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 434624C6C for ; Tue, 17 Feb 2026 15:31:06 +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=1771342267; cv=none; b=aFUIt64I1ksbZg4Z7idGSirB1F5h6lwmEWnjz4Tx2JdjYnk/pedDXDMyDtNKPiG18TLumiiv+J2/RUBl5X8wCsIgNQ21xnOKySljzNRBJCZDLblM1rFoo+J4kB+nxD3ZdrPecgBISwqk8HjK5vCzk3pNr/a2lxqoN3ma4MMc6+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771342267; c=relaxed/simple; bh=fqSMcax7vtm4ZgUHabaHUWlF6/dmxm7Ucda8BEDwr9A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=daN5/7wTXmACVBv0rnzFu3qMQ4U0Vcu9wZpQyg/5ZuTu1w95BHrx9J7VjyL06YK8cqJjXHciLb3xr88iMNPJlB7e7aeVRFjUhgK1g4Y4QCzdK1182JTSlfBDu4PS8Ya/jIgEDxGFlwPKCaj8y6QeCT0Kp1HIOIPu+NKi9Qb7pGk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qoF2bGB4; 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="qoF2bGB4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7E7BFC4CEF7; Tue, 17 Feb 2026 15:31:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771342266; bh=fqSMcax7vtm4ZgUHabaHUWlF6/dmxm7Ucda8BEDwr9A=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=qoF2bGB4TOpQ2SGQahjnxSiiPTt3l/CjhfM3VcPrE9zfdUGNUHZ5MoONmP6xrsz/A HuS0th4xYMm8GGrVHYS04f+5fToBqo3UmpmZZIEhJBn5b3TO/3L0dkj0xcbO6HWCna Y4tXZ7vizt4Rpr4G7DLZTmVCZtTVrGWANdY0nRvOPJtTylE5LNup/jdvM5h9+Cl1IW zIPwkdu529QzsQ3sKTP+H69byLiMQiZddDetCvSQ2SBNzGQjgful6ZB0+LRhUFMqaC RJABvnyMSVPdmrl08JxW0mYEpMJQGcbXlgtAJiSSoytjlV9CTtvVzHmBr/b7rQFN5R FB6a/EZiXciLg== Message-ID: <2e68ef61-dcf2-46b2-913f-14980a104faf@kernel.org> Date: Tue, 17 Feb 2026 16:30:59 +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: [LSF/MM/BPF TOPIC] Per-process page size To: Matthew Wilcox , Dev Jain Cc: lsf-pc@lists.linux-foundation.org, ryan.roberts@arm.com, catalin.marinas@arm.com, will@kernel.org, ardb@kernel.org, hughd@google.com, baolin.wang@linux.alibaba.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260217145026.3880286-1-dev.jain@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/17/26 16:22, Matthew Wilcox wrote: > On Tue, Feb 17, 2026 at 08:20:26PM +0530, Dev Jain wrote: >> 2. Generic Linux MM enlightenment >> --------------------------------- >> We enlighten the Linux MM code to always hand out memory in the granularity > > Please don't use the term "enlighten". Tht's used to describe something > something or other with hypervisors. Come up with a new term or use one > that already exists. > >> File memory >> ----------- >> For a growing list of compliant file systems, large folios can already be >> stored in the page cache. There is even a mechanism, introduced to support >> filesystems with block sizes larger than the system page size, to set a >> hard-minimum size for folios on a per-address-space basis. This mechanism >> will be reused and extended to service the per-process page size requirements. >> >> One key reason that the 64K kernel currently consumes considerably more memory >> than the 4K kernel is that Linux systems often have lots of small >> configuration files which each require a page in the page cache. But these >> small files are (likely) only used by certain processes. So, we prefer to >> continue to cache those using a 4K page. >> Therefore, if a process with a larger page size maps a file whose pagecache >> contains smaller folios, we drop them and re-read the range with a folio >> order at least that of the process order. > > That's going to be messy. I don't have a good idea for solving this > problem, but the page cache really isn't set up to change minimum folio > order while the inode is in use. In a private conversation I also raised that some situations might make it impossible/hard to drop+re-read. One example I cam up with if a folio is simply long-term R/O pinned. But I am also not quite sure how mlock might interfere here. So yes, I think the page cache is likely the one of the most problematic/messy thing to handle. -- Cheers, David