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 D3E352F28FC for ; Mon, 15 Sep 2025 08:51:53 +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=1757926315; cv=none; b=R1FRKChhu5vG+DTj/CLa5fuiYii8X44pO9BvcLKk51hccEsw/TBUbj5KRhsCN3I9xjQcV8/1dhkWwPuHe9Sq1s0TtSdpvo3ZCit/9pgOlrGtht/Z9w5buApDMfLwKJumjykGTfl7JlbH5NNA3ATHpjNgLRpLmL5wgZRQoK8ATDw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757926315; c=relaxed/simple; bh=K9DnZbwwc+Qgw1EQWLXUQAXITJLMxq0U4dFMNLyDULU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=nlOch5a7TxAoXKHKmV+eiJxrqyOxin9jKLsUTuGyH1EGXTajuG0t7KsWM/HX102nZIzdjsBRLteGC3zrnwqBbVvs4sEum1jvTVFFwRFB0wAh9/sspWUQ3pQjiP/HaXtx2sKcJoLus3cqO1P7Srm982pqmkVdiU9rX3INXStAFik= 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=BS103I9D; 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="BS103I9D" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1757926312; 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=LbC9+HlZ3wYD+Tu6w1/ck3ndJOKoJRqAyUbt5dHckC0=; b=BS103I9Do1L0NOrk6dUqyu74hxs2cc2O227FEF0hFkgdXe3FqBgm8xTFZ/6ChaDjqMrYWm ovCSQJm/NiskersB6Hc9ydNSm26G7UvOZ/4qsdFgdIEeTw8njv49P8KOnnaN6DIT1Ei+yw Z9Wr4tuJqi4tS4AgSe9b/a3rWPbBpTY= 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-380-fkRNgqKIP1aSUouMPozx0Q-1; Mon, 15 Sep 2025 04:51:51 -0400 X-MC-Unique: fkRNgqKIP1aSUouMPozx0Q-1 X-Mimecast-MFC-AGG-ID: fkRNgqKIP1aSUouMPozx0Q_1757926310 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-45b98de0e34so30947425e9.0 for ; Mon, 15 Sep 2025 01:51:51 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757926310; x=1758531110; 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=LbC9+HlZ3wYD+Tu6w1/ck3ndJOKoJRqAyUbt5dHckC0=; b=f51E8ABubDmB0QliClI3LsDh6YT8cHf61qn5ZETGb/ogkH0lgzRxMKfTdQFKMU0K4x +5vRNI3RJUACwSTGXZjFRapkVYneHEUm5hSQhvofO6RkhM7/FFo57HxI0637JOo2sOPb uMwMgstw+xpQJ7QUG4rlpq3aaGLqM9CnL6gMsto7jKL2nVnaaXYSjurlVl1u4HPgkywB WUAiw+4MK9YsVfAlVKSUiBxvtI4n8peHbwpuQ+QM/K/TX8dCx9+3Ss6kveEhdUovnGyY V0GW5RPBg4cL/4eMVowy/JRVjXevHf9I8/kD6XWCkig0PRa1ComqmmFNecmFq4BbVNbI E4Lg== X-Forwarded-Encrypted: i=1; AJvYcCU1vQxbW3FyM534FmgqdeFt7zh6W1LWSTxrYG+LfIW+unZiBjgKfdrUbrfZwYbXuiqQX4IqgzN1X7IKL2M=@vger.kernel.org X-Gm-Message-State: AOJu0Yz7BIpCCTIGpoRQDdES2nXq0Kn9YQmWoH68tbvbKFUuEYISgN/x MytM4ES1Q4koAl8U3igBhkWvgUA8azkVs6B3+tvagxp5RadFTiLwD9YeQoHnVQ1gFrLivQ+x6aC LzE8oqN1mKv1qNKAmVCqieJhj7Xu38WhngQJMf0aG9+4EXT9uwU+JS4Igw4tpa7cnzw== X-Gm-Gg: ASbGncveJ0oRN7hztuE8twwpOYN8/e+BUnOD5LLWnnd5tIUp7vdUQjV7BId5nWmu8oH 7aZCev34BRjHtTJ3nhXmSatArJan2H0/qFmIvoJvGkCJX8h+pkmfrlLAQImXlmEA1c+Nt3GSsj+ okIMQgudMT/hzz5D80sc6HSlRRCDXbB4YvtTrV8QLXMC2GSbhcA2NJQZQs8nZJWydW40CmhAJVC E5cq8FpPYF4v9DWBqXFgsbc/bpgiGA3qHhhuVVontFLoWix8UMc4IIwuOC1JTOtyGEDvuIeJMpD YRufi2L5Pd2DQjY9jGDt1u3cuwko7DTLE2jvTnCOp/iIKLOVtBGRpsBel0NWSRhyoWCR97lUpkl 0u7JN4LP3OhVzbaJK97gjWCdLA/MaFyqsfVKva+qWvR/XenN7t3gV0e1eKvPOVxLQ+90= X-Received: