Re: memfill

James Bottomley
2017-02-07T19:08:00Z

On Mon, 2017-02-06 at 06:49 -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)

If we're going to do this, are you sure we wouldn't be wanting a string
fill instead of a memfill (because filling either by byte or long looks
a bit restrictive) assuming static strings that we can tell the compile
time size of, it would be easy for generic code to optimise.

James