From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CFE823D6CC6; Wed, 18 Mar 2026 12:41:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773837680; cv=none; b=UUeMlWk/Z9darYKLGbaktZPnAcx9H8lcExJisayhTWpxkd95eLlTcvioeTEj/ZQhf4DRsGAKOY7rik3fkkRnoiXyaoE8y18Sepw7FxTl6dW9YyNI4XBFLXrLM/85c0jDgP9DkgMTGostth7B9Nnsr0ayIIvVU+XNcSo298pr8X4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773837680; c=relaxed/simple; bh=3cVeNY+pQvT7y9XfiCK6KuJy6FGGhon85ayumpItLTU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=L4TvFFtVPZA96x2MZsGmS2G7BIy2kGP5z2AQuL1XTeHGlCIwpwjXkpgcvMeki/2fvoDZEvXn4aOiwRsHKcN0hfNAI96Ch6yH2jfYycRnV2z2W3lBmRFavfq1FPOrvUTnX9JXaHUekYj/h3WH8cOeEr1W0k1CgbbWOlMCJenE2Eg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OYbuI4Mi; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OYbuI4Mi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 16E1CC19421; Wed, 18 Mar 2026 12:41:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773837680; bh=3cVeNY+pQvT7y9XfiCK6KuJy6FGGhon85ayumpItLTU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OYbuI4Mi7c5qsUy/G/ZYGrvOHFCTW/szfFBZDvDH5aP8kIIRGZbUSLe3/qhHSrc/Y 41rmRqo4gXjwtcd2pIfDtDknzJR/xDeA+GOJXyeDS1IBuazpueGcf+FqLyyKCVAiGH FA6ikYq18iYHNxP26mEdGY87syEk0AhR9k3CgUR/3F7Njsz+gc+bdyfihYE2u5XssX vgV7L7EjIhROfN0YidaQoPfiknxjUtXy9WkAZUlfT9zyCwW254gDon8u0nSJV4vCLz b2Um5Mc5dec1zf/Povf0u+Gh4REpE7RGbho1tXzu40Rz4eU5kxTb8mNQnrx8/CruWb 24sGJW49WJBXQ== Message-ID: Date: Wed, 18 Mar 2026 13:41:11 +0100 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 0/4] arm64/mm: contpte-sized exec folios for 16K and 64K pages To: Usama Arif , Andrew Morton , ryan.roberts@arm.com Cc: ajd@linux.ibm.com, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, brauner@kernel.org, catalin.marinas@arm.com, dev.jain@arm.com, jack@suse.cz, kees@kernel.org, kevin.brodsky@arm.com, lance.yang@linux.dev, Liam.Howlett@oracle.com, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, npache@redhat.com, rmclure@linux.ibm.com, Al Viro , will@kernel.org, willy@infradead.org, ziy@nvidia.com, hannes@cmpxchg.org, kas@kernel.org, shakeel.butt@linux.dev, kernel-team@meta.com, WANG Rui References: <20260310145406.3073394-1-usama.arif@linux.dev> <608c87ce-10d9-4012-b6e9-298d5a356801@kernel.org> <9e9edebb-3953-4bcd-80e2-614dcec5b402@linux.dev> <562fb349-c2d2-4fbe-83f9-75c26cc4b7ae@linux.dev> 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: <562fb349-c2d2-4fbe-83f9-75c26cc4b7ae@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/18/26 11:41, Usama Arif wrote: > > > On 16/03/2026 19:06, David Hildenbrand (Arm) wrote: >> On 3/13/26 20:59, Usama Arif wrote: >>> >>> >>> >>> So I see 2 benefits from this. Page fault and iTLB coverage. IMHO page >>> faults are not that big of a deal? If the text section is hot, it wont >>> get flushed after faulting in. So the real benefit comes from improved >>> iTLB coverage. >>> >>> For a 128M mapping, 2M alignment gives 64 contpte entries. Aligning >>> to something larger (say 128M) wouldn't give any additional TLB >>> coalescing, each 2M-aligned region independently qualifies for contpte. >>> >>> Mappings smaller than 2M can't benefit from contpte regardless of >>> alignment, so falling back to PAGE_SIZE would be the optimal behaviour. >>> Adding intermediate sizes (e.g. 512K, 128K) wouldn't map to any >>> hardware boundary and adds complexity without TLB benefit? >> >> I might be wrong, but I think you are mixing two things here: >> >> (1) "Minimum" folio size (exec_folio_order()) >> >> (2) VMA alignment. >> >> >> (2) should certainly be as large as (1), but assume we can get a 2M >> folio on arm64 4k, why shouldn't we align it to 2M if the region is >> reasonably sized, and use a PMD? >> >> > > So this series is tackling both (1) and (2). When I started making changes > to the code, what I wanted was 2M folios at fault with 64K base page size > to reduce iTLB misses. This is what patch 1 (and 2) will achieve. > > Yes, completely agree, (2) should be as large as (1). I didn't think about > PMD size on 4K which you pointed out. do_sync_mmap_readahead can give > that with force_thp_readahead, so this should be supported. In particular, imagine if hw starts optimizing transparently on other granularity, then the "smallest granularity" (exec_folio_order()) decision will soon be wrong. > > But we shouldn't align to PMD size for all base page sizes. As Rui pointed > out, increasing alignment size reduces ASLR entropy [1]. Should we max alignement > to 2M? That's why I said that likely, as an input, we'd want to use the mapping size or other heuristics. We wouldn't want to align a 4k mapping to either 64k or 2M. Long story short: the change in thp_get_unmapped_area_vmflags() needs some thought IMHO. -- Cheers, David