From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx202.postini.com [74.125.245.202]) by kanga.kvack.org (Postfix) with SMTP id CA1706B006C for ; Wed, 2 Jan 2013 13:17:31 -0500 (EST) Received: from /spool/local by e34.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 2 Jan 2013 11:17:30 -0700 Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id 4D3FC3E40045 for ; Wed, 2 Jan 2013 11:17:23 -0700 (MST) Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r02IHRq9331042 for ; Wed, 2 Jan 2013 11:17:27 -0700 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r02IHQ1n024639 for ; Wed, 2 Jan 2013 11:17:27 -0700 Message-ID: <50E479AD.9030502@linux.vnet.ibm.com> Date: Wed, 02 Jan 2013 10:17:17 -0800 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [PATCH 7/8] zswap: add to mm/ References: <<1355262966-15281-1-git-send-email-sjenning@linux.vnet.ibm.com>> <<1355262966-15281-8-git-send-email-sjenning@linux.vnet.ibm.com>> <0e91c1e5-7a62-4b89-9473-09fff384a334@default> <50E32255.60901@linux.vnet.ibm.com> <50E4588E.6080001@linux.vnet.ibm.com> <28a63847-7659-44c4-9c33-87f5d50b2ea0@default> In-Reply-To: <28a63847-7659-44c4-9c33-87f5d50b2ea0@default> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Magenheimer Cc: Seth Jennings , Greg Kroah-Hartman , Andrew Morton , Nitin Gupta , Minchan Kim , Konrad Wilk , Robert Jennings , Jenifer Hopper , Mel Gorman , Johannes Weiner , Rik van Riel , Larry Woodman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org On 01/02/2013 09:26 AM, Dan Magenheimer wrote: > However if one compares the total percentage > of RAM used for zpages by zswap vs the total percentage of RAM > used by slab, I suspect that the zswap number will dominate, > perhaps because zswap is storing primarily data and slab is > storing primarily metadata? That's *obviously* 100% dependent on how you configure zswap. But, that said, most of _my_ systems tend to sit with about 5% of memory in reclaimable slab which is certainly on par with how I'd expect to see zswap used. > I don't claim to be any kind of expert here, but I'd imagine > that MM doesn't try to manage the total amount of slab space > because slab is "a cost of doing business". However, for > in-kernel compression to be widely useful, IMHO it will be > critical for MM to somehow load balance between total pageframes > used for compressed pages vs total pageframes used for > normal pages, just as today it needs to balance between > active and inactive pages. The issue isn't about balancing. It's about reclaim where the VM only cares about whole pages. If our subsystem (zwhatever or slab) is only designed to reclaim _parts_ of pages, can we be successful in returning whole pages to the VM? The slab shrinkers only work on parts of pages (singular slab objects). Yet, it does appear that they function well enough when we try to reclaim from them. I've never seen a slab's sizes spiral out of control due to fragmentation. -- 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