From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 78D236B004A for ; Wed, 6 Oct 2010 21:00:57 -0400 (EDT) Date: Thu, 7 Oct 2010 09:54:58 +0900 From: Daisuke Nishimura Subject: Re: [RFC] Restrict size of page_cgroup->flags Message-Id: <20101007095458.a992969e.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20101006142314.GG4195@balbir.in.ibm.com> References: <20101006142314.GG4195@balbir.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: balbir@linux.vnet.ibm.com Cc: KAMEZAWA Hiroyuki , containers@lists.linux-foundation.org, "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Daisuke Nishimura List-ID: On Wed, 6 Oct 2010 19:53:14 +0530 Balbir Singh wrote: > I propose restricting page_cgroup.flags to 16 bits. The patch for the > same is below. Comments? > > > Restrict the bits usage in page_cgroup.flags > > From: Balbir Singh > > Restricting the flags helps control growth of the flags unbound. > Restriciting it to 16 bits gives us the possibility of merging > cgroup id with flags (atomicity permitting) and saving a whole > long word in page_cgroup > I agree that reducing the size of page_cgroup would be good and important. But, wouldn't it be better to remove ->page, if possible ? Thanks, Daisuke Nishimura. > Signed-off-by: Balbir Singh > --- > > include/linux/page_cgroup.h | 3 +++ > mm/page_cgroup.c | 1 + > 2 files changed, 4 insertions(+), 0 deletions(-) > > > diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h > index 872f6b1..10c37b4 100644 > --- a/include/linux/page_cgroup.h > +++ b/include/linux/page_cgroup.h > @@ -44,8 +44,11 @@ enum { > PCG_FILE_WRITEBACK, /* page is under writeback */ > PCG_FILE_UNSTABLE_NFS, /* page is NFS unstable */ > PCG_MIGRATION, /* under page migration */ > + PCG_MAX_NR, > }; > > +#define PCG_MAX_BIT_SIZE 16 > + > #define TESTPCGFLAG(uname, lname) \ > static inline int PageCgroup##uname(struct page_cgroup *pc) \ > { return test_bit(PCG_##lname, &pc->flags); } > diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c > index 5bffada..e16ad2e 100644 > --- a/mm/page_cgroup.c > +++ b/mm/page_cgroup.c > @@ -258,6 +258,7 @@ void __init page_cgroup_init(void) > unsigned long pfn; > int fail = 0; > > + BUILD_BUG_ON(PCG_MAX_NR >= PCG_MAX_BIT_SIZE); > if (mem_cgroup_disabled()) > return; > > > -- > Three Cheers, > Balbir > > -- > 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 > -- 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