Re: memfill

Minchan Kim
2017-02-07T05:00:05Z

Hi Matthew,

On Mon, Feb 06, 2017 at 06:49:02AM -0800, 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).

Thanks for suggestion, Matthew!

However, I want to mention zram's performance wouldn't be sensitive
for that function because non-zero memfill would be rare.