From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752617AbdLANCF (ORCPT ); Fri, 1 Dec 2017 08:02:05 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:30268 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751986AbdLANCD (ORCPT ); Fri, 1 Dec 2017 08:02:03 -0500 To: wei.w.wang@intel.com 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 Subject: Re: [PATCH v18 05/10] xbitmap: add more operations From: Tetsuo Handa References: <1511963726-34070-1-git-send-email-wei.w.wang@intel.com> <1511963726-34070-6-git-send-email-wei.w.wang@intel.com> <201711301934.CDC21800.FSLtJFFOOVQHMO@I-love.SAKURA.ne.jp> <5A210C96.8050208@intel.com> In-Reply-To: <5A210C96.8050208@intel.com> Message-Id: <201712012202.BDE13557.MJFQLtOOHVOFSF@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Fri, 1 Dec 2017 22:02:01 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Wei Wang wrote: > On 11/30/2017 06:34 PM, Tetsuo Handa wrote: > > Wei Wang wrote: > >> + * @start: the start of the bit range, inclusive > >> + * @end: the end of the bit range, inclusive > >> + * > >> + * This function is used to clear a bit in the xbitmap. If all the bits of the > >> + * bitmap are 0, the bitmap will be freed. > >> + */ > >> +void xb_clear_bit_range(struct xb *xb, unsigned long start, unsigned long end) > >> +{ > >> + struct radix_tree_root *root = &xb->xbrt; > >> + struct radix_tree_node *node; > >> + void **slot; > >> + struct ida_bitmap *bitmap; > >> + unsigned int nbits; > >> + > >> + for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) { > >> + unsigned long index = start / IDA_BITMAP_BITS; > >> + unsigned long bit = start % IDA_BITMAP_BITS; > >> + > >> + bitmap = __radix_tree_lookup(root, index, &node, &slot); > >> + if (radix_tree_exception(bitmap)) { > >> + unsigned long ebit = bit + 2; > >> + unsigned long tmp = (unsigned long)bitmap; > >> + > >> + nbits = min(end - start + 1, BITS_PER_LONG - ebit); > > "nbits = min(end - start + 1," seems to expect that start == end is legal > > for clearing only 1 bit. But this function is no-op if start == end. > > Please clarify what "inclusive" intended. > > If xb_clear_bit_range(xb,10,10), then it is effectively the same as > xb_clear_bit(10). Why would it be illegal? > > "@start inclusive" means that the @start will also be included to be > cleared. 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. > > > > >> +static inline __always_inline void bitmap_clear(unsigned long *map, > >> + unsigned int start, > >> + unsigned int nbits) > >> +{ > >> + if (__builtin_constant_p(nbits) && nbits == 1) > >> + __clear_bit(start, map); > >> + else if (__builtin_constant_p(start & 7) && IS_ALIGNED(start, 8) && > >> + __builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8)) > > It looks strange to apply __builtin_constant_p test to variables after "& 7". > > > > I think this is normal - if the variables are known at compile time, the > calculation will be done at compile time (termed constant folding). I think that + else if (__builtin_constant_p(start) && IS_ALIGNED(start, 8) && + __builtin_constant_p(nbits) && IS_ALIGNED(nbits, 8)) is more readable.