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

[Jason Gunthorpe]

On Thu, Sep 01, 2022 at 09:21:19AM +0200, David Hildenbrand wrote:
> commit 4b471e8898c3 ("mm, thp: remove infrastructure for handling splitting
> PMDs") didn't remove all details about the THP split requirements for
> RCU GUP-fast.
> 
> IPI broeadcasts on THP split are no longer required.
> 
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Jerome Marchand <jmarchan@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Peter Xu <peterx@xxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  mm/gup.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)

The comment a bit above seems to need touching to:

 * protected from page table pages being freed from under it, and should
 * block any THP splits.

What is the current situation for THP splits anyhow? Is there are
comment in the fast pmd code explaining it?

But this seems OK too

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason