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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 917BCC54E94 for ; Thu, 26 Jan 2023 08:00:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233024AbjAZIAU (ORCPT ); Thu, 26 Jan 2023 03:00:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235509AbjAZIAR (ORCPT ); Thu, 26 Jan 2023 03:00:17 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E1FC169B2C for ; Wed, 25 Jan 2023 23:59:45 -0800 (PST) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 702451FEC1; Thu, 26 Jan 2023 07:59:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1674719984; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8phw8z9lSY7iQJCq6VYkn4UUEHCEZ7ZXKi1c7gTwrM4=; b=qTWifsp9kR6tUF5RbmZkPrFSDZSuoNzYFU4i42xM+2e0bl32CICy762Ehn1A7cN9EuqmJ0 AZkmevMfJIwKOy1HC8U/GL4eP9OHTN67Q3TI95rlLJfzptW0842juEEEyO6mRIlygvAJd6 Y1BtkkMiEmx1HmgPqlW1Wt0jsVYn2mI= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 42F671358A; Thu, 26 Jan 2023 07:59:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id rFjmD/Ay0mMFJwAAMHmgww (envelope-from ); Thu, 26 Jan 2023 07:59:44 +0000 Date: Thu, 26 Jan 2023 08:59:43 +0100 From: Michal Hocko To: Suren Baghdasaryan Cc: Andrew Morton , michel@lespinasse.org, jglisse@google.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 2/7] mm: introduce vma->vm_flags wrapper functions Message-ID: References: <20230125233554.153109-1-surenb@google.com> <20230125233554.153109-3-surenb@google.com> <20230125162810.ec222773d13cd26c55991fde@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 25-01-23 16:56:17, Suren Baghdasaryan wrote: > On Wed, Jan 25, 2023 at 4:28 PM Andrew Morton wrote: > > > > On Wed, 25 Jan 2023 15:35:49 -0800 Suren Baghdasaryan wrote: > > > > > --- a/include/linux/mm_types.h > > > +++ b/include/linux/mm_types.h > > > @@ -491,7 +491,15 @@ struct vm_area_struct { > > > * See vmf_insert_mixed_prot() for discussion. > > > */ > > > pgprot_t vm_page_prot; > > > - unsigned long vm_flags; /* Flags, see mm.h. */ > > > + > > > + /* > > > + * Flags, see mm.h. > > > + * To modify use {init|reset|set|clear|mod}_vm_flags() functions. > > > + */ > > > + union { > > > + const vm_flags_t vm_flags; > > > + vm_flags_t __private __vm_flags; > > > + }; > > > > Typically when making a change like this we'll rename the affected > > field/variable/function/etc. This will reliably and deliberately break > > unconverted usage sites. > > > > This const trick will get us partway there, by breaking setters. But > > renaming it will break both setters and getters. > > My intent here is to break setters but to allow getters to keep > reading vma->vm_flags directly. We could provide get_vm_flags() and > convert all getters as well but it would introduce a huge additional > churn (800+ hits) with no obvious benefits, I think. Does that clarify > the intent of this trick? I think that makes sense at this stage. The conversion patch is quite large already. Maybe the final renaming could be done on top of everything and patch generated by coccinele. The const union is a neat trick but a potential lockdep assert is a nice plus as well. I wouldn't see it as a top priority though. -- Michal Hocko SUSE Labs