Re: memfill

[zhouxianrong]

On 2017/2/6 22:49, Matthew Wilcox wrote:

[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).

good idea, i hope kernel could support family functions like memfill/memset_long
in lib. but this is beyond zram scope.

.