From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752054AbdK3KeK (ORCPT ); Thu, 30 Nov 2017 05:34:10 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:43638 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbdK3KeJ (ORCPT ); Thu, 30 Nov 2017 05:34:09 -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> In-Reply-To: <1511963726-34070-6-git-send-email-wei.w.wang@intel.com> Message-Id: <201711301934.CDC21800.FSLtJFFOOVQHMO@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Thu, 30 Nov 2017 19:34:10 +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: > /** > + * xb_clear_bit - clear a range of bits in the xbitmap Name mismatch. > + * @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 (ebit >= BITS_PER_LONG) > + continue; (I don't understand how radix tree works, but generally this patchset looks fuzzy to me about boundary cases. Thus, I want to confirm that this is not an overlook.) Why is making "ebit >= BITS_PER_LONG" (e.g. start == 62) case a no-op correct? Aren't there bits which should have been cleared in this case? > + bitmap_clear(&tmp, ebit, nbits); > + if (tmp == RADIX_TREE_EXCEPTIONAL_ENTRY) > + __radix_tree_delete(root, node, slot); > + else > + rcu_assign_pointer(*slot, (void *)tmp); > + } else if (bitmap) { > + nbits = min(end - start + 1, IDA_BITMAP_BITS - bit); > + > + if (nbits != IDA_BITMAP_BITS) > + bitmap_clear(bitmap->bitmap, bit, nbits); > + > + if (nbits == IDA_BITMAP_BITS || > + bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) { > + kfree(bitmap); > + __radix_tree_delete(root, node, slot); > + } > + } > + } > +} > +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". > + memset((char *)map + start / 8, 0, nbits / 8); > + else > + __bitmap_clear(map, start, nbits); > +} > +