From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 B55E22EA15E for ; Thu, 25 Sep 2025 09:43:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758793439; cv=none; b=a8bK1oxfm2FYGVDPiyvgIEiNpBesOG2Tqx6uydLLysQziayasvaRbMCB+IRRJcDa6N04vmWmSILnLdTfP1kN1Jaa4HGZWs2tpz0yMw02CIh8t0UKgUxJbTWQH/6NXDTeQ4nUlzJsQ+OvDfs0Xvr+m3totCShIiCZExeQK0ZwJ9c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758793439; c=relaxed/simple; bh=x/LZWRGmcf0e+J8ngIb3ZyGctnp639Z28hFh/h2k5nE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OcKadUcHFiQmC6YzmFrWykwlYUYjlI5c39d1myBYGyhNfAOZKL5mOj+ZWOuTF1OTa4PVtTo7b/HGnNq474cpZgEsicZ2HE2VHn+LZe78J8Mrm6d7VPnRRcvTji0R4bvc9GMYaFCYCr9m9OCwvq3TAEnlcFXICNzmgwocdSyhELc= 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=fpKB334C; arc=none smtp.client-ip=170.10.129.124 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="fpKB334C" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758793435; 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=6vydMaXs1eVl1UKvh2REpAhtxjKBRH6HzbTsqKiDoNg=; b=fpKB334CoCeNjcukJ8kF/HOXFUqbPt4n7uMSWbxJiGhcn9WgnJzHrrYJ7/U8KVVVxM7nj5 GoubmQwWSy/wVXCU9zU29xY8hGkmkrUKvzoQNG1W6Uo4il/+hc+YRLz3qNEUqqYDKOwF06 zrxsPZTrArAE3hnIkOAiXwV/6nTQwss= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-317-YZcaEMX9P0uURctinmWbuw-1; Thu, 25 Sep 2025 05:43:53 -0400 X-MC-Unique: YZcaEMX9P0uURctinmWbuw-1 X-Mimecast-MFC-AGG-ID: YZcaEMX9P0uURctinmWbuw_1758793432 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-46e36686ca1so3493835e9.2 for ; Thu, 25 Sep 2025 02:43:53 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758793432; x=1759398232; 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=6vydMaXs1eVl1UKvh2REpAhtxjKBRH6HzbTsqKiDoNg=; b=M0pf1DvhEGWACWTsg2uYMwpkIPdyfuvUgF98QruQI2DKQhYGluWDtu4UqxRKmKnA5m W2iQjSbiHZrwTz3UC6w9K/amM+vzEjOtT9lF9+Ed0sH9MhzghZipVuYGztQhu4uToZzA ybxcBBWoU93WesuP6inGfAN7qiv2F6C8D3b3WiEVt8yaxGzxGHUZIwf3WJAougncwqar 1dhXRcRFnEHHs4LvrQGI1EqAZi4At82Jd0yOxEQsvP3etXgyDeCgMj9UqjbJqUUcR7FU fLKqsEDEqhR2H866Emkr5Px6u7qhr/XvB5CCOYbdo5/hTONRTabSD7lz9o1YNBNqoMzl 52pA== X-Forwarded-Encrypted: i=1; AJvYcCWB75Lnf0MI7dq4FbJNN/7QVNLLMTQ4kKOL45HeU2qbjVLdvQZ9sCbGwQaCaLm2QBJS1qWU1w==@lists.linux.dev X-Gm-Message-State: AOJu0YwFXexnNrA6sHyeYXRHtsw6191fVs+ez1dm51ZNlIaTH9knZIO9 LGm23q3FitxqwDLXwg260zgW3bfnY4U3Sl07syhpwjUZLnSKLepwn7Ygitxc/jNywjO84B1+EUP S+ZxFoL/9/VS+XeXUqQE+0aBvOAyMosra9RC2RfoO4VQSftw1OBU2JvPL X-Gm-Gg: ASbGncuYfirWHpMyjFBxHqisLemS+hzWKzEsRUe7aWc4RS2VMyngXwJ4MA30bh4R4hw gE49/ldHkMzhs0lEeW4DwQ3QEw2qpykEZW2IM2OjlmRilsbmR1au2mOlkVJZgSSo9Pf3Lk3ZmOb Y6PVZn+59RxvcEA0jXZ4+fR/LwZemFXT5lPLlSTnoA7ZZB7Xbq7RVdRlChnVOHIpF7QicN7wvBi hWoXE03hNsmf97MMG/TlxdkFBvmTO/Pdiu3bcDm+TWjUIgSzp/62m1RGN9hoDAGGPem+EjIP8Br VPGwViTXpYjOY30rwvuzdsdRinLjtyVoeCISaf8TYXVOpS6i5tfF7QbEcCp5ihqiKmMbag7djx9 x2Q6zHA6PxXwB791HZBzrlb/Ydz7mSJSlOhaYf2hpherOuv4j+huz+509mYfkcpBNMwKk X-Received: by 2002:a05:600c:5296:b0:45f:2cd5:507c with SMTP id 5b1f17b1804b1-46e32a131admr24812705e9.36.1758793431924; Thu, 25 Sep 2025 02:43:51 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEWz4LdemSwADsOpu90+REN4fMccxBh2uGX6ZV9Mxd0bjbe/Oflr7dE6fLA/sZVqFh7dcnOWg== X-Received: by 2002:a05:600c:5296:b0:45f:2cd5:507c with SMTP id 5b1f17b1804b1-46e32a131admr24812405e9.36.1758793431361; Thu, 25 Sep 2025 02:43:51 -0700 (PDT) Received: from ?IPV6:2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08? (p200300d82f3ff800c1015c9f3bc93d08.dip0.t-ipconnect.de. [2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e33bf70dcsm26209145e9.23.2025.09.25.02.43.