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 F0DC639F178; Thu, 19 Mar 2026 07:35:38 +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=1773905739; cv=none; b=JRJ+24wvXM0wRN9mx3qyhHw4WkLdOw4cQEmEl4FBaYqHEZDMlV7TD2t579XgPY0YsRQDkFIv8U6M2HOZrk2Lp1gARE7X9juFwiAijAH/APnHLFh+rAK2w0BKCoABYM4si4CBiO0M7SYlDQv4vq1gqOJ/ReiZyqJI2ebcJ7RfIhY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773905739; c=relaxed/simple; bh=uOcmZzh8d0O0DH5CbztsLp28CPyWd3JOtYbCAi4uwVo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qNg6mlm/+yV2n+NHHT/m4uldYBPWW+DW2wG49dzpWqrWcYzU2NgeACM4umMYXQlAlT6lwDVmBFF8P4DhqU7fJ7i+I2br6s+48V96dGU+7VHVXH8plP29gbiZD+Aq0SkCXF1FQloiG6F5L65wWbiK2A1SCKutpeKAyKxWqXwwFQ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=M8Zx0AuJ; 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="M8Zx0AuJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2405EC19424; Thu, 19 Mar 2026 07:35:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773905738; bh=uOcmZzh8d0O0DH5CbztsLp28CPyWd3JOtYbCAi4uwVo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=M8Zx0AuJEuSPkF07I/Ib4o3GDx/OLKcdDOkXqcU3T5+YDru7awKHBAqruc4v19NBh StSU8ZRucJPgwNH8201LF0ej6+1EMiJCIXBoEXMJf8a6TfGzE/bP8WQp1JHd8ZUAla qwYYfHpAfH/3vdfi0eIJt+O942Vv75P+thTYrqRSZ6L91LYZz6mHODG1A2ccSWgEYY bqL1Iui6q718lMcZmN7DmkKE7LQ1DYM4IiCXQm24u4Fy+HNwLFoseaAULcYVaiq8dq AViedRoS1YAVrRPNKDoQWeYzJ7ckZJNJwTjnWAX1cpdGwr/cgWENs/A/ENjyYgFEWo SD20UDN3q8nZw== Message-ID: Date: Thu, 19 Mar 2026 08:35:30 +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 1/4] arm64: request contpte-sized folios for exec memory 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 References: <20260310145406.3073394-1-usama.arif@linux.dev> <20260310145406.3073394-2-usama.arif@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/10/26 15:51, Usama Arif wrote: > exec_folio_order() was introduced [1] to request readahead of executable > file-backed pages at an arch-preferred folio order, so that the hardware > can coalesce contiguous PTEs into fewer iTLB entries (contpte). > > The current implementation uses ilog2(SZ_64K >> PAGE_SHIFT), which > requests 64K folios. This is optimal for 4K base pages (where CONT_PTES > = 16, contpte size = 64K), but suboptimal for 16K and 64K base pages: > > Page size | Before (order) | After (order) | contpte > ----------|----------------|---------------|-------- > 4K | 4 (64K) | 4 (64K) | Yes (unchanged) > 16K | 2 (64K) | 7 (2M) | Yes (new) > 64K | 0 (64K) | 5 (2M) | Yes (new) > > For 16K pages, CONT_PTES = 128 and the contpte size is 2M (order 7). > For 64K pages, CONT_PTES = 32 and the contpte size is 2M (order 5). > > Use ilog2(CONT_PTES) instead, which directly evaluates to contpte-aligned > order for all page sizes. > > The worst-case waste is bounded to one folio (up to 2MB - 64KB) > at the end of the file, since page_cache_ra_order() reduces the folio > order near EOF to avoid allocating past i_size. So, if you have a smallish text segment in a larger file, we'd always try to allocate 2M on 16k/64k? That feels wrong. Asking the other way around: why not also use 2M on a 4k system and end up with a PMD? And no, I don't think we should default to that, just emphasizing my point that *maybe* we really want to consider mapping (vma) size as well. -- Cheers, David