On Tue, Mar 11, 2025 at 02:44:15PM +0100, Toke Høiland-Jørgensen wrote: > Pavel Begunkov <asml.silence@xxxxxxxxx> writes: > > If we're out of space in the page, why can't we use struct page * > > as indices into the xarray? Ala > > > > struct page *p = ...; > > xa_store(xarray, index=(unsigned long)p, p); > > > > Indices wouldn't be nicely packed, but it's still a map. Is there > > a problem with that I didn't consider? > > Huh. As I just replied to Yunsheng, I was under the impression that this > was not supported. But since you're now the second person to suggest > this, I looked again, and it looks like I was wrong. There does indeed > seem to be other places in the kernel that does this. > > As you say the indices won't be as densely packed, though. So I'm > wondering if using the bits in pp_magic would be better in any case to > get the better packing? I guess we can try benchmarking both approaches > and see if there's a measurable difference. This is an absolutely terrible idea, only proposed by those who have no understanding of how the XArray works. It could not be more wasteful.
