On Fri, 4 Feb 2022 at 20:21, Matthew Wilcox (Oracle)
<willy@xxxxxxxxxxxxx> wrote:
>
> We still call try_grab_folio() once per PTE; a future patch could
> optimise to just adjust the reference count for each page within
> the folio.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
> ---
> mm/gup.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 00227b2cb1cf..44281350db1a 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2252,7 +2252,8 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
> ptem = ptep = pte_offset_map(&pmd, addr);
> do {
> pte_t pte = ptep_get_lockless(ptep);
> - struct page *head, *page;
> + struct page *page;
> + struct folio *folio;
>
> /*
> * Similar to the PMD case below, NUMA hinting must take slow
> @@ -2279,22 +2280,20 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
> VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
> page = pte_page(pte);
>
> - head = try_grab_compound_head(page, 1, flags);
> - if (!head)
> + folio = try_grab_folio(page, 1, flags);
> + if (!folio)
> goto pte_unmap;
>
> if (unlikely(page_is_secretmem(page))) {
> - put_compound_head(head, 1, flags);
> + gup_put_folio(folio, 1, flags);
> goto pte_unmap;
> }
>
> if (unlikely(pte_val(pte) != pte_val(*ptep))) {
> - put_compound_head(head, 1, flags);
> + gup_put_folio(folio, 1, flags);
> goto pte_unmap;
> }
>
> - VM_BUG_ON_PAGE(compound_head(page) != head, page);
> -
> /*
> * We need to make the page accessible if and only if we are
> * going to access its content (the FOLL_PIN case). Please
> @@ -2308,10 +2307,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
> goto pte_unmap;
> }
V. Minor/nit: Above the "goto pte_unmap;" is the code block;
if (flags & FOLL_PIN) {
ret = arch_make_page_accessible(page);
if (ret) {
unpin_user_page(page);
goto pte_unmap;
}
}
Other conditions which goto pte_unmap, after successful
try_grab_folio(), call gup_put_folio() (rather than
unpin_user_page()).
No change in functionality, but suggest calling gup_put_folio() here
too for consistency.
Cheers,
Mark
