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=-3.9 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 BF2E1C433E2 for ; Wed, 9 Sep 2020 11:24:17 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E643C21D7B for ; Wed, 9 Sep 2020 11:24:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="SmXDZKzA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E643C21D7B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 6AF906B0002; Wed, 9 Sep 2020 07:24:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 660546B0003; Wed, 9 Sep 2020 07:24:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 575F06B005A; Wed, 9 Sep 2020 07:24:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0175.hostedemail.com [216.40.44.175]) by kanga.kvack.org (Postfix) with ESMTP id 42B7E6B0002 for ; Wed, 9 Sep 2020 07:24:16 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id F255F1EF2 for ; Wed, 9 Sep 2020 11:24:15 +0000 (UTC) X-FDA: 77243289270.08.talk42_2812219270dd Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id C97DB1819E769 for ; Wed, 9 Sep 2020 11:24:15 +0000 (UTC) X-HE-Tag: talk42_2812219270dd X-Filterd-Recvd-Size: 4302 Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Wed, 9 Sep 2020 11:24:14 +0000 (UTC) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4BmfmN3SGmz9sTd; Wed, 9 Sep 2020 21:24:04 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1599650649; bh=McxY0vGyvNVlrIIx6KzYtU4PcHnFzd9G9dek0Ykf36c=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=SmXDZKzAAkIskfZPfi7qrbi2STOAaRgkLgLUwpRIri563PnPrs5blw/OlSwl2MX5i 69HKj9JHLONl1Qz3CbYvZy/4cbddpiJHmROqXSbmg8WJh+BTuQXH9dKNRHILZpAo1t hze5cgR0ZcFpNy/5f5QSzsCR/ywLKY3MFV1MB2evwZ2HPd+YxWui6TnWbMXUjz3bFE Dflejkj7ciOj6dUGOWs0UizA/kfuOX43D8JH9M1T139ttlnt9G8+OPWPLzwt3iVOxx uuXIzjXH4T67FDy3bvc2QCqjoeC0dD5axnVjQL4imxfeD2KhwwbuLyb1WJFKSm2qYS /CHKbJLh3kYdA== From: Michael Ellerman To: David Hildenbrand , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, linux-hyperv@vger.kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org, linux-nvdimm@lists.01.org, linux-s390@vger.kernel.org, Andrew Morton , Wei Liu , Michal Hocko , Dan Williams , Jason Gunthorpe , Pankaj Gupta , Baoquan He , Wei Yang , Benjamin Herrenschmidt , Paul Mackerras , "Rafael J. Wysocki" , Len Brown , Vishal Verma , Dave Jiang , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , "Michael S. Tsirkin" , Jason Wang , Boris Ostrovsky , Juergen Gross , Stefano Stabellini , Oliver O'Halloran , Pingfan Liu , Nathan Lynch , Libor Pechacek , Anton Blanchard , Leonardo Bras , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v2 3/7] mm/memory_hotplug: prepare passing flags to add_memory() and friends In-Reply-To: <3bc5b464-3229-d442-714a-ec33b5728ac6@redhat.com> References: <20200908201012.44168-1-david@redhat.com> <20200908201012.44168-4-david@redhat.com> <20200909071759.GD435421@kroah.com> <3bc5b464-3229-d442-714a-ec33b5728ac6@redhat.com> Date: Wed, 09 Sep 2020 21:24:02 +1000 Message-ID: <87eenbry5p.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: C97DB1819E769 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: David Hildenbrand writes: > On 09.09.20 09:17, Greg Kroah-Hartman wrote: >> On Tue, Sep 08, 2020 at 10:10:08PM +0200, David Hildenbrand wrote: >>> We soon want to pass flags, e.g., to mark added System RAM resources. >>> mergeable. Prepare for that. >> >> What are these random "flags", and how do we know what should be passed >> to them? >> >> Why not make this an enumerated type so that we know it all works >> properly, like the GPF_* flags are? Passing around a random unsigned >> long feels very odd/broken... > > Agreed, an enum (mhp_flags) seems to give a better hint what can > actually be passed. Thanks! You probably know this but ... Just using a C enum doesn't get you any type safety. You can get some checking via sparse by using __bitwise, which is what gfp_t does. You don't actually have to use an enum for that, it works with #defines also. Or you can wrap the flag in a struct, the way atomic_t does, and then the compiler will prevent passing plain integers in place of your custom type. cheers