From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id A92946B025F for ; Thu, 11 Jan 2018 19:43:19 -0500 (EST) Received: by mail-wr0-f198.google.com with SMTP id h20so2394888wrf.22 for ; Thu, 11 Jan 2018 16:43:19 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id v70si1409849wmd.97.2018.01.11.16.43.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Jan 2018 16:43:18 -0800 (PST) Date: Thu, 11 Jan 2018 16:43:15 -0800 From: Andrew Morton Subject: Re: [PATCH] mm/page_ext.c: Make page_ext_init a noop when CONFIG_PAGE_EXTENSION but nothing uses it Message-Id: <20180111164315.ca96f3ca533ee6684269d7f5@linux-foundation.org> In-Reply-To: <20180105130235.GA21241@techadventures.net> References: <20180105130235.GA21241@techadventures.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Oscar Salvador Cc: linux-mm@kvack.org, mhocko@suse.com, vbabka@suse.cz, jaewon31.kim@samsung.com On Fri, 5 Jan 2018 14:02:35 +0100 Oscar Salvador wrote: > static struct page_ext_operations *page_ext_ops[] always contains debug_guardpage_ops, > > static struct page_ext_operations *page_ext_ops[] = { > &debug_guardpage_ops, > #ifdef CONFIG_PAGE_OWNER > &page_owner_ops, > #endif > ... > } > > but for it to work, CONFIG_DEBUG_PAGEALLOC must be enabled first. > If someone has CONFIG_PAGE_EXTENSION, but has none of its users, > eg: (CONFIG_PAGE_OWNER, CONFIG_DEBUG_PAGEALLOC, CONFIG_IDLE_PAGE_TRACKING), we can shrink page_ext_init() > to a simple retq. > > $ size vmlinux (before patch) > text data bss dec hex filename > 14356698 5681582 1687748 21726028 14b834c vmlinux > > $ size vmlinux (after patch) > text data bss dec hex filename > 14356008 5681538 1687748 21725294 14b806e vmlinux > > On the other hand, it might does not even make sense, since if someone > enables CONFIG_PAGE_EXTENSION, I would expect him to enable also at least > one of its users, but I wanted to see what you guys think. Presumably the CONFIG_PAGE_EXTENSION users should `select' CONFIG_PAGE_EXTENSION so the situation doesn't arise. (or does it? I have a vague memory that if CONFIG_A selects CONFIG_B and you then set CONFIG_A=n, CONFIG_B remains enabled?) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org