From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99E5830147C for ; Fri, 22 Aug 2025 14:10:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755871846; cv=none; b=Ocd+cLz9Pm2OMhVSeKDJnBGwks/O78yuWvNGwpF7NPe2AGQqkdbrtPjq5yjb9ftEiDJjk4VBbDHDSbcNNi1Ztb6xfzfvfcb13C7hiENmETARQYsha0vcttAjDB/yhuMCCUeWSfGkw8g6pI7yfy3OlqfP7qrJePx/p9jZYizeuHQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755871846; c=relaxed/simple; bh=G2WxCv6oiSFA+ItejNsR+Qf2E8pYgoeEr8WbwSgPY3Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Gt7zcTmi64IZ1A/u5FKbY22wpDREGqd1UNPD7/1xMCjCDXzSDpniCp+vEn1+lRagCnMSnHhrbfUXz5XBcG8ekd961aO7JaWJeAHhrigQjaPhJMSvZ7ltgreQiFgQlvQWhs8AJjeAJOvIPr1U2TG4wdA/b7yNg6tx/hF40oepJCg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=hrjp0Hqy; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hrjp0Hqy" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755871843; 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=y4Sy5j6GyLKa/6POtPURBhOkK7kt59z0IbjXNHFAuis=; b=hrjp0HqyDfAXOoFLztpK9LPzIaUc23Y6bPOsof5ZUXEU0LyEjz4BFKG5MEVfcUtFq37Uai XE0j1nr3smhcXJsKlHphNE1H4tJ9xOqVNVRsl7qyQWxyYyYXzPlkHiEzWgJyNEHIyAjx6W WPx7xbSkz4rt364/Ggdy96L0KNW0cZM= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-516-NJjzIixOPCeZmKTM70bB3w-1; Fri, 22 Aug 2025 10:10:40 -0400 X-MC-Unique: NJjzIixOPCeZmKTM70bB3w-1 X-Mimecast-MFC-AGG-ID: NJjzIixOPCeZmKTM70bB3w_1755871839 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-3b9dc5c2c7dso862473f8f.1 for ; Fri, 22 Aug 2025 07:10:40 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1755871839; x=1756476639; h=content-transfer-encoding:in-reply-to: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=y4Sy5j6GyLKa/6POtPURBhOkK7kt59z0IbjXNHFAuis=; b=FLXtyXGZjm2O9Riz+Wo3bjeVs+QNx8iB8rft9kyosEss/FAQf5Ja9qnLHEMdBYrfF/ Xy5LhyTeZ5rLMFX7uT9hmLbvLK0u6pZHdeFub9gcHDAWTL9DvRiBFtHL/5yLsGTNhWmp Ev8TX+eYWjO90W77vQV0UXddowTsrFrvznhFFuJMrMYzUl5Mw9K3AWnQ/UQwh57LFr3P kDpEROCERH42kzz6wi7Gpboru5g0Pl7ch1sUx5I9aharA6gWUngG9bPPl+H4sg7M1h+D +p1Fk5AS204CinBGyXUJUD8D51U1h9+TR7oMLw/3F+w0JwFCVHhskIWZ/dMhbBrw2mxL HXiQ== X-Forwarded-Encrypted: i=1; AJvYcCWsfldlWgCXPpRopTt2ISueW4td9PvTRSqzTQVvp14XJ/rYCaX2JN6rdvPKc1SLRO+6L6hhm80K7cseG0aSlW1Srlg=@vger.kernel.org X-Gm-Message-State: AOJu0YxNdenodKuFfLUsZY7qauBwGTb+6AEgWmSwHcvVCh300mclsXAz 0VpSjtIwuCuJqPS8mwxqclRsBI4JQQBiHYYJp7pJ9rX4iiOUW7i1D1b8TRlNoka1cbEH0d2ijmq 4cMhiy1xKuOdTO6AC0VpQT3cdlgPj74Wwf4qG+opQELsO7FsezGvEmaQ4pl0JfWmZWvJd0cetr4 yp9GUXdQ== X-Gm-Gg: ASbGncuovbs5kpKWg+CYB6VttG+JymbrrtcHCmUWwIM5JtzZ5yhaYjJrEbn2SRPuklx MbmtNdxtnvjhRtkxiGJIcmGduFEkJ2xCqa3M4kWw93hDt/cyx7oX2cF5lSgzJafrhl8Mzp6zYio +RUogXnVHNrhPI7b+9toqYDMG30KIQMNkkMkw9Tg/UnrTaBAAg+75QkPbGoWKHMiQJNRcBCa43t WNYNuGYItTibP22aE/yAe+mFhifCsjzZAi4eHLnn2ReHUqEaA5EaefT4CKJEFkdljnZUib5jXEZ WSKHYJJKTQbe5VFaMoLp4AtxRRAfLvmJpM3+2ynggtHcvaNzPw4uJB3I6rbPNR8k1bEFjiNauMu A84A2jc4Gda4U4bGwzQN8FdZ7dzz8D+xaIVWwDquY4PthliDWafELiNSHN0mTV0sVWgw= X-Received: by 2002:a05:6000:40dd:b0:3c3:973a:fe40 with SMTP id ffacd0b85a97d-3c5de349863mr2850216f8f.58.1755871838817; Fri, 22 Aug 2025 07:10:38 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGG3zymBLgr0oFAq5QBoFCFU2lzOHhnQpA7QCSr+J+SBt8FHvbVBMdDQMGrrRZe6+dP4YZONw== X-Received: by 2002:a05:6000:40dd:b0:3c3:973a:fe40 with SMTP id ffacd0b85a97d-3c5de349863mr2850174f8f.58.1755871838314; Fri, 22 Aug 2025 07:10:38 -0700 (PDT) Received: from ?IPV6:2003:d8:2f2e:6100:d9da:ae87:764c:a77e? (p200300d82f2e6100d9daae87764ca77e.dip0.t-ipconnect.de. [2003:d8:2f2e:6100:d9da:ae87:764c:a77e]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3c077c576b7sm15322771f8f.63.2025.08.22.07.10.