Re: [PATCH] mm: align larger anonymous mappings on THP boundaries

[Yang Shi <shy828301@xxxxxxxxx>]

On Mon, Aug 8, 2022 at 1:47 PM Rik van Riel <riel@xxxxxxxxxxx> wrote:
>
> Align larger anonymous memory mappings on THP boundaries by
> going through thp_get_unmapped_area if THPs are enabled for
> the current process.
>
> With this patch, larger anonymous mappings are now THP aligned
> when checking in /proc/PID/maps, but only when THP is enabled
> for that process.
>
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
> ---
>  mm/mmap.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index c035020d0c89..3a9d19cec690 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2229,6 +2229,9 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
>                  */
>                 pgoff = 0;
>                 get_area = shmem_get_unmapped_area;
> +       } else if (test_bit(MMF_VM_HUGEPAGE, &current->mm->flags)) {

There is a kind of chicken & egg problem here, MMF_VM_HUGEPAGE is not
going to be set if there is no THP eligible vma even though THP is
enabled.

> +               /* Ensures that larger anonymous mappings are THP aligned. */
> +               get_area = thp_get_unmapped_area;
>         }
>
>         addr = get_area(file, addr, len, pgoff, flags);
> --
> 2.37.1
>
>