On 3/4/25 19:05, Matthew Wilcox wrote:
> On Tue, Mar 04, 2025 at 04:53:09PM +0000, Matthew Wilcox wrote:
>> Right, that's what happened in the block layer. We mark the bio with
>> BIO_PAGE_PINNED if the pincount needs to be dropped. As a transitional
>> period, we had BIO_PAGE_REFFED which indicated that the page refcount
>> needed to be dropped. Perhaps there's something similar that network
>> could be doing.
>
> Until that time ... how does this look as a quick hack to avoid
> reverting the slab change?
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index d6fed25243c3..ca08a923ac6d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1520,7 +1520,10 @@ static inline void folio_get(struct folio *folio)
>
> static inline void get_page(struct page *page)
> {
> - folio_get(page_folio(page));
> + struct folio *folio = page_folio(page);
> + if (WARN_ON_ONCE(folio_test_slab(folio)))
> + return;
> + folio_get(folio);
Maybe we could do just VM_WARN_ON_ONCE if we fix the known offender fully.
> }
>
> static inline __must_check bool try_get_page(struct page *page)
> @@ -1614,6 +1617,8 @@ static inline void put_page(struct page *page)
> {
> struct folio *folio = page_folio(page);
>
> + if (folio_test_slab(folio))
> + return;
And that means knowing where the put_page() side is and skipping it for slab
pages like for the get_page() side below. Hannes could you apply this patch
but also with WARN_ON_ONCE here in put_page()? And tell us where the
put_page() splats. Thanks!
> folio_put(folio);
> }
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 65f550cb5081..8c7fdb7d8c8f 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1190,8 +1190,12 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
> if (!n)
> return -ENOMEM;
> p = *pages;
> - for (int k = 0; k < n; k++)
> - get_page(p[k] = page + k);
> + for (int k = 0; k < n; k++) {
> + struct folio *folio = page_folio(page);
> + p[k] = page + k;
> + if (!folio_test_slab(folio))
> + folio_get(folio);
> + }
> maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start);
> i->count -= maxsize;
> i->iov_offset += maxsize;
