diff options
| author | David Hildenbrand <david@redhat.com> | 2024-04-18 18:18:34 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-05-06 03:53:42 +0300 |
| commit | d21f996b02a027f8915e493ee01370c4610ed2e2 (patch) | |
| tree | 88bfda9cefa101afaae1fdf9a28eaac3551fc3f8 | |
| parent | 8430557fc584657559bfbd5150b6ae1bb90f35a0 (diff) | |
| download | linux-d21f996b02a027f8915e493ee01370c4610ed2e2.tar.xz | |
mm/huge_memory: improve split_huge_page_to_list_to_order() return value documentation
The documentation is wrong and relying on it almost resulted in BUGs in
new callers: ever since fd4a7ac32918 ("mm: migrate: try again if THP split
is failed due to page refcnt") we return -EAGAIN on unexpected folio
references, not -EBUSY.
Let's fix that and also document which other return values we can
currently see and why they could happen.
[david@redhat.com: v2]
Link: https://lkml.kernel.org/r/20240422194217.442933-1-david@redhat.com
Link: https://lkml.kernel.org/r/20240418151834.216557-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/huge_memory.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 31b6bbffea52..eabf088cb444 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2956,7 +2956,7 @@ bool can_split_folio(struct folio *folio, int *pextra_pins) * * 3) The folio must not be pinned. Any unexpected folio references, including * GUP pins, will result in the folio not getting split; instead, the caller - * will receive an -EBUSY. + * will receive an -EAGAIN. * * 4) @new_order > 1, usually. Splitting to order-1 anonymous folios is not * supported for non-file-backed folios, because folio->_deferred_list, which @@ -2975,8 +2975,16 @@ bool can_split_folio(struct folio *folio, int *pextra_pins) * * Returns 0 if the huge page was split successfully. * - * Returns -EBUSY if @page's folio is pinned, or if the anon_vma disappeared - * from under us. + * Returns -EAGAIN if the folio has unexpected reference (e.g., GUP) or if + * the folio was concurrently removed from the page cache. + * + * Returns -EBUSY when trying to split the huge zeropage, if the folio is + * under writeback, if fs-specific folio metadata cannot currently be + * released, or if some unexpected race happened (e.g., anon VMA disappeared, + * truncation). + * + * Returns -EINVAL when trying to split to an order that is incompatible + * with the folio. Splitting to order 0 is compatible with all folios. */ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, unsigned int new_order) |