Re: [PATCH] ovl: implement ->get_unmapped_area()

[Miklos Szeredi]

On Fri, 28 Aug 2026 at 14:41, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:

> No, not at all.  All this patch needs to be is:
>
> +++ b/fs/overlayfs/file.c
> @@ -657,6 +657,7 @@ const struct file_operations ovl_file_operations = {
>         .fallocate      = ovl_fallocate,
>         .fadvise        = ovl_fadvise,
>         .flush          = ovl_flush,
> +       .get_unmapped_area = thp_get_unmapped_area,
>         .splice_read    = ovl_splice_read,
>         .splice_write   = ovl_splice_write,
>
>
> All this "oh we have to call the underlying filesystem's
> get_unmapepd_area" betrays a lack of understanding of the problem.
>
> And Lorenzo suggested this in the linked thread:
>
> https://lore.kernel.org/linux-unionfs/69b72e3d-b101-4641-9ce5-51346c93a98d@lucifer.local/

There seems to be a logical fallacy in saying thp_get_unmapepd_area is
the most suitable value, yet not making it the default for all
filesystems.

Saying this without any understanding of the subtle difference between
setting .get_unmapepd_area to NULL and to thp_get_unmapepd_area.   All
I can see that the difference is indeed subtle.

Can you please explain?

Thanks,
Miklos