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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 07C29C4320A for ; Mon, 9 Aug 2021 04:29:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC2B461019 for ; Mon, 9 Aug 2021 04:29:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232894AbhHIE3z (ORCPT ); Mon, 9 Aug 2021 00:29:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229483AbhHIE3x (ORCPT ); Mon, 9 Aug 2021 00:29:53 -0400 Received: from mail-oi1-x231.google.com (mail-oi1-x231.google.com [IPv6:2607:f8b0:4864:20::231]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6A8BC06175F for ; Sun, 8 Aug 2021 21:29:33 -0700 (PDT) Received: by mail-oi1-x231.google.com with SMTP id y18so21884869oiv.3 for ; Sun, 08 Aug 2021 21:29:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :mime-version; bh=x6px4cJEMUh0LSKzJ+O2PybgqRw98ylZHdAHYBrlzPo=; b=ugbfYuMFVxaD3nAdyTA+EH+lP3+SPqNcfqUVCUmRLBE8e04+aOCKAUP9jm98J+Ybh1 0/TgUB2cbUSS2yL2nb32a8coFWcYPTKNlMNTGKKDK7TqjHIVkhmKljfeC/anOwjvoJw2 +f3BonQgf6C5fEfElQsltvz5w98FZWabRLR9yNZde10NbgGmmsVYUqFDDUt0DW4fFlLo DSCsVZHllceFsK3ZFtzpBsIRTglJP+JlOh1y2ZDFTrDuydhC8R+9lmBPTM9ozumfQu1L dbMOc4QHgclfSo3DPe+RuWWpRvIopEpOzjmLuvzZt3PPlpsHg2OQpDas1h2s7HiXLNB1 DT6g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:mime-version; bh=x6px4cJEMUh0LSKzJ+O2PybgqRw98ylZHdAHYBrlzPo=; b=f33sb8xzKafwFZ9ssKgROU0KVVCGgaBVZ66aB3TgYHktrSb/Lkk3RcOT1JDuzeqhat IQDRXQN4gUVrOHSjeQPwSdw1lnbrjKeQpQw5Zox3pgFC9YNZCJgy31o1XNJ6V40D1RhG lXDb5fyU5J3ieYeQHSVuwj1PQAD9T2XG9zInnRKsqXd7L59mErsY+eNwxS0E/NtbKxWK CGoLyRfOfmOdLaA3jX8yy8NsR3iQc2PD3eofn8v8EPu/H05vQFhsoAnrK4vBHsv2tI8/ X3t89mVobLZZ8mBW2uUzVybNUx3zk4Ef96SJYJs5w1psVIFZL/cj1ChswtQsvRU7vpXc vGQQ== X-Gm-Message-State: AOAM5316ziMRHygpmLARJPGlIZ12eBVC+923GGE18sYiTZ/Xy2Uts+5G N+qhV+23SEW2mjNoLrXCJ8neJA== X-Google-Smtp-Source: ABdhPJyPupTwRb5MNdzD1P8iHXEWiHVXy7eVfAPFKzJGnzzTYrjtP0dvZnuCymcetr+uuk++XTr25Q== X-Received: by 2002:a05:6808:bcd:: with SMTP id o13mr23116015oik.61.1628483372998; Sun, 08 Aug 2021 21:29:32 -0700 (PDT) Received: from ripple.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id x16sm2667189ooj.1.2021.08.08.21.29.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Aug 2021 21:29:32 -0700 (PDT) Date: Sun, 8 Aug 2021 21:29:29 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: Matthew Wilcox cc: Hugh Dickins , 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. In-Reply-To: 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Hugh