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 02:43:50 -0700 (PDT) Message-ID: <1b6741fe-20ed-4a47-8e9b-24bd199f23f4@redhat.com> Date: Thu, 25 Sep 2025 11:43:48 +0200 Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v6 01/15] mm/zone_device: support large zone device private folios To: Alistair Popple , Zi Yan Cc: Balbir Singh , linux-kernel@vger.kernel.org, linux-mm@kvack.org, damon@lists.linux.dev, dri-devel@lists.freedesktop.org, Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Oscar Salvador , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , =?UTF-8?Q?Mika_Penttil=C3=A4?= , Matthew Brost , Francois Dugast References: <20250916122128.2098535-1-balbirs@nvidia.com> <20250916122128.2098535-2-balbirs@nvidia.com> <882D81FA-DA40-4FF9-8192-166DBE1709AF@nvidia.com> <9c263334-c0f3-4af0-88a8-8ed19ef6b83d@redhat.com> <66A59A5C-B54E-484F-9EB8-E12F6BD1CD03@nvidia.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: HgIkymX0ZZSsc_Fg4p7MZVlR7M2o5_W0nRgYAUrNdYY_1758793432 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 25.09.25 01:58, Alistair Popple wrote: > On 2025-09-25 at 03:36 +1000, Zi Yan wrote... >> On 24 Sep 2025, at 6:55, David Hildenbrand wrote: >> >>> On 18.09.25 04:49, Zi Yan wrote: >>>> On 16 Sep 2025, at 8:21, Balbir Singh wrote: >>>> >>>>> Add routines to support allocation of large order zone device folios >>>>> and helper functions for zone device folios, to check if a folio is >>>>> device private and helpers for setting zone device data. >>>>> >>>>> When large folios are used, the existing page_free() callback in >>>>> pgmap is called when the folio is freed, this is true for both >>>>> PAGE_SIZE and higher order pages. >>>>> >>>>> Zone device private large folios do not support deferred split and >>>>> scan like normal THP folios. >>>>> >>>>> Signed-off-by: Balbir Singh >>>>> Cc: David Hildenbrand >>>>> Cc: Zi Yan >>>>> Cc: Joshua Hahn >>>>> Cc: Rakie Kim >>>>> Cc: Byungchul Park >>>>> Cc: Gregory Price >>>>> Cc: Ying Huang >>>>> Cc: Alistair Popple >>>>> Cc: Oscar Salvador >>>>> Cc: Lorenzo Stoakes >>>>> Cc: Baolin Wang >>>>> Cc: "Liam R. Howlett" >>>>> Cc: Nico Pache >>>>> Cc: Ryan Roberts >>>>> Cc: Dev Jain >>>>> Cc: Barry Song >>>>> Cc: Lyude Paul >>>>> Cc: Danilo Krummrich >>>>> Cc: David Airlie >>>>> Cc: Simona Vetter >>>>> Cc: Ralph Campbell >>>>> Cc: Mika Penttilä >>>>> Cc: Matthew Brost >>>>> Cc: Francois Dugast >>>>> --- >>>>> include/linux/memremap.h | 10 +++++++++- >>>>> mm/memremap.c | 34 +++++++++++++++++++++------------- >>>>> mm/rmap.c | 6 +++++- >>>>> 3 files changed, 35 insertions(+), 15 deletions(-) >>>>> >>>>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h >>>>> index e5951ba12a28..9c20327c2be5 100644 >>>>> --- a/include/linux/memremap.h >>>>> +++ b/include/linux/memremap.h >>>>> @@ -206,7 +206,7 @@ static inline bool is_fsdax_page(const struct page *page) >>>>> } >>>>> >>>>> #ifdef CONFIG_ZONE_DEVICE >>>>> -void zone_device_page_init(struct page *page); >>>>> +void zone_device_folio_init(struct folio *folio, unsigned int order); >>>>> void *memremap_pages(struct dev_pagemap *pgmap, int nid); >>>>> void memunmap_pages(struct dev_pagemap *pgmap); >>>>> void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap); >>>>> @@ -215,6 +215,14 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn); >>>>> bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn); >>>>> >>>>> unsigned