From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f199.google.com (mail-ot0-f199.google.com [74.125.82.199]) by kanga.kvack.org (Postfix) with ESMTP id C91C06B0038 for ; Fri, 1 Dec 2017 08:03:03 -0500 (EST) Received: by mail-ot0-f199.google.com with SMTP id i17so5103599otb.2 for ; Fri, 01 Dec 2017 05:03:03 -0800 (PST) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [2001:e42:101:1:202:181:97:72]) by mx.google.com with ESMTPS id y133si2087184oiy.238.2017.12.01.05.03.01 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 01 Dec 2017 05:03:02 -0800 (PST) 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> Date: Fri, 1 Dec 2017 22:02:01 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: 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 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org