From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39980) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eQ9S1-0001Mf-RO for qemu-devel@nongnu.org; Sat, 16 Dec 2017 05:12:15 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eQ9Rx-0004KM-Ra for qemu-devel@nongnu.org; Sat, 16 Dec 2017 05:12:13 -0500 Received: from mga07.intel.com ([134.134.136.100]:16737) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eQ9Rx-0004IU-HQ for qemu-devel@nongnu.org; Sat, 16 Dec 2017 05:12:09 -0500 Message-ID: <5A34F1F4.6010900@intel.com> Date: Sat, 16 Dec 2017 18:14:12 +0800 From: Wei Wang MIME-Version: 1.0 References: <1513079759-14169-4-git-send-email-wei.w.wang@intel.com> <201712122220.IFH05261.LtJOFFSFHVMQOO@I-love.SAKURA.ne.jp> <5A311C5E.7000304@intel.com> <201712132316.EJJ57332.MFOSJHOFFVLtQO@I-love.SAKURA.ne.jp> <5A31F445.6070504@intel.com> <201712150129.BFC35949.FFtFOLSOJOQHVM@I-love.SAKURA.ne.jp> In-Reply-To: <201712150129.BFC35949.FFtFOLSOJOQHVM@I-love.SAKURA.ne.jp> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Tetsuo Handa 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, willy@infradead.org, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu@aliyun.com, nilal@redhat.com, riel@redhat.com On 12/15/2017 12:29 AM, Tetsuo Handa wrote: > Wei Wang wrote: >> I used the example of xb_clear_bit_range(), and xb_find_next_bit() is >> the same fundamentally. Please let me know if anywhere still looks fuzzy. > I don't think it is the same for xb_find_next_bit() with set == 0. > > + if (radix_tree_exception(bmap)) { > + unsigned long tmp = (unsigned long)bmap; > + unsigned long ebit = bit + 2; > + > + if (ebit >= BITS_PER_LONG) > + continue; > + if (set) > + ret = find_next_bit(&tmp, BITS_PER_LONG, ebit); > + else > + ret = find_next_zero_bit(&tmp, BITS_PER_LONG, > + ebit); > + if (ret < BITS_PER_LONG) > + return ret - 2 + IDA_BITMAP_BITS * index; > > What I'm saying is that find_next_zero_bit() will not be called if you do > "if (ebit >= BITS_PER_LONG) continue;" before calling find_next_zero_bit(). > > When scanning "0000000000000000000000000000000000000000000000000000000000000001", > "bit < BITS_PER_LONG - 2" case finds "0" in this word but > "bit >= BITS_PER_LONG - 2" case finds "0" in next word or segment. > > I can't understand why this is correct behavior. It is too much puzzling. > OK, I'll post out a version without the exceptional path. Best, Wei