Le lundi 22 aoA>>t 2011 A  13:52 -0700, Andrew Morton a A(C)crit :

On Tue, 23 Aug 2011 01:29:07 +0900
Akinobu Mita [off-list ref] wrote:

quoted

memchr_inv() is mainly used to check whether the whole buffer is filled
with just a specified byte.

The function name and prototype are stolen from logfs and the
implementation is from SLUB.

...

+/**
+ * memchr_inv - Find a character in an area of memory.
+ * @s: The memory area
+ * @c: The byte to search for
+ * @n: The size of the area.

This text seems to be stolen from memchr().  I guess it's close enough.

quoted

+ * returns the address of the first character other than @c, or %NULL
+ * if the whole buffer contains just @c.
+ */
+void *memchr_inv(const void *start, int c, size_t bytes)
+{
+	u8 value = c;
+	u64 value64;
+	unsigned int words, prefix;
+
+	if (bytes <= 16)
+		return check_bytes8(start, value, bytes);
+
+	value64 = value | value << 8 | value << 16 | value << 24;
+	value64 = (value64 & 0xffffffff) | value64 << 32;
+	prefix = 8 - ((unsigned long)start) % 8;
+

<snip>

quoted

+	if (prefix) {
+		u8 *r = check_bytes8(start, value, prefix);
+		if (r)
+			return r;
+		start += prefix;
+		bytes -= prefix;
+	}

</snip>

Please note Andrew the previous code just make sure 'start' is aligned
on 8 bytes boundary. (It is suboptimal because if 'start' was already
aligned, we call the slow check_bytes(start, value, 8))

Code should probably do

prefix = (unsigned long)start % 8;
if (prefix) {
	prefix = 8 - prefix;
	r = check_bytes8(start, value, prefix);
	...

quoted

+
+	words = bytes / 8;
+
+	while (words) {
+		if (*(u64 *)start != value64)

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