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 5BBEB3FA5F1 for ; Wed, 9 Sep 2026 09:36:34 +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=1788946598; cv=none; b=grPWRfpuz6mfrrQ4oTjPo6ifufey08bdzDC4717pLz7Qy6W1hYNzptdbBjqvmUFSWqACDHTM1XMHUKeIpuqBXCP1yCHpFig7v8kl9Iabaaf0nmbllIhlq89rIjEaZc3dc5G3rorTp1X1B3HWY5oSYuaCQrZ5+ClgMBEiw/Y8Y4k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788946598; c=relaxed/simple; bh=k96jBocCXsWl08XcAx17sazM8Mekg94Kav2EvPKH6YQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jRbhHUCw/uhhhuZm2iNNJrd8+m2YNE5DKk01WFjVtnu/nJx3XVXret9UWtcmDSq6F7j6eQZYg/xIKMQTd8TN1zWcGsY1Iti7wjgndWHgnQv0O84Q/AvYmWFnMLOlWi1wMwRA4oDeRzsLuRwug+l4LA2fgmNVBBwjv85ZV/EjCnw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Qb/l7rzW; 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="Qb/l7rzW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 518AF1F00A3A; Wed, 9 Sep 2026 09:36:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788946593; bh=61cn5W91VBgvdwAX5AGeN1SkiyX6gawVNp1MxJrLTEc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Qb/l7rzWJ5jbqv8kKCDnAS6EuQ3N4KRM9M6u68pQwe2chd8OrgoTZKKpb5eQ3HzPY erNvfk1LZ29flRIIMHMsdmRijv1d2gQ/CFcYqnFXcWFwmUqxwXAr00M5yPw+jENdHr mitXp+TI8vZtJbOyiHFndFgJzr8q5gJ/0+7g0kMOC9V033D9F7eVTUQfSmh31yFS7t Z3QLs6LyQWRUfP78dzT8o2Jg9a34VdGDp7iVITbIZMg53eWsLhCzJ70VTZ9FBfLxI4 /rPy6rxpcFijryXs3wqZ314cxXvJemCNFAcWmib7LWrO9UGG9bHDmdNzngJhp70/Cd EjUwamppEjhlw== Message-ID: Date: Wed, 9 Sep 2026 11:36:28 +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 v5 03/17] mm/mm_init: skip initializing shared vmemmap tail pages To: Muchun Song , Andrew Morton , Oscar Salvador Cc: Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Michal Hocko , David Laight , "Liam R . Howlett" , Suren Baghdasaryan , Qi Zheng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song References: <20260825084608.47437-1-songmuchun@bytedance.com> <20260825084608.47437-4-songmuchun@bytedance.com> 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: <20260825084608.47437-4-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/25/26 10:45, Muchun Song wrote: > memmap_init_range() initializes every struct page in the target range. > For compound pages with vmemmap optimization, the tail struct pages are > backed by a shared vmemmap page. > > Initializing those tail struct pages would overwrite the shared > vmemmap page contents, requiring users such as HugeTLB to restore the > metadata afterwards. > > Track the compound order for HVO-backed sections and use that metadata > to detect struct pages that fall into the shared tail vmemmap range. > Skip those shared tail pages in memmap_init_range(), then initialize > pageblock migratetypes for the processed range with a helper after the > per-page initialization loop. > > Keep direct mem_section access inside sparse helpers by exposing > pfn_to_section_order() to users that only need the order associated with > a PFN. This lets memmap_init_range() skip shared tail vmemmap pages > without exposing __pfn_to_section() to !SPARSEMEM builds. > > This is a preparatory change for consolidating handling across users of > vmemmap optimization, and it also avoids redundant initialization of > shared tail vmemmap pages during early boot. That early-boot benefit > appears only once HugeTLB is switched to this common handling, since > HugeTLB is the early-boot user that creates those shared tail vmemmap > pages. > > Signed-off-by: Muchun Song > --- > v5: > - Add comments for pageblock migratetype helper callers and shared > tail vmemmap skipping (suggested by Mike Rapoport) > > v4: > - Rename pfn_vmemmap_optimizable() to vmemmap_optimizable_pfn() > for consistency with vmemmap_optimizable_order() > > v3: > - Replace the !SPARSEMEM __pfn_to_section() stub with > pfn_to_section_order() (suggested by Mike Rapoport) > > v2: > - Fold section order tracking into the first user instead of keeping a > standalone API-only patch (suggested by Mike Rapoport) > - Rename page_vmemmap_optimizable() to pfn_vmemmap_optimizable() and > pass a PFN directly (suggested by Mike Rapoport) > - Initialize pageblock migratetypes from a helper after the per-page > loop (suggested by Mike Rapoport) > - Use a 1G PFN chunk for cond_resched() in the pageblock helper > (suggested by Mike Rapoport) > - Guard section_order() with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP so > it returns 0 when HVO is disabled and lets the compiler optimize the > code as much as possible (suggested by Mike Rapoport) > - Explain why the !SPARSEMEM __pfn_to_section() stub belongs here > (suggested by Mike Rapoport) > --- > include/linux/mmzone.h | 8 ++++++++ > mm/mm_init.c | 40 +++++++++++++++++++++++----------------- > mm/sparse.h | 33 +++++++++++++++++++++++++++++++++ > 3 files changed, 64 insertions(+), 17 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 5fb9b37819d5..df31cac12311 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -2022,6 +2022,14 @@ struct mem_section { > unsigned long section_mem_map; > > struct mem_section_usage *usage; > +#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP > + /* > + * Normally, sections hold regular (order-0) pages. However, for > + * sections with HVO enabled, this tracks the compound page order > + * to enable deduplication of redundant vmemmap pages. > + */ > + unsigned int order; order is a way too generic name for this. page_order? compound_page_order? -- Cheers, David