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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 887FAC07E99 for ; Fri, 9 Jul 2021 07:13:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 68D68610FB for ; Fri, 9 Jul 2021 07:13:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230409AbhGIHP5 (ORCPT ); Fri, 9 Jul 2021 03:15:57 -0400 Received: from mout.gmx.net ([212.227.15.19]:53417 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230121AbhGIHP4 (ORCPT ); Fri, 9 Jul 2021 03:15:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1625814775; bh=JAl6Zi1wOiNbZiUmdKMd3T6NLQtnUuhXz1w4Hnp5SYk=; h=X-UI-Sender-Class:Subject:To:Cc:References:From:Date:In-Reply-To; b=GLOo48x6I4mG7l1BMboTZdecGYYmITnKg9hEK9mz/oIXwj6q9IT13A0v7Cp/vqre/ MGDhTxhunZuH0wPyg3bUmHOXHo/fbqO7mOgKx81Ii/9iDpYpcS0uq/4bDifEM8AqaG bp72S/D4Zw1R4ACxpakzeAVvMS5k7vVQtDKcn79c= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [0.0.0.0] ([149.28.201.231]) by mail.gmx.net (mrgmx005 [212.227.17.184]) with ESMTPSA (Nemesis) id 1MLzBj-1ljoIh1qAD-00Hz4a; Fri, 09 Jul 2021 09:12:55 +0200 Subject: Re: [PATCH 0/6] Remove highmem allocations, kmap/kunmap To: Christoph Hellwig Cc: Neal Gompa , David Sterba , Btrfs BTRFS References: From: Qu Wenruo Message-ID: Date: Fri, 9 Jul 2021 15:12:50 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:wLB/sI7uefEp1C+VKfIKGqe5mA9H5YCq0TlaVOWfaZExxmziDWz Hl7cXB3p8xAPsQ6p+dxxUy6qWM2dFhE7MPpIEYciGYf8jqhtdAlXt17JSOUQgkv3J4xUOjg noJIewt5QpzKYEXPgB1kdhExh3NNeNSJttwCM/KpAccttnOGAhzEXYCa/CFnQX96gCyygbT 6HpObxXd+0gzezT09lgDw== X-UI-Out-Filterresults: notjunk:1;V03:K0:VAXxrW6lbMY=:C4WU0EmBHykpYG5wqJE3sr 4b+7J5ntlY6dTTb2O5rwZ23wIwTt8OAf4lPhOvYEsVxHK7T5wIvXNkcO76lqsQzvA2nhzN3xx 2/OgZt19mIuc44f+EawCz37iZVt+eEkPCHZRd5P/GClBoBL+6nz6cUCObs8tkhxI3bmEY2/JD CxdMbMNpa7Gtr6CaMOYebV9ugxFoAmFYmLjG9xoe//rzypnoxqv7WSg8R+0wF9CZR6e5TuNQV GOZJ+Mc1fB0vN1TV1pvQtKRLuT2UwJA5V7sQl188WJklsmg/CDbNXPolfhCLcCHArGuuhKE2G hw0pdely9LsPwYEfoUQmAk72I9tBt9ddmwDsNW7h5PeHF9Je5/6s63cioqOrNUZOCGulIhvmK tOrm5tZlhDHH2X/vCD+cvhHD5D9BB/BV+zaV8bbEK9jYb+kDfphO25FuwcI/FjSJSaXodWDWk WKz8+e/Ryz193aBXl6U/j1d9Ql1Ovncv9KZkarFoN7Oa0m0dBEbe4jlQf64o57BYFio+eSpXJ z4e5MGuLhIZ7VDq6h9lo4eeqPc0au3BBY73Vf2ZHmidgFT5YT77lQEqAEwBOJu0GwLluJXhoE BpXbjQrb85P4eI1LJcdiF4KyeZIL6g1WYi67fYl7H9spbdpN7hXU1/uSVvzCiEQS/NmT74AKq jX27bnR1Oyi0hRuqrM/ZjF+nyNcIFcuDddN2hwvNXc9cBLxaN2Hn7XsreehyIqdsA9uZYX2a8 BRHBmojeJ4k8o4EDdINysZsbtLCZ8oUz1dT9/WKml0ygKkKDEAgMqjh0AQ5193m2pcne0kVIh LJ/OE5YVb5T/Xwm8FhlVCrhNuHWOp/WSL5U59xXGGP+j5MsqqJxZ3KdQ6QBPETRmvuag0EGQk 0vv5GN8zn0H4mhz9zwE9P4TxQYRhQftpnidBzN5fayb9XUFYvo+ay+7Hv0de+Yax0/nTcvaIW Qf1uuTxaqPcC7DkZIl5zTPPhpMibpeVFEdVj+vLHSIpXSARxzMwv2FvjQ6mKX2Xq8CM5mUJ8z S53Tj/e3+boZcKsV9nWUxoFAiWBs45f0Tt8wQ5E0vqHQdD3433JOBQyXwm2+pfRgTTXFiJBkl zdwxUzIGN+AZnUQPR1OJ0HepW67eEPwA4eEMffojbv3KdB61KTBulrLLA== Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2021/7/9 =E4=B8=8B=E5=8D=882:46, Christoph Hellwig wrote: > On Fri, Jul 09, 2021 at 07:53:39AM +0800, Qu Wenruo wrote: >> Sorry, I can't see the reason why it would cause performance drop or >> higher memory usage. >> >> The point of HIGHMEM is to work on archs where system can only access >> memory below 4G reliably, any memory above 4G must be manually mapped >> into the 4G range before access. >> >> AFAIK it's only x86 using PAE needs this, and none of the ARM SoC uses >> such feature. > > Arm calls it LPAE, but otherwise it is the same. > Yeah, and I have never seen any toy ARM boards using LPAE neither. Either those boards have too small memory to bother (<=3D 4G), or they go directly aarch64. (And most boards are even aarch64 with <=3D 4G ram, like RK3399 or Amlogic SoCs, they are aarch64 but only support up to 4G physical RAM). Way less historical burden here. Thanks, Qu