From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753343Ab0JGFbY (ORCPT ); Thu, 7 Oct 2010 01:31:24 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:46622 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752382Ab0JGFbW (ORCPT ); Thu, 7 Oct 2010 01:31:22 -0400 Date: Thu, 7 Oct 2010 11:01:17 +0530 From: Balbir Singh To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , containers@lists.linux-foundation.org, "linux-kernel@vger.kernel.org" Subject: Re: [RFC] Restrict size of page_cgroup->flags Message-ID: <20101007053117.GQ4195@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20101006142314.GG4195@balbir.in.ibm.com> <20101007085858.0e07de59.kamezawa.hiroyu@jp.fujitsu.com> <20101007031203.GK4195@balbir.in.ibm.com> <20101007121816.bbd009c1.kamezawa.hiroyu@jp.fujitsu.com> <20101007035608.GN4195@balbir.in.ibm.com> <20101007132233.f695aa2c.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20101007132233.f695aa2c.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * KAMEZAWA Hiroyuki [2010-10-07 13:22:33]: > On Thu, 7 Oct 2010 09:26:08 +0530 > Balbir Singh wrote: > > > * KAMEZAWA Hiroyuki [2010-10-07 12:18:16]: > > > > > On Thu, 7 Oct 2010 08:42:04 +0530 > > > Balbir Singh wrote: > > > > > > > * KAMEZAWA Hiroyuki [2010-10-07 08:58:58]: > > > > > > > > > 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 > > > > > > > > > > > > Signed-off-by: Balbir Singh > > > > > > > > > > Doesn't make sense until you show the usage of existing bits. > > > > > > > > ?? > > > > > > > Limiting something for NOT EXISTING PATCH doesn't make sense, in general. > > > > > > > > > > > And I guess 16bit may be too large on 32bit systems. > > > > > > > > too large on 32 bit systems? My intention is to keep the flags to 16 > > > > bits and then use cgroup id for the rest and see if we can remove > > > > mem_cgroup pointer > > > > > > > > > > You can't use flags field to store mem_cgroup_id while we use lock bit on it. > > > We have to store something more stable...as pfn or node-id or zone-id. > > > > > > It's very racy. > > > > > > > Yes, correct it is racy, there is no easy way from what I know we can write > > the upper 16 bits of the flag without affecting the lower 16 bits, if > > the 16 bits are changing. One of the techniques could be to have lock > > for the unsigned long word itself - but I don't know what performance > > overhead that would add. Having said that I would like to explore > > techniques that allow me to merge the two. > > > > to store pfn, we need to limit under 12bit. > I'll schedule my patch if dirty_ratio one goes. > cool! We'll redo the patch then and lets make this work. We'll need to see how many bits we need for section/node/zone to do pc_to_pfn() and pfn_to_page(). -- Three Cheers, Balbir