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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 510DFC77B7C for ; Sun, 7 May 2023 23:20:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 86F1F6B0078; Sun, 7 May 2023 19:20:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 81F836B007D; Sun, 7 May 2023 19:20:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 70E186B007E; Sun, 7 May 2023 19:20:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 5F3436B0078 for ; Sun, 7 May 2023 19:20:51 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id EFAAE14023C for ; Sun, 7 May 2023 23:20:50 +0000 (UTC) X-FDA: 80765031060.01.85D5A6E Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf09.hostedemail.com (Postfix) with ESMTP id 1BD9F140004 for ; Sun, 7 May 2023 23:20:46 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="HSDc7/Kb"; spf=none (imf09.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1683501648; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding:in-reply-to: references:dkim-signature; bh=Th+cg1WdpxBjx+qFGjiozltRGL4jA5g/nbgL8pl9X58=; b=3seUVhsS530/kxjUSF3hUHgHPuOCDupKaJ8i89XqFqBcVKCyfJc+qnI2S217AkIGrRRen8 rBnTsHwgaeCHyvAYqrvMip/0WQT2o+1wl6aY7iA1TMbaw3zdr2V5yXg2TztByx3lPm4vJ1 tFM6VsjEJ7n/wq9FEMgp+cSUfsqu1gI= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1683501648; a=rsa-sha256; cv=none; b=Iw/A0nSRT/te9PJa8sxV6Zd8zrOczrfeKgsAPfZHJcFLOGZjUjfSCSgEUPnaMrhlmz8XTi SPN5Wx5mODlj2Oc67kTTV02B693UOmLiZzWqUMF4PmXKdLt73aaQZaFpesL6kwFeja9YXM ahtFE2+4XK8p7u7B9CmPY0t4SGYprqg= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="HSDc7/Kb"; spf=none (imf09.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=Th+cg1WdpxBjx+qFGjiozltRGL4jA5g/nbgL8pl9X58=; b=HSDc7/KbLBzgDwKMe/Nc82Ijd2 P9PqS3fT7bgi5bvaLtQ/g0fOazuttTw3Q2/3bhq3oY9YPr8lLzhY7f/BHmpdzWePA5DB0scP9v5yS QZoHdGIkzzy6mTUk9Ig3DvUTYWC+2yJ3cBs058nFzgvQrhbU9FS8oQCgDcLjTWYiIAINVQWGqKqV/ Ve3oJOl6gYGuhaojFej6JvcZAajNBxG/3l5VJzifphaVrglZ9E/t6zk6P+MkRbRr2aAUQNK58Yj3+ nS12xEEyo19pgUMlA8F0yPgTDJSoeFFQeyPf44EfrDBy2PkPZo1UTfjULScBp+ET0mMD3ySZaib1V AYnkzgoA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pvngI-00DcxA-4I; Sun, 07 May 2023 23:20:42 +0000 Date: Mon, 8 May 2023 00:20:42 +0100 From: Matthew Wilcox To: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org Subject: [LSF/MM/BPF] Whither Highmem? Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1BD9F140004 X-Stat-Signature: mx45se3sq7i8wfr5ty7fmiaq3w3qjpwo X-Rspam-User: X-HE-Tag: 1683501646-696678 X-HE-Meta: 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 qojawp7j lr5r+6fmdHI7udw+oyohBIUcmyTcX4DKYudBNRTLfZGQYGzKQj/fLmTLvKsyHWo8SWUsTzv214XRhoDDZBhY3HB53EszU6mvBqDBIxinese8wb8WixyrOfpzzoXeXy1CC2MWssMe7BVUWQmAgcVgePOQDIbNJED18SA490FiYKXvAG7u2y9mEW8ETmQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000234, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: I see there's a couple of spots on the schedule open, so here's something fun we could talk about. Highmem was originally introduced to support PAE36 (up to 64GB) on x86 in the late 90s. It's since been used to support a similar extension on ARM (maybe other 32-bit architectures?) Things have changed a bit since then. There aren't a lot of systems left which have more than 4GB of memory _and_ are incapable of running a 64-bit kernel. We certainly don't see 64GB systems; maybe 8GB systems, but 64-bit registers are cheap and if you're willing to solder 8GB of RAM to the board, you're probably willing to splurge on a 64-bit ALU. The objection might be raised that kmap_local() is cheap, and it is. But when we have multi-page folios, particularly for filesystem metadata, it gets awkward to use kmap because it only supports individual pages; you can't kmap an entire folio. So I'd like to explore removing support for keeping filesystem metadata and page tables in highmem. Anon memory and file memory should probably remain supported in highmem. Interested?