From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752227AbcAUUAP (ORCPT ); Thu, 21 Jan 2016 15:00:15 -0500 Received: from mail-wm0-f45.google.com ([74.125.82.45]:35558 "EHLO mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751149AbcAUUAM (ORCPT ); Thu, 21 Jan 2016 15:00:12 -0500 From: Rasmus Villemoes To: Konrad Rzeszutek Wilk Cc: Julia Lawall , linux-mm@kvack.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org, Boris Ostrovsky , David Vrabel , xen-devel@lists.xenproject.org Subject: Re: [PATCH] cleancache: constify cleancache_ops structure Organization: D03 References: <1450904784-17139-1-git-send-email-Julia.Lawall@lip6.fr> <20160120222000.GA6765@char.us.oracle.com> X-Hashcash: 1:20:160121:konrad.wilk@oracle.com::0FKhSyA9nvqTrumO:0000000000000000000000000000000000000000rdE X-Hashcash: 1:20:160121:boris.ostrovsky@oracle.com::WiXu5+05eNl3beFr:0000000000000000000000000000000000001W5 X-Hashcash: 1:20:160121:julia.lawall@lip6.fr::wkG5H2xpes+4SeoL:000000000000000000000000000000000000000001JrK X-Hashcash: 1:20:160121:kernel-janitors@vger.kernel.org::IN3d/ubUB5+icXTg:0000000000000000000000000000001RMN X-Hashcash: 1:20:160121:linux-mm@kvack.org::u0ou/CalVMQG+PAH:00000000000000000000000000000000000000000001vc2 X-Hashcash: 1:20:160121:xen-devel@lists.xenproject.org::c/vF6GdGGPh1Vho8:00000000000000000000000000000003Ccm X-Hashcash: 1:20:160121:linux-kernel@vger.kernel.org::Rz/Nf38PnGX6b/8h:0000000000000000000000000000000002tIR X-Hashcash: 1:20:160121:david.vrabel@citrix.com::HMPreU2V38zygEIw:000000000000000000000000000000000000006SJj Date: Thu, 21 Jan 2016 21:00:09 +0100 In-Reply-To: <20160120222000.GA6765@char.us.oracle.com> (Konrad Rzeszutek Wilk's message of "Wed, 20 Jan 2016 17:20:00 -0500") Message-ID: <8760ymln3q.fsf@rasmusvillemoes.dk> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 20 2016, Konrad Rzeszutek Wilk wrote: > On Wed, Dec 23, 2015 at 10:06:24PM +0100, Julia Lawall wrote: >> The cleancache_ops structure is never modified, so declare it as const. >> >> This also removes the __read_mostly declaration on the cleancache_ops >> variable declaration, since it seems redundant with const. >> >> Done with the help of Coccinelle. >> >> Signed-off-by: Julia Lawall >> >> --- >> >> Not sure that the __read_mostly change is correct. Does it apply to the >> variable, or to what the variable points to? > > It should just put the structure in the right section (.rodata). > > Thanks for the patch! The __read_mostly marker should probably be left there... >> */ >> -static struct cleancache_ops *cleancache_ops __read_mostly; >> +static const struct cleancache_ops *cleancache_ops; >> >> /* >> * Counters available via /sys/kernel/debug/cleancache (if debugfs is >> @@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused) >> /* >> * Register operations for cleancache. Returns 0 on success. >> */ >> -int cleancache_register_ops(struct cleancache_ops *ops) >> +int cleancache_register_ops(const struct cleancache_ops *ops) >> { >> if (cmpxchg(&cleancache_ops, NULL, ops)) >> return -EBUSY; >> I don't know this code, but I assume that this is mostly a one-time thing, so once cleancache_ops gets its value assigned, it doesn't change, and that's what the __read_mostly is about (it applies to the object declared, not whatever it happens to point to). (Also, the commit message is slightly inaccurate: it is tmem_cleancache_ops which is never changed and hence declared const; changing the various pointers to it to const is just a necessary followup). Rasmus