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authorDavid Hildenbrand <david@redhat.com>2024-04-18 18:18:34 +0300
committerAndrew Morton <akpm@linux-foundation.org>2024-05-06 03:53:42 +0300
commitd21f996b02a027f8915e493ee01370c4610ed2e2 (patch)
tree88bfda9cefa101afaae1fdf9a28eaac3551fc3f8
parent8430557fc584657559bfbd5150b6ae1bb90f35a0 (diff)
downloadlinux-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.c14
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)