewycM8PmcpUVb4efJVTrU57KQ4= 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 25.06.25 10:37, Lorenzo Stoakes wrote: > On Wed, Jun 25, 2025 at 10:24:53AM +0200, David Hildenbrand wrote: >> On 25.06.25 10:12, Lorenzo Stoakes wrote: >>> On Wed, Jun 25, 2025 at 08:55:28AM +0100, Lorenzo Stoakes wrote: >>>> I suppose the least awful way of addressing Baolin's concerns re: mTHP >>>> while simultaneosly keeping existing semantics is: >>>> >>>> 1. Introduce deny to mean what never should have meant. >>> >>> To fix Baolin's issue btw we'd have to add 'deny' to both 'global' settings >>> _and_ each page size setting. >>> >>> Because otherwise we'd end up in a weird case where say: >>> >>> global 'deny' >>> >>> 2 MiB 'never' >>> 64 KiB 'inherit' >>> >>> And err... get 2 MiB THP pages from MADV_COLLAPSE :) >>> >>> Or: >>> >>> global 'deny' >>> >>> 2 MiB 'never' >>> 64 KiB 'always' >>> >>> Or: >>> >>> global 'never' >>> >>> 2 MiB 'never' >>> 64 KiB 'always' >>> >>> Or: >>> >>> global 'never' >>> >>> 2 MiB 'madvise' >>> 64 KiB 'always' >>> >>> All doing the same. Not very clear is it? >>> >>> We have sowed the seeds of something terrible here, truly. >> >> Fully agreed. "Deny" is nasty. Maybe if we really need a way to disable >> "madv_collapse", it should be done differently, not using this toggle here. > > Yeah maybe the best way is to just have another tunable for this? > > /sys/kernel/mm/transparent_hugepage/disable_collapse perhaps? > > What do you think Hugh, Baolin? Probably, for debugging purposes, a kernel cmdline option would work as well. Something we can just easily change later. > >> >> Regarding MADV_COLLAPSE, I strongly assume that we should not change it to >> collapse smaller mTHPs as part of the khugepaged mTHP work. For now, it will >> simply always collapse to PMD THPs. > > Yeah thinking about it maybe this is the best way. And we can then update > the man page to make this ABUNDANTLY clear (am happy to do this). > > This keeps things simple. > > (One side note on PMD-sized MADV_COLLAPSE - this is basically completely > useless for 64 KB page size arm64 systems where PMD's are 512 MB :) > > Thoughts Baolin? > >> >> Once we want to support other sizes, likely MADV_COLLAPSE users want to have >> better control over which size to use, at which point it all gets nasty. > > madvise2() this time with extra parameters? ;) > > I sort of wish we had added a flags parameter there. > > But lacking a time machine... :) Reminds me of how MAP_HUGETLB squeezed in the sizes by stealing plenty of bits ... :) -- Cheers, David / dhildenb