Date: 8 Feb 2015 13:48:23 -0500
Message-ID: <20150208184823.31349.qmail@ns.horizon.com>
From: "George Spelvin" <linux@horizon.com>
To: akpm@linux-foundation.org, chris@chris-wilson.co.uk, davem@davemloft.net,
        dborkman@redhat.com, hannes@stressinduktion.org,
        klimov.linux@gmail.com, laijs@cn.fujitsu.com, linux@horizon.com,
        msalter@redhat.com, takahiro.akashi@linaro.org, tgraf@suug.ch,
        valentinrothberg@gmail.com, yury.norov@gmail.com
Subject: Re: [PATCH v3 1/3] lib: find_*_bit reimplementation
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <1423404619-10653-2-git-send-email-yury.norov@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1858
Lines: 57

This basically has my Reviewed-by: (I'll send it in a few hours
when I have time to do a real final copy-editing), but a few minor
notes:

>+		/*
>+		 * This is an equvalent for:
>+		 *
>+		 * tmp = find_set ? addr[start / BITS_PER_LONG]
>+		 *	: ~addr[start / BITS_PER_LONG];
>+		 *
>+		 * but saves a branch condition.
>+		 *
>+		 * Thanks George Spelvin <linux@horizon.com> for idea.
>+		 */
>+		tmp = addr[start / BITS_PER_LONG] ^ mask;

1. There's no need for detailed credit for such a trivial and obvious
   thing.  If you want to comment it, describe the use of the parameter
   in the function header, e.g.

+/*
+ * "mask" is either 0 or ~0UL and XORed into each fetched word, to select between
+ * searching for one bits and zero bits.  If this function is inlined, GCC is
+ * smart enough to propagate the constant.
+ */

2. The variable might be more meaningfully named "xor" or "invert"; "mask"
   suggests something that is &-ed with a value.


> unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
> 				 unsigned long offset)
> {
>+	return _find_next_bit(addr, size, offset, ~0UL);	<---
> }

> unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
> {
>+	unsigned long idx;
> 
>+	for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
>+		if (addr[idx] != ULONG_MAX)			<---
>+			return min(idx * BITS_PER_LONG + ffz(addr[idx]), size);
> 	}
> 
>+	return size;
> }

3. Using two names (ULONG_MAX and ~0UL) for the same thing is a bit odd;
   you might want to be consistent.

I'll ack it either way; none of these are significant technical issues.
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