From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f42.google.com (mail-wg0-f42.google.com [74.125.82.42]) by kanga.kvack.org (Postfix) with ESMTP id D31586B00F2 for ; Mon, 3 Nov 2014 16:52:15 -0500 (EST) Received: by mail-wg0-f42.google.com with SMTP id k14so12195804wgh.15 for ; Mon, 03 Nov 2014 13:52:15 -0800 (PST) Received: from jenni1.inet.fi (mta-out1.inet.fi. [62.71.2.227]) by mx.google.com with ESMTP id na16si9961001wic.20.2014.11.03.13.52.14 for ; Mon, 03 Nov 2014 13:52:14 -0800 (PST) Date: Mon, 3 Nov 2014 23:52:06 +0200 From: "Kirill A. Shutemov" Subject: Re: [patch 1/3] mm: embed the memcg pointer directly into struct page Message-ID: <20141103215206.GB24091@node.dhcp.inet.fi> References: <1414898156-4741-1-git-send-email-hannes@cmpxchg.org> <20141103210607.GA24091@node.dhcp.inet.fi> <20141103213628.GA11428@phnom.home.cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141103213628.GA11428@phnom.home.cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Michal Hocko , Vladimir Davydov , Tejun Heo , David Miller , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, Nov 03, 2014 at 04:36:28PM -0500, Johannes Weiner wrote: > On Mon, Nov 03, 2014 at 11:06:07PM +0200, Kirill A. Shutemov wrote: > > On Sat, Nov 01, 2014 at 11:15:54PM -0400, Johannes Weiner wrote: > > > Memory cgroups used to have 5 per-page pointers. To allow users to > > > disable that amount of overhead during runtime, those pointers were > > > allocated in a separate array, with a translation layer between them > > > and struct page. > > > > > > There is now only one page pointer remaining: the memcg pointer, that > > > indicates which cgroup the page is associated with when charged. The > > > complexity of runtime allocation and the runtime translation overhead > > > is no longer justified to save that *potential* 0.19% of memory. > > > > How much do you win by the change? > > Heh, that would have followed right after where you cut the quote: > with CONFIG_SLUB, that pointer actually sits in already existing > struct page padding, which means that I'm saving one pointer per page > (8 bytes per 4096 byte page, 0.19% of memory), plus the pointer and > padding in each memory section. I also save the (minor) translation > overhead going from page to page_cgroup and the maintenance burden > that stems from having these auxiliary arrays (see deleted code). I read the description. I want to know if runtime win (any benchmark data?) from moving mem_cgroup back to the struct page is measurable. If the win is not significant, I would prefer to not occupy the padding: I'm sure we will be able to find a better use for the space in struct page in the future. -- Kirill A. Shutemov -- 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