From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7A7A8C5AD05 for ; Fri, 20 Feb 2026 16:50:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=OhJz6AO2smTz4OPHnhTTcMcb/SkGEP42mmzEHHMk7X8=; b=mmW27wcr2qNH1XRdQVT7OLwyyh VqNdb5L64rJa4t8K+lFyJv5f1DvzIp2TLN87m37q3Xu+DpvcywV40I3H6P6K/Lk0miKhnzWZCFSV3 m+F7MV/G1rVhilLkjjQ2BjIps+LlDloFtst63SRrje/MshQDimLPh6gF1UzSUubcBF47PjgvbAyWL 25nodcZV08zoDKVGvHN7MV0CGtG3AVmS4R7JM+Ko4tSu54cwVNQMIv30Zbke8Qp7+f+KM6VMiNcbV KywIAysYpF3Eqw/mfGTqFtwR4cQw+FsHFSwQPR9FWhcJWfXoHxzdzYSEDM+t4hQmGac4f6PBPhOTk TAQ71Cdg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vtTiP-0000000FKQc-0lUh; Fri, 20 Feb 2026 16:50:53 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vtTiN-0000000FKQ3-1PgS for linux-arm-kernel@lists.infradead.org; Fri, 20 Feb 2026 16:50:52 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id B34BC41AF2; Fri, 20 Feb 2026 16:50:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35BC8C116C6; Fri, 20 Feb 2026 16:50:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771606250; bh=+Uij/0xoD2fksuZzZkZLFNcIAKJYICDzDr0TGD6sxow=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=d5W1HDLzSBMx3frw2niVk0GR2O9vcnpmuDh3nVZ09DxzHczZ5uzY2u225TKsjUTua bZnCGRvMT7WmR5K5UJUVsUJk/Rt1oUCOQozAkKZYIbZ5sd1vuDPYRD+oXzRT//KPRH DvrTY8DWFMcDHceh3SgIZQCVBHw+KKQ9PO9czG3ta2WIyETUS5IG2NxNpHIC333463 3fjyC5hLQVzbEqVqV9OP0tgNsDBH5aj4jjeUmOX8aBQDVWuDn+VTfFHZSlo2clBzd6 ViGv4WtWdnCqQdApp6geo/GRYIvEtQRzpZfwufEoU/00iPUg7GvvN2ngvmfIGhopfE ecrZkicAFaTMA== Message-ID: <5f61a5fd-ab38-4635-aab8-5de515c4015a@kernel.org> Date: Fri, 20 Feb 2026 17:50:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] Per-process page size To: Matthew Wilcox Cc: Dev Jain , 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> <2e68ef61-dcf2-46b2-913f-14980a104faf@kernel.org> 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260220_085051_421259_C6921DAB X-CRM114-Status: GOOD ( 18.20 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2/20/26 05:49, Matthew Wilcox wrote: > On Tue, Feb 17, 2026 at 04:30:59PM +0100, David Hildenbrand (Arm) wrote: >> 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. > > So what if we convert to max-supported-order the first time somebody > calls mmap on a given file? Most files are never mmaped, so it won't > affect them. Yes! > And files that are mmaped are generally not written to. Well, let's say many mmaped files are not written to. :) > So there should not be much in the page cache for the common case. You'd assume many files to either get mmaped or read/written, yes. > And if no pages from the file have been mmaped yet, they cannot be pinned > or mlocked. Is there some other way for someone to block a page from getting evicted from the pagecache? We have this memfd_pin_folios() thing, but I don't think we have something comparable for ordinary pagecache files. ... putting them into a pipe and never reading from the pipe maybe (I assume that's what splice() does, but not sure if it actually places the pages in there or whether it creates a copy first)? But yes, doing the conversion on first mmap() should handle mlock+gup. -- Cheers, David