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 5DA0E2E6CA6 for ; Mon, 1 Sep 2025 16:46:58 +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=1756745220; cv=none; b=iPNl64NYqZe8/xXB8f2kcnzfEJXyyy2koc/ho1HfG33iBHleshirpmSgfjcAo+uz5sx+f2KjaFkCX8YaydeKuM8RcCU0u2Zj6u2a7OKo9cJNK2ydmIHypxu/SgsbeA2mM9JDhaOfPXd3YPv5avD0RbUuJAtMvWPzo3YNZ4PCvJo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756745220; c=relaxed/simple; bh=X0oKnYbiVEjCHGsIrUvYtt0g2xuxFs5OUKmp5O1iF9s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=k7FLSREQw4otJVse2AdIcGGAJ3oXaNdbRYMfOsNsNhLoUWFJmNbkob2QSo6yla1MS2bBeyNB3aon2gvMZzrlm3SXGInlJcz6J5HOWj2y30Cb4ajwdTzHXxZkW2crjTp0MdOln1w3/xKOxwOmxwfg9zrDtIQXBjNXiiz6rGylZWc= 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=WG90rtTS; 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="WG90rtTS" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1756745217; 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=zvn18oPnLd+zvAZSKNse2+rKolpo9zqjbywvQFctj6g=; b=WG90rtTSFubpcPrB6Z+xvjAe0+lMDcBtlPbko3nrRtWOS+7CDM2gVzEHMRP8XGVBXb38GJ PgozvVCVEGB1BWI7XMWcLEig+X0YvY3m+ldsA4aohzzNpeC4qmzWRPPMGGoEcmmcP+IX+S Rg8e+YKU+C87REIdbAxzMXuIO+2Y1fY= 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-656-7kgwbyCZPQyKe3mEchNjUg-1; Mon, 01 Sep 2025 12:46:54 -0400 X-MC-Unique: 7kgwbyCZPQyKe3mEchNjUg-1 X-Mimecast-MFC-AGG-ID: 7kgwbyCZPQyKe3mEchNjUg_1756745213 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-45b920a0c89so2085075e9.2 for ; Mon, 01 Sep 2025 09:46:53 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1756745213; x=1757350013; 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=zvn18oPnLd+zvAZSKNse2+rKolpo9zqjbywvQFctj6g=; b=r/lFHIwrDGTJSuFWI1eFId3XulSRoP349at/ZSO/FcGwWVfuji6aHcUgkZTkqarmTC Xz/E9fI/6/QSJQGgQKY7dagGf3xyYHoyPTE3BlfyFp1A9aZvGJ1DKRA3EXkDd/CbnLwH BXkcOoaxRWussRvE+XPImn5nSaonSJ7WFhd3O4TL1j0N/S7QYW+LX+osNSukx/9X2BBr vOUt11xmGXntnwCo33LYnyHQ+Yr/ERaG336fo/G1Xnqsr5tupxUwZwY6NNv3zWShajek e+UmwcbYbmc1ugMFAI1XMEeAGwpiPswbZ9rRCWryF8eEFcLuHm+cOYqCnG3NWgMN+D8m bo0g== X-Forwarded-Encrypted: i=1; AJvYcCVhgjngYBF0ffPTk+gNGsimyzmLw1vuk3Q2ONTgMifkqWerrdIsLrbJMEaD/JRJFUSeFxaJVJx9uch2mhXMy+PJsIQ=@vger.kernel.org X-Gm-Message-State: AOJu0YyNM445q3YjiDQ+xtTFEGchrKKXShZZAncwmW8W8zyQttkFkQG3 vD4yj228IilUzHjofX9/3dsadeWCVbu6u3ITRIkT+v8XRw0xMqXXGgSFBECfZQls9wHb0pRppI3 IsskGlAohXJH/w9KSWrvSH929BWpMtf2C7+ZpbaFPEL0+7/v8i9UUKNIB0QNfztXRHDjs0Wlz8g == X-Gm-Gg: ASbGnctLIA5oecLq1N4wNYeN1+aHfnKbB0cA5HpRK3zv2a2IDDXZOGwLEEJHqns69Bp uYKkDnRzVsFToI8RCdiHjJY1SFVAAvFG1Rm1yKBIOBJd0KxP3AzJbADZFD7gL5tpHriFV2Z79ps 3tp9M3f0MZvz9zNla8H5c23kiIAZDLjWPlfjEhcRkLmVSVTc8mZ/X36fMOF6mwjWWyLGsrjpcTk