Re: [PATCH v4 5/5] hugetlb: Do early cow when page pinned on src mm

[Jason Gunthorpe]

On Mon, Feb 08, 2021 at 10:02:29PM -0500, Peter Xu wrote:
> This is the last missing piece of the COW-during-fork effort when there're
> pinned pages found.  One can reference 70e806e4e645 ("mm: Do early cow for
> pinned pages during fork() for ptes", 2020-09-27) for more information, since
> we do similar things here rather than pte this time, but just for hugetlb.
> 
> Note that after Jason's recent work on 57efa1fe5957 ("mm/gup: prevent gup_fast
> from racing with COW during fork", 2020-12-15) which is safer and easier to
> understand, we're safe now within the whole copy_page_range() against gup-fast,
> we don't need the wr-protect trick that proposed in 70e806e4e645 anymore.
> 
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
>  mm/hugetlb.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 62 insertions(+), 4 deletions(-)

Didn't check every hugetlbfs detail, but looks reasonable

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason