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

[Andi Kleen]

Srividya Desireddy <srividya.dr@xxxxxxxxxxx> writes:
>
> On a ARM Quad Core 32-bit device with 1.5GB RAM by launching and
> relaunching different applications, out of ~64000 pages stored in
> zswap, ~11000 pages were same-value filled pages (including zero-filled
> pages) and ~9000 pages were zero-filled pages.

What are the values for the non zero cases?

> +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?

Did you test the patch on a 64bit system?

Overall I would expect this extra pass to be fairly expensive. It may
be better to add some special check to the compressor, and let
it abort if it sees a string of same values, and only do the check
then.

-Andi