Messages in this thread | | | Date | Thu, 1 Sep 2022 18:30:04 +0200 | From | David Hildenbrand <> | Subject | Re: [PATCH v1] mm/gup: adjust stale comment for RCU GUP-fast |
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On 01.09.22 18:12, Jason Gunthorpe wrote: > 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@linux.intel.com> >> Cc: Sasha Levin <sasha.levin@oracle.com> >> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> >> Cc: Vlastimil Babka <vbabka@suse.cz> >> Cc: Jerome Marchand <jmarchan@redhat.com> >> Cc: Andrea Arcangeli <aarcange@redhat.com> >> Cc: Hugh Dickins <hughd@google.com> >> Cc: Jason Gunthorpe <jgg@nvidia.com> >> Cc: John Hubbard <jhubbard@nvidia.com> >> Cc: Peter Xu <peterx@redhat.com> >> Cc: Yang Shi <shy828301@gmail.com> >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> 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.
Ah right. Will drop it as well -- thanks!
> > What is the current situation for THP splits anyhow? Is there are > comment in the fast pmd code explaining it?
Not aware of a comment, I think it just works naturally by always re-routing references taken on tail pages to the head page refcount.
Before that, we had "Tail page refcounting", which -- as I understand -- was a mess.
ddc58f27f9eee9117219936f77e90ad5b2e00e96 contains some comments.
> > But this seems OK too > > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > > Jason >
-- Thanks,
David / dhildenb
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