From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx198.postini.com [74.125.245.198]) by kanga.kvack.org (Postfix) with SMTP id 0FFAB6B004D for ; Mon, 19 Mar 2012 18:21:00 -0400 (EDT) Received: by yhr47 with SMTP id 47so7577166yhr.14 for ; Mon, 19 Mar 2012 15:20:56 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <4F66E7D7.4040406@jp.fujitsu.com> References: <4F66E6A5.10804@jp.fujitsu.com> <4F66E7D7.4040406@jp.fujitsu.com> Date: Mon, 19 Mar 2012 15:20:55 -0700 Message-ID: Subject: Re: [RFC][PATCH 2/3] memcg: reduce size of struct page_cgroup. From: Suleiman Souhlal Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Hugh Dickins , Han Ying , Glauber Costa , "Aneesh Kumar K.V" , Andrew Morton , n-horiguchi@ah.jp.nec.com, khlebnikov@openvz.org, Tejun Heo 2012/3/19 KAMEZAWA Hiroyuki : > Now, page_cgroup->flags has only 3bits. Considering alignment of > struct mem_cgroup, which is allocated by kmalloc(), we can encode > pointer to mem_cgroup and flags into a word. > > After this patch, pc->flags is encoded as > > =A063 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 2 =A0 =A0 0 > =A0| pointer to memcg..........|flags| > > Signed-off-by: KAMEZAWA Hiroyuki > --- > =A0include/linux/page_cgroup.h | =A0 15 ++++++++++++--- > =A01 files changed, 12 insertions(+), 3 deletions(-) > > diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h > index 92768cb..bca5447 100644 > --- a/include/linux/page_cgroup.h > +++ b/include/linux/page_cgroup.h > @@ -1,6 +1,10 @@ > =A0#ifndef __LINUX_PAGE_CGROUP_H > =A0#define __LINUX_PAGE_CGROUP_H > > +/* > + * Because these flags are encoded into ->flags with a pointer, > + * we cannot have too much flags. > + */ > =A0enum { > =A0 =A0 =A0 =A0/* flags for mem_cgroup */ > =A0 =A0 =A0 =A0PCG_LOCK, =A0/* Lock for pc->mem_cgroup and following bits= . */ > @@ -9,6 +13,8 @@ enum { > =A0 =A0 =A0 =A0__NR_PCG_FLAGS, > =A0}; > > +#define PCG_FLAGS_MASK ((1 << __NR_PCG_FLAGS) - 1) > + > =A0#ifndef __GENERATING_BOUNDS_H > =A0#include > > @@ -21,10 +27,12 @@ enum { > =A0* page_cgroup helps us identify information about the cgroup > =A0* All page cgroups are allocated at boot or memory hotplug event, > =A0* then the page cgroup for pfn always exists. > + * > + * flags and a pointer to memory cgroup are encoded into ->flags. > + * Lower 3bits are used for flags and others are used for a pointer to m= emcg. Would it be worth adding a BUILD_BUG_ON(__NR_PCG_FLAGS > 3) ? -- Suleiman -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org