long memremap_compat_align(void); >>>>> + >>>>> +static inline void zone_device_page_init(struct page *page) >>>>> +{ >>>>> + struct folio *folio = page_folio(page); >>>>> + >>>>> + zone_device_folio_init(folio, 0); >>>> >>>> I assume it is for legacy code, where only non-compound page exists? >>>> >>>> It seems that you assume @page is always order-0, but there is no check >>>> for it. Adding VM_WARN_ON_ONCE_FOLIO(folio_order(folio) != 0, folio) >>>> above it would be useful to detect misuse. >>>> >>>>> +} >>>>> + >>>>> #else >>>>> static inline void *devm_memremap_pages(struct device *dev, >>>>> struct dev_pagemap *pgmap) >>>>> diff --git a/mm/memremap.c b/mm/memremap.c >>>>> index 46cb1b0b6f72..a8481ebf94cc 100644 >>>>> --- a/mm/memremap.c >>>>> +++ b/mm/memremap.c >>>>> @@ -416,20 +416,19 @@ EXPORT_SYMBOL_GPL(get_dev_pagemap); >>>>> void free_zone_device_folio(struct folio *folio) >>>>> { >>>>> struct dev_pagemap *pgmap = folio->pgmap; >>>>> + unsigned long nr = folio_nr_pages(folio); >>>>> + int i; >>>>> >>>>> if (WARN_ON_ONCE(!pgmap)) >>>>> return; >>>>> >>>>> mem_cgroup_uncharge(folio); >>>>> >>>>> - /* >>>>> - * Note: we don't expect anonymous compound pages yet. Once supported >>>>> - * and we could PTE-map them similar to THP, we'd have to clear >>>>> - * PG_anon_exclusive on all tail pages. >>>>> - */ >>>>> if (folio_test_anon(folio)) { >>>>> - VM_BUG_ON_FOLIO(folio_test_large(folio), folio); >>>>> - __ClearPageAnonExclusive(folio_page(folio, 0)); >>>>> + for (i = 0; i < nr; i++) >>>>> + __ClearPageAnonExclusive(folio_page(folio, i)); >>>>> + } else { >>>>> + VM_WARN_ON_ONCE(folio_test_large(folio)); >>>>> } >>>>> >>>>> /* >>>>> @@ -456,8 +455,8 @@ void free_zone_device_folio(struct folio *folio) >>>>> case MEMORY_DEVICE_COHERENT: >>>>> if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->page_free)) >>>>> break; >>>>> - pgmap->ops->page_free(folio_page(folio, 0)); >>>>> - put_dev_pagemap(pgmap); >>>>> + pgmap->ops->page_free(&folio->page); >>>>> + percpu_ref_put_many(&folio->pgmap->ref, nr); >>>>> break; >>>>> >>>>> case MEMORY_DEVICE_GENERIC: >>>>> @@ -480,14 +479,23 @@ void free_zone_device_folio(struct folio *folio) >>>>> } >>>>> } >>>>> >>>>> -void zone_device_page_init(struct page *page) >>>>> +void zone_device_folio_init(struct folio *folio, unsigned int order) >>>>> { >>>>> + struct page *page = folio_page(folio, 0); >>>> >>>> It is strange to see a folio is converted back to page in >>>> a function called zone_device_folio_init(). >>>> >>>>> + >>>>> + VM_WARN_ON_ONCE(order > MAX_ORDER_NR_PAGES); >>>>> + >>>>> /* >>>>> * Drivers shouldn't be allocating pages after calling >>>>> * memunmap_pages(). >>>>> */ >>>>> - WARN_ON_ONCE(!percpu_ref_tryget_live(&page_pgmap(page)->ref)); >>>>> - set_page_count(page, 1); >>>>> + WARN_ON_ONCE(!percpu_ref_tryget_many(&page_pgmap(page)->ref, 1 << order)); >>>>> + folio_set_count(folio, 1); >>>>> lock_page(page); >>>>> + >>>>> + if (order > 1) { >>>>> + prep_compound_page(page, order); >>>>> + folio_set_large_rmappable(folio); >>>>> + } >>>> >>>> OK, so basically, @folio is not a compound page yet when zone_device_folio_init() >>>> is called. >>>> >>>> I feel that your zone_device_page_init() and zone_device_folio_init() >>>> implementations are inverse. They should follow the same pattern >>>> as __alloc_pages_noprof() and __folio_alloc_noprof(), where >>>> zone_device_page_init() does the actual initialization