by 2002:a05:600c:6288:b0:45d:d1b0:5fa2 with SMTP id 5b1f17b1804b1-45f211f9fb6mr91702945e9.19.1757926310274; Mon, 15 Sep 2025 01:51:50 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHmehtCyxOr2v1ulJFD/llco5pkU8tfM63kgUUYxmqAqnpUwXE75+yd18OdpEGn1aaibMJcKg== X-Received: by 2002:a05:600c:6288:b0:45d:d1b0:5fa2 with SMTP id 5b1f17b1804b1-45f211f9fb6mr91702725e9.19.1757926309820; Mon, 15 Sep 2025 01:51:49 -0700 (PDT) Received: from ?IPV6:2003:d8:2f18:f900:e0ae:65d5:8bf8:8cfd? (p200300d82f18f900e0ae65d58bf88cfd.dip0.t-ipconnect.de. [2003:d8:2f18:f900:e0ae:65d5:8bf8:8cfd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45f2ff61f2bsm6962095e9.12.2025.09.15.01.51.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Sep 2025 01:51:49 -0700 (PDT) Message-ID: Date: Mon, 15 Sep 2025 10:51:48 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/huge_memory: fix shrinking of all-zero THPs with max_ptes_none default To: Dev Jain , Usama Arif , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Barry Song References: <20250905141137.3529867-1-david@redhat.com> <06874db5-80f2-41a0-98f1-35177f758670@gmail.com> <20e7f812-c1e7-455f-a523-08fc99024adb@arm.com> From: David Hildenbrand Content-Language: en-US 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: <20e7f812-c1e7-455f-a523-08fc99024adb@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 14.09.25 16:04, Dev Jain wrote: >>> --- >>> mm/huge_memory.c | 3 --- >>> 1 file changed, 3 deletions(-) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 26cedfcd74189..aa3ed7a86435b 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -4110,9 +4110,6 @@ static bool thp_underused(struct folio *folio) >>> void *kaddr; >>> int i; >>> >>> - if (khugepaged_max_ptes_none == HPAGE_PMD_NR - 1) >>> - return false; >>> - >> I do agree with your usecase, but I am really worried about the amount of >> work and cpu time the THP shrinker will consume when max_ptes_none is 511 >> (I dont have any numbers to back up my worry :)), and its less likely that >> we will have these completely zeroed out THPs (again no numbers to back up >> this statement). We have the huge_zero_folio as well which is installed on read. > FWIW, I am still hesitant on this patch because I think the whole deferred split lists + interaction with the shrinker should be cleaned up along this patch. > How about just doing a memcmp() between huge_zero_folio and folio? We know > exactly how this folio looks like, in case of max_ptes_none == 511, if it > is to be eligible for shrinking. I wouldn't really want to optimize for this case, especially given that (a) I want to remove all direct dependencies on max_ptes_none and any special values. (b) The huge zero folio is not always around (c) The kmap local prevents us from doing that (in particular on 32bit). -- Cheers David / dhildenb