memfill

Matthew Wilcox
2017-02-06T14:49:13Z

[adding linux-arch to see if anyone there wants to do an optimised
version of memfill for their CPU]

On Mon, Feb 06, 2017 at 12:16:44AM +0900, Minchan Kim wrote:
> +static inline void zram_fill_page(char *ptr, unsigned long len,
> + unsigned long value)
> +{
> + int i;
> + unsigned long *page = (unsigned long *)ptr;
> +
> + WARN_ON_ONCE(!IS_ALIGNED(len, sizeof(unsigned long)));
> +
> + if (likely(value == 0)) {
> + memset(ptr, 0, len);
> + } else {
> + for (i = 0; i < len / sizeof(*page); i++)
> + page[i] = value;
> + }
> +}

I would suggest:

#ifndef __HAVE_ARCH_MEMFILL
/**
* memfill - Fill a region of memory with the given value
* @s: Pointer to the start of the region.
* @v: The word to fill the region with.
* @n: The size of the region.
*
* Differs from memset() in that it fills with an unsigned long instead of
* a byte. The pointer and the size must be aligned to unsigned long.
*/
void memfill(unsigned long *s, unsigned long v, size_t n)
{
WARN_ON_ONCE(!IS_ALIGNED(n, sizeof(v)));

if (likely(v == 0)) {
memset(s, 0, n);
} else {
while (n) {
*s++ = v;
n -= sizeof(v);
}
}
}
EXPORT_SYMBOL(memfill);
#endif

(I would also suggest this move to lib/string.c and architectures be
given the opportunity to provide an optimised version of memfill).