and >>>> zone_device_folio_init() just convert a page to folio. >>>> >>>> Something like: >>>> >>>> void zone_device_page_init(struct page *page, unsigned int order) >>>> { >>>> VM_WARN_ON_ONCE(order > MAX_ORDER_NR_PAGES); >>>> >>>> /* >>>> * Drivers shouldn't be allocating pages after calling >>>> * memunmap_pages(). >>>> */ >>>> >>>> WARN_ON_ONCE(!percpu_ref_tryget_many(&page_pgmap(page)->ref, 1 << order)); >>>> >>>> /* >>>> * anonymous folio does not support order-1, high order file-backed folio >>>> * is not supported at all. >>>> */ >>>> VM_WARN_ON_ONCE(order == 1); >>>> >>>> if (order > 1) >>>> prep_compound_page(page, order); >>>> >>>> /* page has to be compound head here */ >>>> set_page_count(page, 1); >>>> lock_page(page); >>>> } >>>> >>>> void zone_device_folio_init(struct folio *folio, unsigned int order) >>>> { >>>> struct page *page = folio_page(folio, 0); >>>> >>>> zone_device_page_init(page, order); >>>> page_rmappable_folio(page); >>>> } >>>> >>>> Or >>>> >>>> struct folio *zone_device_folio_init(struct page *page, unsigned int order) >>>> { >>>> zone_device_page_init(page, order); >>>> return page_rmappable_folio(page); >>>> } >>> >>> I think the problem is that it will all be weird once we dynamically allocate "struct folio". >>> >>> I have not yet a clear understanding on how that would really work. >>> >>> For example, should it be pgmap->ops->page_folio() ? >>> >>> Who allocates the folio? Do we allocate all order-0 folios initially, to then merge them when constructing large folios? How do we manage the "struct folio" during such merging splitting? >> >> Right. Either we would waste memory by simply concatenating all “struct folio” >> and putting paddings at the end, or we would free tail “struct folio” first, >> then allocate tail “struct page”. Both are painful and do not match core mm’s >> memdesc pattern, where “struct folio” is allocated when caller is asking >> for a folio. If “struct folio” is always allocated, there is no difference >> between “struct folio” and “struct page”. > > As mentioned in my other reply I need to investigate this some more, but I > don't think we _need_ to always allocate folios (or pages for that matter). > The ZONE_DEVICE code just uses folios/pages for interacting with the core mm, > not for managing the device memory itself, so we should be able to make it more > closely match the memdesc pattern. It's just I'm still a bit unsure what that > pattern will actually look like. I think one reason might be that in contrast to ordinary pages, zone-device memory is only ever used to be used for folios, right? Would there be a user that just allocates pages and not wants a folio associated with it? It's a good question of that would look like when we have dynamically allocated struct folio ... > >>> >>> With that in mind, I don't really know what the proper interface should be today. >>> >>> >>> zone_device_folio_init(struct page *page, unsigned int order) >>> >>> looks cleaner, agreed. > > Agreed. > >>>> >>>> >>>> Then, it comes to free_zone_device_folio() above, >>>> I feel that pgmap->ops->page_free() should take an additional order >>>> parameter to free a compound page like free_frozen_pages(). > > Where would the order parameter come from? Presumably > folio_order(compound_head(page)) in which case shouldn't the op actually just be > pgmap->ops->folio_free()? Yeah, that's also what I thought. -- Cheers David / dhildenb