On 16 May 2025, at 8:39, David Hildenbrand wrote:
> Let's consistently return 0 if the operation was successful, and just
> detect ourselves whether splitting is required -- folio_test_large() is
> a cheap operation.
>
> Update the documentation.
>
> Should we simply always return -EAGAIN instead of 0, so we don't have
> to handle it in the caller? Not sure, staring at the documentation, this
> way looks a bit cleaner.
>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> arch/s390/kernel/uv.c | 22 ++++++++++++----------
> 1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index 2cc3b599c7fe3..f6ddb2b54032e 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -324,34 +324,36 @@ static int make_folio_secure(struct mm_struct *mm, struct folio *folio, struct u
> }
>
> /**
> - * s390_wiggle_split_folio() - try to drain extra references to a folio and optionally split.
> + * s390_wiggle_split_folio() - try to drain extra references to a folio and
> + * split the folio if it is large.
> * @mm: the mm containing the folio to work on
> * @folio: the folio
> - * @split: whether to split a large folio
> *
> * Context: Must be called while holding an extra reference to the folio;
> * the mm lock should not be held.
> - * Return: 0 if the folio was split successfully;
> - * -EAGAIN if the folio was not split successfully but another attempt
> - * can be made, or if @split was set to false;
> - * -EINVAL in case of other errors. See split_folio().
> + * Return: 0 if the operation was successful;
> + * -EAGAIN if splitting the large folio was not successful,
> + * but another attempt can be made;
> + * -EINVAL in case of other folio splitting errors. See split_folio().
> */
> -static int s390_wiggle_split_folio(struct mm_struct *mm, struct folio *folio, bool split)
> +static int s390_wiggle_split_folio(struct mm_struct *mm, struct folio *folio)
> {
> int rc;
>
> lockdep_assert_not_held(&mm->mmap_lock);
> folio_wait_writeback(folio);
> lru_add_drain_all();
> - if (split) {
> +
> + if (folio_test_large(folio)) {
> folio_lock(folio);
> rc = split_folio(folio);
> folio_unlock(folio);
>
> if (rc != -EBUSY)
> return rc;
> + return -EAGAIN;
> }
> - return -EAGAIN;
> + return 0;
> }
I can see how this function is written to service as two purposes,
trying to get rid of pcp ref of a folio and split a folio (to avoid
the extra pcp ref from failing split, lru_add_drain_all() is
called before split). Hope it will be refactored later.
>
> int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb)
> @@ -394,7 +396,7 @@ int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header
> mmap_read_unlock(mm);
>
> if (rc == -E2BIG || rc == -EBUSY) {
> - rc = s390_wiggle_split_folio(mm, folio, rc == -E2BIG);
> + rc = s390_wiggle_split_folio(mm, folio);
> if (!rc)
> rc = -EAGAIN;
> }
> --
> 2.49.0
The changes look good to me. Acked-by: Zi Yan <ziy@xxxxxxxxxx>
--
Best Regards,
Yan, Zi