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Aug 2025 07:10:37 -0700 (PDT) Message-ID: Date: Fri, 22 Aug 2025 16:10:35 +0200 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 00/13] khugepaged: mTHP support To: Lorenzo Stoakes Cc: Nico Pache , Dev Jain , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kirill.shutemov@linux.intel.com, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com References: <20250819134205.622806-1-npache@redhat.com> <38b37195-28c8-4471-bd06-951083118efd@arm.com> <0d9c6088-536b-4d7a-8f75-9be5f0faa86f@lucifer.local> <5bea5efa-2efc-4c01-8aa1-a8711482153c@lucifer.local> <95012dfc-d82d-4ae2-b4cd-1e8dcf15e44b@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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: K7UowuOOQWp2s47prVrJWzi7oz0sqtkOFOXfe6cdsMI_1755871839 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit >> Once could also easily support the value 255 (HPAGE_PMD_NR / 2- 1), but not sure >> if we have to add that for now. > > Yeah not so sure about this, this is a 'just have to know' too, and yes you > might add it to the docs, but people are going to be mightily confused, esp if > it's a calculated value. > > I don't see any other way around having a separate tunable if we don't just have > something VERY simple like on/off. Yeah, not advocating that we add support for other values than 0/511, really. > > Also the mentioned issue sounds like something that needs to be fixed elsewhere > honestly in the algorithm used to figure out mTHP ranges (I may be wrong - and > happy to stand corrected if this is somehow inherent, but reallly feels that > way). I think the creep is unavoidable for certain values. If you have the first two pages of a PMD area populated, and you allow for at least half of the #PTEs to be non/zero, you'd collapse first a order-2 folio, then and order-3 ... until you reached PMD order. So for now we really should just support 0 / 511 to say "don't collapse if there are holes" vs. "always collapse if there is at least one pte used". > >> >> Because, as raised in the past, I'm afraid nobody on this earth has a clue how >> to set this parameter to values different to 0 (don't waste memory with khugepaged) >> and 511 (page fault behavior). > > Yup > >> >> >> If any other value is set, essentially >> pr_warn("Unsupported 'max_ptes_none' value for mTHP collapse"); >> >> for now and just disable it. > > Hmm but under what circumstances? I would just say unsupported value not mention > mTHP or people who don't use mTHP might find that confusing. Well, we can check whether any mTHP size is enabled while the value is set to something unexpected. We can then even print the problematic sizes if we have to. We could also just just say that if the value is set to something else than 511 (which is the default), it will be treated as being "0" when collapsing mthp, instead of doing any scaling. -- Cheers David / dhildenb