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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 08EE5C4338F for ; Mon, 9 Aug 2021 11:23:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D1614601FD for ; Mon, 9 Aug 2021 11:23:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235114AbhHILYH (ORCPT ); Mon, 9 Aug 2021 07:24:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59106 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234930AbhHILYF (ORCPT ); Mon, 9 Aug 2021 07:24:05 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B088C0613D3 for ; Mon, 9 Aug 2021 04:23:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ZQlR1NWfHc+K2Vy1e2qCq+hN81CMxlQnYLSgBZIPQtI=; b=vE/x5V/fQGAhEsUx/0Tq/oFp+8 8qfJ1r70h1lFCEfpcF3WVqLy+X6C4CYvVpfu5Hqpsb1+HqdI4PWBkvXg5GN7C9tfiacnedxtzb9uw 27IwLkwx5gbEr5T1CYXsbgv8MaHJ8zaMbnXWYoNvFIAi8HIuZPUlJx0Im6FUtu/x/CmJhLh5Kj1u7 uY0jAGC84TCRhLuy5L3OCiB2MLJ01+H7EfgbJCABLlu2Boe4LXBTZ2C29L2LqcqVEM1Cizy+mgA+U 8P5xWjNSRTDdC0cYdOCnw7U74higL7DAztsHHHCagXcBC46tfLd4Hrps4KySWHp0mhEIuKFn+0fIw L6l5grFg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mD3M9-00AwAT-BA; Mon, 09 Aug 2021 11:22:28 +0000 Date: Mon, 9 Aug 2021 12:22:09 +0100 From: Matthew Wilcox To: Hugh Dickins Cc: Zi Yan , Vlastimil Babka , David Hildenbrand , linux-mm@kvack.org, "Kirill A . Shutemov" , Mike Kravetz , Michal Hocko , John Hubbard , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time parameter. Message-ID: References: <20210805190253.2795604-1-zi.yan@sent.com> <0d374eed-cc52-a656-b338-1156782bdf7e@suse.cz> <6ae6cd92-3ff4-7ed3-b337-a4dfe33da1c@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 08, 2021 at 09:29:29PM -0700, Hugh Dickins wrote: > On Sat, 7 Aug 2021, Matthew Wilcox wrote: > > > > I am, however, of the opinion that 2MB pages give us so much trouble > > because they're so very special. Few people exercise those code paths and > > it's easy to break them without noticing. This is partly why I want to > > do arbitrary-order pages. If everybody is running with compound pages > > all the time, we'll see the corner cases often, and people other than > > Hugh, Kirill and Mike will be able to work on them. > > I don't entirely agree. I'm all for your use of compound pages in page > cache, but don't think its problems are representative of the problems > in aiming for a PMD (or PUD) bar, with the weird page table transitions > we expect of "THP" there. > > I haven't checked: is your use of compound pages in page cache still > limited to the HAVE_ARCH_TRANSPARENT_HUGEPAGE architectures? When > the others could just as well use compound pages in page cache too. It is no longer gated by whether TRANSPARENT_HUGEPAGE is enabled or not. That's a relatively recent change, and I can't say that I've tested it. I'll give it a try today on a PA-RISC system I've booted recently. One of the followup pieces of work that I hope somebody other than myself will undertake is using 64KB PTEs on a 4KB PAGE_SIZE ARM/POWER machine if the stars align.