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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 32ADCC35254 for ; Wed, 5 Feb 2020 12:52:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id F173A2072B for ; Wed, 5 Feb 2020 12:52:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F173A2072B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 748466B0005; Wed, 5 Feb 2020 07:52:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6F8536B0006; Wed, 5 Feb 2020 07:52:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 60D466B0007; Wed, 5 Feb 2020 07:52:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0063.hostedemail.com [216.40.44.63]) by kanga.kvack.org (Postfix) with ESMTP id 479536B0005 for ; Wed, 5 Feb 2020 07:52:00 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 0E28E181AC9CC for ; Wed, 5 Feb 2020 12:52:00 +0000 (UTC) X-FDA: 76456060800.15.crow30_1165eeda43c58 X-HE-Tag: crow30_1165eeda43c58 X-Filterd-Recvd-Size: 3280 Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by imf35.hostedemail.com (Postfix) with ESMTP for ; Wed, 5 Feb 2020 12:51:59 +0000 (UTC) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 015CppFf030570; Wed, 5 Feb 2020 06:51:51 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 015Cpn3x030569; Wed, 5 Feb 2020 06:51:49 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 5 Feb 2020 06:51:49 -0600 From: Segher Boessenkool To: David Hildenbrand Cc: Oscar Salvador , linux-s390@vger.kernel.org, Michal Hocko , linux-ia64@vger.kernel.org, Pavel Tatashin , linux-sh@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Wei Yang , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Dan Williams , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages() Message-ID: <20200205125149.GS22482@gate.crashing.org> References: <20191006085646.5768-1-david@redhat.com> <20191006085646.5768-11-david@redhat.com> <20200204094652.GE6494@linux> <5d698f94-af18-0714-bc97-14b6c520572c@redhat.com> <20200204131353.GJ22482@gate.crashing.org> <0e2f700c-b01b-8c16-99c2-2648967fc203@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0e2f700c-b01b-8c16-99c2-2648967fc203@redhat.com> User-Agent: Mutt/1.4.2.3i X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Feb 04, 2020 at 02:38:51PM +0100, David Hildenbrand wrote: > On 04.02.20 14:13, Segher Boessenkool wrote: > > On Tue, Feb 04, 2020 at 01:41:06PM +0100, David Hildenbrand wrote: > >> It's a pattern commonly used in compilers and emulators to calculate the > >> number of bytes to the next block/alignment. (we're missing a macro > >> (like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up > >> with a good name (e.g., SIZE_TO_NEXT_ALIGN) . > > You can just write the easy to understand > > > > ... ALIGN_UP(x) - x ... > > you mean > > ALIGN_UP(x, PAGES_PER_SECTION) - x > > but ... > > > which is better *without* having a separate name. Does that not > > generate good machine code for you? > > 1. There is no ALIGN_UP. "SECTION_ALIGN_UP(x) - x" would be possible Erm, you started it ;-) > 2. It would be wrong if x is already aligned. > > e.g., let's use 4096 for simplicity as we all know that value by heart > (for both x and the block size). > > a) -(4096 | -4096) -> 4096 > > b) #define ALIGN_UP(x, a) ((x + a - 1) & -(a)) > > ALIGN_UP(4096, 4096) - 4096 -> 0 > > Not as easy as it seems ... If you always want to return a number >= 1, it it simply ALIGN_UP(x + 1) - x (and replace 1 by any other minimum size required). This *also* is easy to read, without having to have any details (and quirks :-/ ) of those utility functions memorised. Segher