From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753511AbcHPJxH (ORCPT ); Tue, 16 Aug 2016 05:53:07 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:34691 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753439AbcHPJxE (ORCPT ); Tue, 16 Aug 2016 05:53:04 -0400 Date: Tue, 16 Aug 2016 11:53:01 +0200 From: Michal Hocko To: js1304@gmail.com Cc: Andrew Morton , Vlastimil Babka , Minchan Kim , Sergey Senozhatsky , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Joonsoo Kim Subject: Re: [PATCH v2 0/6] Reduce memory waste by page extension user Message-ID: <20160816095300.GC17417@dhcp22.suse.cz> References: <1471315879-32294-1-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1471315879-32294-1-git-send-email-iamjoonsoo.kim@lge.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 16-08-16 11:51:13, Joonsoo Kim wrote: > From: Joonsoo Kim > > v2: > Fix rebase mistake (per Vlastimil) > Rename some variable/function to prevent confusion (per Vlastimil) > Fix header dependency (per Sergey) > > This patchset tries to reduce memory waste by page extension user. > > First case is architecture supported debug_pagealloc. It doesn't > requires additional memory if guard page isn't used. 8 bytes per > page will be saved in this case. > > Second case is related to page owner feature. Until now, if page_ext > users want to use it's own fields on page_ext, fields should be > defined in struct page_ext by hard-coding. It has a following problem. > > struct page_ext { > #ifdef CONFIG_A > int a; > #endif > #ifdef CONFIG_B > int b; > #endif > }; > > Assume that kernel is built with both CONFIG_A and CONFIG_B. > Even if we enable feature A and doesn't enable feature B at runtime, > each entry of struct page_ext takes two int rather than one int. > It's undesirable waste so this patch tries to reduce it. By this patchset, > we can save 20 bytes per page dedicated for page owner feature > in some configurations. FWIW I like this. I have only glanced over those patches so I do not feel comfortable to give my a-b but the approach is sensible and the memory savings are really attractive. Page owner is a really great debugging feauture so enabling it makes a lot of sense on production servers where the memory wasting is a no-go. Thanks! -- Michal Hocko SUSE Labs