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 049D4313E20 for ; Tue, 14 Oct 2025 12:59:36 +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=1760446778; cv=none; b=jnnaRtAROKBWq53yGNPcJjkHamhdFpue1Fz0pjdNWTGLapG4jycoR8gI/xUD+RGHQoKx6qmJyaIiKiBpyyArVEpaE7WBH+YDnKNhZDu7fJgEPzVJCfbCr7lW3f7qE9eogUOaVY4NX1wCksBZ8t5tX7u3Ggbn89tlsyNzalcCEQw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760446778; c=relaxed/simple; bh=Z1Th0V3A9t5q0RL6uoXSwWvKS3kowUSTZ0Ef18CL46Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=T5hwUK8cRW5xVygu1qNkmznbWqtNRjPG07k8e64hpMdRu+yUd2In4dqMgEG4GKUomN4yLRTRKPhrQksfNocnAUViNPoSsUcTE7t/EBN64a5upqOSv6do3MHS2C0GUl8D6tiIJ0q+y3MX1KwJe/QPdYfYvdqimsmes5U7mo9OPC0= 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=clN21IHz; 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="clN21IHz" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760446775; 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=iu1mp0L5rze+u9w9cyraP7Gulphe1rkUj/3PhF2TPeI=; b=clN21IHzDunTXGyH2xLvFYzkljs0b7mcnhSNftf6W3sW8WpdwD2L9Nu41pXm1yA7VVpu0D qYUPHlQrLFN4Q7B8FrUMv3tGTtXdtUOA70C0KJx0oCRjXVGxaR0JIFi/JISZ0q7xUiGRmE ewvqnfRPyoPlp56b5jBM12IqvhgytN4= Received: from mail-ej1-f70.google.com (mail-ej1-f70.google.com [209.85.218.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-442-dY7b_lWzM2aDCKW2CM-jVA-1; Tue, 14 Oct 2025 08:59:34 -0400 X-MC-Unique: dY7b_lWzM2aDCKW2CM-jVA-1 X-Mimecast-MFC-AGG-ID: dY7b_lWzM2aDCKW2CM-jVA_1760446773 Received: by mail-ej1-f70.google.com with SMTP id a640c23a62f3a-b3cbee9769fso698885766b.3 for ; Tue, 14 Oct 2025 05:59:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1760446773; x=1761051573; 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=iu1mp0L5rze+u9w9cyraP7Gulphe1rkUj/3PhF2TPeI=; b=g9IyzyOJ1GudQpOahnxaH2XOW6to4b+S19qPqC4Hj8Vl20B+VT2ivwkGz+LRkWrgQO D7QsYtes0z/7c+n2H4U1QHf8gwDOLDKqbGVNm4chHCEoZ0kY6asQIVSgVvoYwoh/ToWI smBSFo1cY4lWzTJGLHqBzO3D+c7BPoKjZVALZ2RUWmUXOaYEpeSAcZAXSZBoS1WLNUEP Ws5BGH+B/3RWChar9B/wzX/z4qOC83yL/skICc7EJ0XnV+edrSa/nwINN9YEyX0ICW5A RRK2/EggTr8l50WOCKFJIGC1+Jf9+KM9yHgMWG5qlrOrRHiZDT3I71a+HIW9+LOmkN09 GVmg== X-Forwarded-Encrypted: i=1; AJvYcCXc4p6Uc1HZDcI8ZwwyvFWDMjbOglpItxw9V7CN/2WGgAj2hxrNNGibQ88H7vrGBcK74QwvoOPb@vger.kernel.org X-Gm-Message-State: AOJu0YwZOEi2c7/I8uqlzu9pC7epYjx/b74wV+hGKYPLGGQVXycMGwQr bPCcQdtBEuGvlqR4Dm9k6BWGPvXVse3U59TxYNmmB/AjRF8xFugI3TLp6fT34to+I73kq9JgiUF PnLeQz/y8HFWyUzwO8Spdmb2ZFOT4UO4m/UOEfvHcvpA2hiRJM5GE/JM9Dwo= X-Gm-Gg: ASbGnct9FOvqOmXQBsoAoRL1D9hf6+Rrf3w4j3Jj4k4RcPAUHuCxo2ZWUmLoKQeFs8P lIqy3pRk59PpQT/3ppoGEyjrEeFfNggHOwkTbjosBZ6wp0jgKsF7p8XOcqUsjM2bbPpdPW7Ki4B fP1nXX7sYXoZdV7pqLQouIfVsMZ1MYe+wVJraC1mAvwKxTG+OHkv5T4pUc4OZx7FPsL721GW4xu RvT/MLa88hpCOeHKRWFPr+VTWTHPP3AX64tMG1aWT/tVR1c02f+FPkkSVUdVWp9Bw1tsl6KYqAz yoMU2NDrKgGZ2O0oIcDYrsIblJLu4sN4TtamLvVu3nhd0hZFCN85sglivmUGcLf832X1O7aHog= = X-Received: by 2002:a17:906:f5a5:b0:b29:c2ae:78f8 