vmsxcktNMD3H4RowxP2Xl6GpuU4jSALsNEFA2vaTM3XSh4iMZP6FbbWQeHw3PEYUiVMlkWm0hUx eKRVIDWe/2ZigUiUmTdKsev2yYGMlSZjT+dvHpHrukxFxWdqXnZRb/HKa9Tz1Ii129TcTlNVEY/ 5yFQ6TEH03khPJQCyfWxzBdXi+uqS5BbiCAdGIErNuJl7mZLAn4e9fBRXJS12JG4UsMA= X-Received: by 2002:a05:600c:3111:b0:45b:8c5e:5f8 with SMTP id 5b1f17b1804b1-45b8f43c876mr21537385e9.28.1756745212735; Mon, 01 Sep 2025 09:46:52 -0700 (PDT) X-Google-Smtp-Source: AGHT+IG+tnHEYgHg2xJrHLCrJvwVRM4CI/+qfgYSG+gAdqo4scSeNuoqAVtK5k8iywZ6wC6u9AF1Ug== X-Received: by 2002:a05:600c:3111:b0:45b:8c5e:5f8 with SMTP id 5b1f17b1804b1-45b8f43c876mr21536995e9.28.1756745212302; Mon, 01 Sep 2025 09:46:52 -0700 (PDT) Received: from ?IPV6:2003:d8:2f37:2b00:948c:dd9f:29c8:73f4? (p200300d82f372b00948cdd9f29c873f4.dip0.t-ipconnect.de. [2003:d8:2f37:2b00:948c:dd9f:29c8:73f4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b8f6cd502sm15397475e9.1.2025.09.01.09.46.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Sep 2025 09:46:51 -0700 (PDT) Message-ID: Date: Mon, 1 Sep 2025 18:46:44 +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: Baolin Wang , Dev Jain , Lorenzo Stoakes Cc: Nico Pache , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, ziy@nvidia.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> <2a141eef-46e2-46e1-9b0f-066ec537600d@linux.alibaba.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: <2a141eef-46e2-46e1-9b0f-066ec537600d@linux.alibaba.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: a9sv9LD7bjQplpp6RmgwNKJSpzzrS6G3n3Y5ARo5e54_1756745213 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 29.08.25 03:55, Baolin Wang wrote: > > > On 2025/8/28 18:48, Dev Jain wrote: >> >> On 28/08/25 3:16 pm, Baolin Wang wrote: >>> (Sorry for chiming in late) >>> >>> On 2025/8/22 22:10, David Hildenbrand wrote: >>>>>> 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". >>> >>> If we only allow setting 0 or 511, as Nico mentioned before, "At 511, >>> no mTHP collapses would ever occur anyway, unless you have 2MB >>> disabled and other mTHP sizes enabled. Technically, at 511, only the >>> highest enabled order would ever be collapsed." >> I didn't understand this statement. At 511, mTHP collapses will occur if >> khugepaged cannot get a PMD folio. Our goal is to collapse to the >> highest order folio. > > Yes, I’m not saying that it’s incorrect behavior when set to 511. What I > mean is, as in the example I gave below, users may only want to allow a > large order collapse when the number of present PTEs reaches half of the > large folio, in order to avoid RSS bloat. How do these users control allocation at fault time where this parameter is completely ignored? -- Cheers David / dhildenb