Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935039Ab3E2Tuw (ORCPT ); Wed, 29 May 2013 15:50:52 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:35839 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759629Ab3E2Tuq (ORCPT ); Wed, 29 May 2013 15:50:46 -0400 Date: Wed, 29 May 2013 14:50:27 -0500 From: Seth Jennings To: Andrew Morton Cc: Greg Kroah-Hartman , Nitin Gupta , Minchan Kim , Konrad Rzeszutek Wilk , Dan Magenheimer , Robert Jennings , Jenifer Hopper , Mel Gorman , Johannes Weiner , Rik van Riel , Larry Woodman , Benjamin Herrenschmidt , Dave Hansen , Joe Perches , Joonsoo Kim , Cody P Schafer , Hugh Dickens , Paul Mackerras , Heesub Shin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org Subject: Re: [PATCHv12 3/4] zswap: add to mm/ Message-ID: <20130529195027.GC428@cerebellum> References: <1369067168-12291-1-git-send-email-sjenning@linux.vnet.ibm.com> <1369067168-12291-4-git-send-email-sjenning@linux.vnet.ibm.com> <20130528145918.acbd84df00313e527cf04d1b@linux-foundation.org> <20130529145720.GA428@cerebellum> <20130529112929.24005ae9cf1d9d636b2ea42f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130529112929.24005ae9cf1d9d636b2ea42f@linux-foundation.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13052919-5806-0000-0000-000021671312 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2062 Lines: 44 On Wed, May 29, 2013 at 11:29:29AM -0700, Andrew Morton wrote: > On Wed, 29 May 2013 09:57:20 -0500 Seth Jennings wrote: > > > > > +/********************************* > > > > +* helpers > > > > +**********************************/ > > > > +static inline bool zswap_is_full(void) > > > > +{ > > > > + return (totalram_pages * zswap_max_pool_percent / 100 < > > > > + zswap_pool_pages); > > > > +} > > > > > > We have had issues in the past where percentage-based tunables were too > > > coarse on very large machines. For example, a terabyte machine where 0 > > > bytes is too small and 10GB is too large. > > > > Yes, this is known limitation of the code right now and it is a high priority > > to come up with something better. It isn't clear what dynamic sizing policy > > should be used so, until such time as that policy can be determined, this is a > > simple stop-gap that works well enough for simple setups. > > It's a module parameter and hence is part of the userspace interface. > It's undesirable that the interface be changed, and it would be rather > dumb to merge it as-is when we *know* that it will be changed. > > I don't think we can remove the parameter altogether (or can we?), so I > suggest we finalise it ASAP. Perhaps rename it to > zswap_max_pool_ratio, with a range 1..999999. Better ideas needed :( zswap_max_pool_ratio is fine with me. I'm not entirely clear on the change though. Would that just be a name change or a change in meaning? Also, we can keep the tunable as I imagine there will always be some use for a manual override of the (future) dynamic policy. When the dynamic policy is available, we can just say that zswap_max_pool_ratio = 0 means "use dynamic policy" and change the default to 0. Does that sounds reasonable? Seth -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/