Re: memfill

[James Bottomley <James.Bottomley@HansenPartnership.com>]

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