Re: [PATCH] zswap: Same-filled pages handling

[Matthew Wilcox]

On Wed, Oct 18, 2017 at 01:43:10PM -0700, Andi Kleen wrote:
> > +static int zswap_is_page_same_filled(void *ptr, unsigned long *value)
> > +{
> > +	unsigned int pos;
> > +	unsigned long *page;
> > +
> > +	page = (unsigned long *)ptr;
> > +	for (pos = 1; pos < PAGE_SIZE / sizeof(*page); pos++) {
> > +		if (page[pos] != page[0])
> > +			return 0;
> > +	}
> 
> So on 32bit it checks for 32bit repeating values and on 64bit
> for 64bit repeating values. Does that make sense?

Yes.  Every 64-bit repeating pattern is also a 32-bit repeating pattern.
Supporting a 64-bit pattern on a 32-bit kernel is painful, but it makes
no sense to *not* support a 64-bit pattern on a 64-bit kernel.  This is
the same approach used in zram, fwiw.