On 3/13/24 2:20 AM, David Hildenbrand wrote: ...
The description is wrong. Whoever calls split_huge_page_to_list() must hold a folio reference. That folio reference will be transferred to @page (not the head page) once split. So @page can be used by the caller after the split succeeded.
David and all, does this updated draft comment look accurate? /* * This function splits a huge page into normal pages. @page can point to any * subpage of the huge page to split. The split operation does not change the * position of @page. * * Prerequisites: * * 1) The caller must hold a reference on the @page's owning folio, also known as * the huge page. * * 2) The huge page must be locked. * * 3) The folio must not be pinned. Pinned folios will not be split; instead, * the caller will receive an -EBUSY. * * After splitting, the folio's refcount is transfered to @page (not the head * page, unless @page is actually the head page). The other subpages may be * freed if they are not mapped. * * If @list is null, tail pages will be added to LRU list, otherwise, to @list. * * Both head page and tail pages will inherit mapping, flags, and so on from the * hugepage. * * Returns 0 if the hugepage was split successfully. * * Returns -EBUSY if @page's folio is pinned, or if the anon_vma disappeared * from under us. */ int split_huge_page_to_list(struct page *page, struct list_head *list)
thanks, -- John Hubbard NVIDIA
