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Date: Thu, 07 Dec 2017 20:01:24 +0800 From: Wei Wang <wei.w.wang@...el.com> To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, willy@...radead.org CC: virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org, qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com, mhocko@...nel.org, akpm@...ux-foundation.org, mawilcox@...rosoft.com, david@...hat.com, cornelia.huck@...ibm.com, mgorman@...hsingularity.net, aarcange@...hat.com, amit.shah@...hat.com, pbonzini@...hat.com, liliang.opensource@...il.com, yang.zhang.wz@...il.com, quan.xu@...yun.com, nilal@...hat.com, riel@...hat.com Subject: Re: [PATCH v18 05/10] xbitmap: add more operations 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
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