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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 3F9C4C433FE for ; Sun, 6 Dec 2020 11:56:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0333A22AAD for ; Sun, 6 Dec 2020 11:56:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727646AbgLFL4D (ORCPT ); Sun, 6 Dec 2020 06:56:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:52020 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725767AbgLFL4D (ORCPT ); Sun, 6 Dec 2020 06:56:03 -0500 Date: Sun, 6 Dec 2020 13:55:17 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607255723; bh=pTpsXS9CBriukmpy9E70AdN9gCV7E3J/symznTMEUrg=; h=From:To:Cc:Subject:References:In-Reply-To:From; b=RXZ0B/nzOzWsaFVRvI6ZjRbJ6wLRT2dJpYT4Dt7VBca4QCoJuM5SAZWP1N9Pu/zwP L0kazA7TFH12wCnfSkkCxQTRejZRN8sxziNtu3cB7pIooUdr68wQNcKzu54/fLE5zu xnwwI8rDDYJtXoAFUd/xAh6zMjUP65QQ1iibZRGBVu0IejhJOk+5a9T5MYS+Iq2tq2 LvLFHCJWkIYU2MhLSN7IH7KJ8FC2fSJFiDiuhmU371o+pDxHUv8Z6uhPNWeqXyu2qR lXPXaJio9ZOXl85oNHrlnop5TKKk/ADvXD+jDklROb25kQ8o30K/7mtfnMe3MtzZKE ZrP/4TuXtqjxg== From: Mike Rapoport To: carver4lio@163.com Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hailong Liu Subject: Re: [PATCH] mm/memblock:use a more appropriate order calculation when free memblock pages Message-ID: <20201206115517.GL751215@kernel.org> References: <20201203152311.5272-1-carver4lio@163.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201203152311.5272-1-carver4lio@163.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 03, 2020 at 11:23:10PM +0800, carver4lio@163.com wrote: > From: Hailong Liu > > When system in the booting stage, pages span from [start, end] of a memblock > are freed to buddy in a order as large as possible (less than MAX_ORDER) at > first, then decrease gradually to a proper order(less than end) in a loop. > > However, *min(MAX_ORDER - 1UL, __ffs(start))* can not get the largest order > in some cases. Do you have examples? What is the memory configration that casues suboptimal order selection and what is the order in this case? > Instead, *__ffs(end - start)* may be more appropriate and meaningful. As several people reported using __ffs(end - start) is not correct. If the order selection is indeed suboptimal we'd need some better formula ;-) > Signed-off-by: Hailong Liu > --- > mm/memblock.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memblock.c b/mm/memblock.c > index b68ee8678..7c6d0dde7 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -1931,7 +1931,7 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end) > int order; > > while (start < end) { > - order = min(MAX_ORDER - 1UL, __ffs(start)); > + order = min(MAX_ORDER - 1UL, __ffs(end - start)); > > while (start + (1UL << order) > end) > order--; > -- > 2.17.1 > > -- Sincerely yours, Mike.