From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id E44A09000BD for ; Thu, 15 Sep 2011 13:30:25 -0400 (EDT) MIME-Version: 1.0 Message-ID: <075c4e4c-a22d-47d1-ae98-31839df6e722@default> Date: Thu, 15 Sep 2011 10:29:51 -0700 (PDT) From: Dan Magenheimer Subject: RE: [PATCH v2 0/3] staging: zcache: xcfmalloc support References: <1315404547-20075-1-git-send-email-sjenning@linux.vnet.ibm.com> <20110909203447.GB19127@kroah.com> <4E6ACE5B.9040401@vflare.org> <4E6E18C6.8080900@linux.vnet.ibm.com> <4E6EB802.4070109@vflare.org> <4E6F7DA7.9000706@linux.vnet.ibm.com> <4E6FC8A1.8070902@vflare.org 4E72284B.2040907@linux.vnet.ibm.com> In-Reply-To: <4E72284B.2040907@linux.vnet.ibm.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Seth Jennings , Nitin Gupta Cc: Greg KH , gregkh@suse.de, devel@driverdev.osuosl.org, cascardo@holoscopio.com, linux-kernel@vger.kernel.org, dave@linux.vnet.ibm.com, linux-mm@kvack.org, brking@linux.vnet.ibm.com, rcj@linux.vnet.ibm.com > From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com] > Subject: Re: [PATCH v2 0/3] staging: zcache: xcfmalloc support >=20 > Hey Nitin, >=20 > So this is how I see things... >=20 > Right now xvmalloc is broken for zcache's application because > of its huge fragmentation for half the valid allocation sizes > (> PAGE_SIZE/2). Um, I have to disagree here. It is broken for zcache for SOME set of workloads/data, where the AVERAGE compression is poor (> PAGE_SIZE/2). =20 > My xcfmalloc patches are _a_ solution that is ready now. Sure, > it doesn't so compaction yet, and it has some metadata overhead. > So it's not "ideal" (if there is such I thing). But it does fix > the brokenness of xvmalloc for zcache's application. But at what cost? As Dave Hansen pointed out, we still do not have a comprehensive worst-case performance analysis for xcfmalloc. Without that (and without an analysis over a very large set of workloads), it is difficult to characterize one as "better" than the other. > So I see two ways going forward: >=20 > 1) We review and integrate xcfmalloc now. Then, when you are > done with your allocator, we can run them side by side and see > which is better by numbers. If yours is better, you'll get no > argument from me and we can replace xcfmalloc with yours. >=20 > 2) We can agree on a date (sooner rather than later) by which your > allocator will be completed. At that time we can compare them and > integrate the best one by the numbers. >=20 > Which would you like to do? Seth, I am still not clear why it is not possible to support either allocation algorithm, selectable at runtime. Or even dynamically... use xvmalloc to store well-compressible pages and xcfmalloc for poorly-compressible pages. I understand it might require some additional coding, perhaps even an ugly hack or two, but it seems possible. Dan -- 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