From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A80DC439323; Wed, 8 Jul 2026 15:13:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783523612; cv=none; b=rU4yT8CP/764caumC09ewWsZb7CTkuf13u1btXqPPdt3aJHfHDMC5MzZ0TNNu2Ym1khOmS/tePTdxlVOig2VgQhNIXfF6KZB7bMcrreriMO1spl7ZJ4eHOOlIia4GQKfi2wFdDiZ2VsrIsvmqSabr2fuyU5JZi6UZ6OehMmtfFQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783523612; c=relaxed/simple; bh=EAs1wLxgxUr8QphoNCTnwBt9V7QgesQjY4CSEp9rbJA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CZWjO2mnmHfJKdndRE4V3tfu6bUS4gQXk/ATA2xQvYyhrpSj/EZ2Fta+G5gX7/u5Kl1zFKs53lNxxKNtYJ1HVJ3tSwZe3YXhler6M13slfiq55WGpbu0Ou8VWCSumO9yHbKHPozGSdtP0D0Odux/Z+UFWcY0fIN2PTDoqVwnVpc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=b172Ftkd; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="b172Ftkd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E062A1F000E9; Wed, 8 Jul 2026 15:13:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783523610; bh=dY3UhUcYvYikZtGBYs+3zTBokdgjfjfU+WDdt96CQOU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=b172FtkdibBF/k8qkdVxwxVxIoxhk5PUXuLfSOQ7NIgWDpyJiB5oHp2Cwis1F1Acn mYkDzjL3ltm+oX1pUW4W7R9+SDSsMB0L3BPLtGEsHeXrhPXSyVKi/pXskqC7uwZfXR AlWQ3oFqrjN1RqIHOyB2xXwUrQ+z6f1FOJXVvv2+iWBhVti1ziuzWXnII0b2U/SVLi K07SFb5qMFexZYq8G31KTP2VkISk/Gl15rwNKkFIPURnzWsPpiZhuT+CYIrW3IsG+c msmTCOAoNIPeRx6zu14UEW7nMgVQ1eJnHAEi7px2+8RkVmtdCex1cSEYz9pCQ/+jkh 51O8uPaiOQxKA== Message-ID: Date: Wed, 8 Jul 2026 17:13:21 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/10] mm: provide free_reserved_pages(), removing x86 variant To: Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Muchun Song , Oscar Salvador Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org References: <20260708-bootmem_info_part2-v1-0-156ce4986598@kernel.org> <20260708-bootmem_info_part2-v1-2-156ce4986598@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20260708-bootmem_info_part2-v1-2-156ce4986598@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/8/26 16:10, David Hildenbrand (Arm) wrote: > Let's extend free_reserved_page() in page_alloc.c to free_reserved_pages(), > dropping the custom x86 variant. The common-code variant will consume an > order, so adjust the x86 callers accordingly. > > Make free_reserved_pages() assume that we are freeing ordinary > high-order pages, just with the special "reserved" flavor. The target > use case for now is freeing vmemmap PMD pages. > > Set the refcount directly to 0 (instead of 1) and call > __free_frozen_pages(). Add some kerneldoc. Use a single > adjust_managed_page_count() call. > > Signed-off-by: David Hildenbrand (Arm) > --- > arch/x86/mm/init_64.c | 8 +------- > include/linux/mm.h | 8 ++++++-- > mm/page_alloc.c | 33 ++++++++++++++++++++++++++------- > 3 files changed, 33 insertions(+), 16 deletions(-) > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index 69e36f02a663a..320e742b0bb3f 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -1000,12 +1000,6 @@ int arch_add_memory(int nid, u64 start, u64 size, > return add_pages(nid, start_pfn, nr_pages, params); > } > > -static void free_reserved_pages(struct page *page, unsigned long nr_pages) > -{ > - while (nr_pages--) > - free_reserved_page(page++); > -} > - > static void __meminit free_pagetable(struct page *page) > { > /* bootmem page has reserved flag */ > @@ -1038,7 +1032,7 @@ static void __meminit free_vmemmap_pages(struct page *page, unsigned int order, > while (nr_pages--) > put_page_bootmem(page++); > } else { > - free_reserved_pages(page, nr_pages); > + free_reserved_pages(page, order); > } > } else { > __free_pages(page, order); > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 113e1752548c2..62b261cccf16f 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3993,8 +3993,12 @@ extern unsigned long free_reserved_area(void *start, void *end, > > extern void adjust_managed_page_count(struct page *page, long count); > > -/* Free the reserved page into the buddy system, so it gets managed. */ > -void free_reserved_page(struct page *page); > +void free_reserved_pages(struct page *page, unsigned int order); > + > +static inline void free_reserved_page(struct page *page) > +{ > + free_reserved_pages(page, 0); > +} > > static inline void mark_page_reserved(struct page *page) > { > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a63733dac659e..9311d1f3793ad 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6381,15 +6381,34 @@ void adjust_managed_page_count(struct page *page, long count) > } > EXPORT_SYMBOL(adjust_managed_page_count); > > -void free_reserved_page(struct page *page) > +/** > + * free_reserved_pages - free reserved pages > + * @page: First page to free. > + * @order: The page order to free. > + * > + * Free pages allocated through memblock during boot, letting the buddy > + * manage them from now on. > + * > + * @page must be naturally aligned to the order and the order must not > + * exceed MAX_PAGE_ORDER. All pages must be reserved. > + */ > +void free_reserved_pages(struct page *page, unsigned int order) > { > - clear_page_tag_ref(page); > - ClearPageReserved(page); > - init_page_count(page); > - __free_page(page); > - adjust_managed_page_count(page, 1); > + const unsigned long nr_pages = 1UL << order; > + int i; > + > + VM_WARN_ON_ONCE(!IS_ALIGNED(page_to_pfn(page), nr_pages)); > + VM_WARN_ON_ONCE(order > MAX_PAGE_ORDER); > + > + for (i = 0; i < nr_pages; i++) { > + clear_page_tag_ref(page + i); > + ClearPageReserved(page + i); > + set_page_count(page + i, 0); Sashiko raises in reply to #4 that PFN walkers trying to grab pages could see their reference getting overridden. While that is not something we should be worrying about (or fixing in old code), I think it's best to ClearPageReserved() after set_page_count(), so someone actually trying to grab a reference would have the chance to rely on PageReserved from being a reliable indication. -- Cheers, David