I'm sure there's some DMA going on there. The OS could simply keep a reserved zeroed out page and tell the DMA hardware to copy it wherever when it needs to zer

I'm sure there's some DMA going on there. The OS could simply keep a reserved zeroed out page and tell the DMA hardware to copy it wherever when it needs to zero out a page. I'd be rather surprised if tricks like that don't already happen. I'd be doubly surprised if modern DMA hardware doesn't support fancier tricks, if writing a repeated byte pattern is supported you wouldn't even need to reserve a whole page of zeroes, a single byte would do.