Re: [PATCH 2/3] mm/cow: optimise pte dirty/accessed bits handling in fork

From: Linus Torvalds
Date: Wed Aug 29 2018 - 19:15:52 EST

On Wed, Aug 29, 2018 at 4:12 PM Nicholas Piggin <npiggin@xxxxxxxxx> wrote:
> Dirty micro fault seems to be the big one for my Skylake, takes 300
> nanoseconds per access. Accessed takes about 100. (I think, have to
> go over my benchmark a bit more carefully and re-test).

Yeah, but they only happen for shared areas after fork, which sounds
like it shouldn't be a big deal in most cases.

And I'm not entirely objecting to your patch per se, I just would want
to keep the accessed bit changes separate from the dirty bit ones.

*If* somebody has bisectable issues with it (performance or not), it
will then be clearer what the exact issue is.