Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757759AbaKUGsV (ORCPT ); Fri, 21 Nov 2014 01:48:21 -0500 Received: from mail-pa0-f43.google.com ([209.85.220.43]:49136 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751183AbaKUGsT (ORCPT ); Fri, 21 Nov 2014 01:48:19 -0500 Date: Fri, 21 Nov 2014 06:48:49 +0000 From: Minchan Kim To: Ganesh Mahendran Cc: Nitin Gupta , Joonsoo Kim , Linux-MM , linux-kernel Subject: Re: [RFC PATCH] mm/zsmalloc: remove unnecessary check Message-ID: <20141121064849.GA17181@gmail.com> References: <1416489716-9967-1-git-send-email-opensource.ganesh@gmail.com> <20141121035442.GB10123@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 On Fri, Nov 21, 2014 at 01:33:26PM +0800, Ganesh Mahendran wrote: > Hello > > 2014-11-21 11:54 GMT+08:00 Minchan Kim : > > On Thu, Nov 20, 2014 at 09:21:56PM +0800, Mahendran Ganesh wrote: > >> ZS_SIZE_CLASSES is calc by: > >> ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1) > >> > >> So when i is in [0, ZS_SIZE_CLASSES - 1), the size: > >> size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA > >> will not be greater than ZS_MAX_ALLOC_SIZE > >> > >> This patch removes the unnecessary check. > > > > It depends on ZS_MIN_ALLOC_SIZE. > > For example, we would change min to 8 but MAX is still 4096. > > ZS_SIZE_CLASSES is (4096 - 8) / 16 + 1 = 256 so 8 + 255 * 16 = 4088, > > which exceeds the max. > Here, 4088 is less than MAX(4096). > > ZS_SIZE_CLASSES = (MAX - MIN) / Delta + 1 > So, I think the value of > MIN + (ZS_SIZE_CLASSES - 1) * Delta = > MIN + ((MAX - MIN) / Delta) * Delta = > MAX > will not exceed the MAX You're right. It was complext math for me. I should go back to elementary school. Thanks! Acked-by: Minchan Kim -- 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/