From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753169AbdLGL72 (ORCPT ); Thu, 7 Dec 2017 06:59:28 -0500 Received: from mga09.intel.com ([134.134.136.24]:22832 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753138AbdLGL71 (ORCPT ); Thu, 7 Dec 2017 06:59:27 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.45,372,1508828400"; d="scan'208";a="11369414" Message-ID: <5A292D94.5000700@intel.com> Date: Thu, 07 Dec 2017 20:01:24 +0800 From: Wei Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Tetsuo Handa , willy@infradead.org CC: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mst@redhat.com, mhocko@kernel.org, akpm@linux-foundation.org, mawilcox@microsoft.com, david@redhat.com, cornelia.huck@de.ibm.com, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu@aliyun.com, nilal@redhat.com, riel@redhat.com Subject: Re: [PATCH v18 05/10] xbitmap: add more operations References: <201711301934.CDC21800.FSLtJFFOOVQHMO@I-love.SAKURA.ne.jp> <5A210C96.8050208@intel.com> <201712012202.BDE13557.MJFQLtOOHVOFSF@I-love.SAKURA.ne.jp> <286AC319A985734F985F78AFA26841F739376DA1@shsmsx102.ccr.corp.intel.com> <20171201172519.GA27192@bombadil.infradead.org> <201712031050.IAC64520.QVLFFOOJOSFtHM@I-love.SAKURA.ne.jp> In-Reply-To: <201712031050.IAC64520.QVLFFOOJOSFtHM@I-love.SAKURA.ne.jp> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/03/2017 09:50 AM, Tetsuo Handa wrote: > Matthew Wilcox wrote: >> On Fri, Dec 01, 2017 at 03:09:08PM +0000, Wang, Wei W wrote: >>> On Friday, December 1, 2017 9:02 PM, Tetsuo Handa wrote: >>>> If start == end is legal, >>>> >>>> for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) { >>>> >>>> makes this loop do nothing because 10 < 10 is false. >>> How about "start <= end "? >> Don't ask Tetsuo for his opinion, write some userspace code that uses it. >> > Please be sure to prepare for "end == -1UL" case, for "start < end" will become > true when "start = (start | (IDA_BITMAP_BITS - 1)) + 1" made "start == 0" due to > overflow. I think there is one more corner case with this API: searching for bit "1" from [0, ULONG_MAX] while no bit is set in the range, there appear to be no possible value that we can return (returning "end + 1" will be "ULONG_MAX + 1", which is 0) I plan to make the "end" be exclusive of the searching, that is, [start, end), and return "end" if no such bit is found. For cases like [16, 16), returning 16 doesn't mean bit 16 is 1 or 0, it simply means there is no bits to search in the given range, since 16 is exclusive. Please let me know if you have a different thought. Best, Wei