On 12/3/19 1:25 PM, Ajay Kaher wrote: > > > On 08/11/19, 3:08 PM, "Vlastimil Babka" <vbabka@xxxxxxx> wrote: > >> From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> >> >> commit 8fde12ca79aff9b5ba951fce1a2641901b8d8e64 upstream. >> >> [ 4.4 backport: there's get_page_foll(), so add try_get_page()-like checks >> in there, enabled by a new parameter, which is false where >> upstream patch doesn't replace get_page() with try_get_page() >> (the THP and hugetlb callers). > > Could we have try_get_page_foll(), as in: > https://lore.kernel.org/stable/1570581863-12090-3-git-send-email-akaher@xxxxxxxxxx/ > > + Code will be in sync as we have try_get_page() > + No need to add extra argument to try_get_page() > + No need to modify the callers of try_get_page() > >> In gup_pte_range(), we don't expect tail pages, so just check >> page ref count instead of try_get_compound_head() > > Technically it's fine. If you want to keep the code of stable versions in sync > with latest versions then this could be done in following ways (without any > modification in upstream patch for gup_pte_range()): > > Apply 7aef4172c7957d7e65fc172be4c99becaef855d4 before applying > 8fde12ca79aff9b5ba951fce1a2641901b8d8e64, as done here: > https://lore.kernel.org/stable/1570581863-12090-4-git-send-email-akaher@xxxxxxxxxx/ Yup, I have considered that, and deliberately didn't add that commit 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") as it's part of a large THP refcount rework. In 4.4 we don't expect to GUP tail pages so I wanted to keep it that way - minimally, the compound_head() operation is a unnecessary added cost, although it would also work.
