On Mon, 2018-08-27 at 18:04 +1000, Nicholas Piggin wrote:

quoted

Yes.. I see that. tlb_remove_check_page_size_change() really is a rather
ugly thing, it can cause loads of TLB flushes. Do you really _have_ to
do that? The way ARM and x86 work is that using INVLPG in a 4K stride is
still correct for huge pages, inefficient maybe, but so is flushing
every other page because 'sparse' transparant-huge-pages.

It could do that. It requires a tlbie that matches the page size,
so it means 3 sizes. I think possibly even that would be better
than current code, but we could do better if we had a few specific
fields in there.

More tlbies ? With the cost of the broadasts on the fabric ? I don't
think so.. or I'm not understanding your point...

Sadly our architecture requires a precise match between the page size
specified in the tlbie instruction and the entry in the TLB or it won't
be flushed.

Ben.