Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966629Ab0GST7o (ORCPT ); Mon, 19 Jul 2010 15:59:44 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:39854 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966485Ab0GST7n convert rfc822-to-8bit (ORCPT ); Mon, 19 Jul 2010 15:59:43 -0400 MIME-Version: 1.0 Message-ID: <4f986c65-c17e-47d8-9c30-60cd17809cbb@default> Date: Mon, 19 Jul 2010 12:57:24 -0700 (PDT) From: Dan Magenheimer To: Nitin Gupta , Pekka Enberg , Hugh Dickins , Andrew Morton , Greg KH , Rik van Riel , Avi Kivity , Christoph Hellwig , Minchan Kim , Konrad Wilk Cc: linux-mm , linux-kernel Subject: RE: [PATCH 0/8] zcache: page cache compression support References: <1279283870-18549-1-git-send-email-ngupta@vflare.org> In-Reply-To: <1279283870-18549-1-git-send-email-ngupta@vflare.org> X-Priority: 3 X-Mailer: Oracle Beehive Extensions for Outlook 2.0.1.2.1.2 (406224) [OL 12.0.6535.5005] Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT X-Source-IP: acsmt354.oracle.com [141.146.40.154] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090205.4C44AE3C.0271:SCFMA4539814,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1139 Lines: 28 > We only keep pages that compress to PAGE_SIZE/2 or less. Compressed > chunks are > stored using xvmalloc memory allocator which is already being used by > zram > driver for the same purpose. Zero-filled pages are checked and no > memory is > allocated for them. I'm curious about this policy choice. I can see why one would want to ensure that the average page is compressed to less than PAGE_SIZE/2, and preferably PAGE_SIZE/2 minus the overhead of the data structures necessary to track the page. And I see that this makes no difference when the reclamation algorithm is random (as it is for now). But once there is some better reclamation logic, I'd hope that this compression factor restriction would be lifted and replaced with something much higher. IIRC, compression is much more expensive than decompression so there's no CPU-overhead argument here either, correct? Thanks, Dan -- 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/