with SMTP id a640c23a62f3a-b50ac5d08bamr2706964166b.46.1760446773185; Tue, 14 Oct 2025 05:59:33 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEkEiy+cHw9UIH18Z36gnOBTWV4pz/7vpgUvMjb/aSdBKnsv8qXvi1i95BnCc/gOYElOXfN6Q== X-Received: by 2002:a17:906:f5a5:b0:b29:c2ae:78f8 with SMTP id a640c23a62f3a-b50ac5d08bamr2706957766b.46.1760446772515; Tue, 14 Oct 2025 05:59:32 -0700 (PDT) Received: from ?IPV6:2a09:80c0:192:0:5dac:bf3d:c41:c3e7? ([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b58244d17e1sm725071566b.75.2025.10.14.05.59.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Oct 2025 05:59:31 -0700 (PDT) Message-ID: <71380b43-c23c-42b5-8aab-f158bb37bc75@redhat.com> Date: Tue, 14 Oct 2025 14:59:30 +0200 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 20/20] mm: stop maintaining the per-page mapcount of large folios (CONFIG_NO_PAGE_MAPCOUNT) To: Wei Yang Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, Andrew Morton , "Matthew Wilcox (Oracle)" , Tejun Heo , Zefan Li , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn References: <20250303163014.1128035-1-david@redhat.com> <20250303163014.1128035-21-david@redhat.com> <20251014122335.dpyk5advbkioojnm@master> 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: <20251014122335.dpyk5advbkioojnm@master> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 14.10.25 14:23, Wei Yang wrote: > On Mon, Mar 03, 2025 at 05:30:13PM +0100, David Hildenbrand wrote: > [...] >> @@ -1678,6 +1726,22 @@ static __always_inline void __folio_remove_rmap(struct folio *folio, >> break; >> case RMAP_LEVEL_PMD: >> case RMAP_LEVEL_PUD: >> + if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) { >> + last = atomic_add_negative(-1, &folio->_entire_mapcount); >> + if (level == RMAP_LEVEL_PMD && last) >> + nr_pmdmapped = folio_large_nr_pages(folio); >> + nr = folio_dec_return_large_mapcount(folio, vma); >> + if (!nr) { >> + /* Now completely unmapped. */ >> + nr = folio_large_nr_pages(folio); >> + } else { >> + partially_mapped = last && >> + nr < folio_large_nr_pages(folio); > > Hi, David Hi! > > Do you think this is better to be? > > partially_mapped = last && nr < nr_pmdmapped; I see what you mean, it would be similar to the CONFIG_PAGE_MAPCOUNT case below. But probably it could then be partially_mapped = nr < nr_pmdmapped; because nr_pmdmapped is only set when "last = true". I'm not sure if there is a good reason to change it at this point though. Smells like a micro-optimization for PUD, which we probably shouldn't worry about. > > As commit 349994cf61e6 mentioned, we don't support partially mapped PUD-sized > folio yet. We do support partially mapped PUD-sized folios I think, but not anonymous PUD-sized folios. So consequently the partially_mapped variable will never really be used later on, because the folio_test_anon() will never hit in the PUD case. -- Cheers David / dhildenb