Re: [PATCH v1] mm/gup: adjust stale comment for RCU GUP-fast

[Peter Xu]

On Thu, Sep 01, 2022 at 10:50:48AM -0700, Yang Shi wrote:
> Yeah, because THP collapse does copy the data before clearing pte. If
> we want to remove pmdp_collapse_flush() by just clearing pmd, we
> should clear *AND* flush pte before copying the data IIRC.

Yes tlb flush is still needed.  IIUC the generic pmdp_collapse_flush() will
still be working (with the pte level flushing there) but it should just
start to work for all archs, so potentially we could drop the arch-specific
pmdp_collapse_flush()s, mostly the ppc impl.

This also reminded me that the s390 version of pmdp_collapse_flush() is a
bit weird, since it doesn't even have the tlb flush there.  I feel like
it's broken but I can't really tell whether something I've overlooked.
Worth an eye on.

-- 
Peter Xu