On 27/06/2023 02:55, Yu Zhao wrote:

On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts [off-list ref] wrote:

quoted

In preparation for extending vma_alloc_zeroed_movable_folio() to
allocate a arbitrary order folio, expose clear_huge_page()
unconditionally, so that it can be used to zero the allocated folio in
the generic implementation of vma_alloc_zeroed_movable_folio().

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 include/linux/mm.h | 3 ++-
 mm/memory.c        | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7f1741bd870a..7e3bf45e6491 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -3684,10 +3684,11 @@ enum mf_action_page_type {
  */
 extern const struct attribute_group memory_failure_attr_group;

-#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
 extern void clear_huge_page(struct page *page,
                            unsigned long addr_hint,
                            unsigned int pages_per_huge_page);
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)

We might not want to depend on THP eventually. Right now, we still
have to, unless splitting is optional, which seems to contradict
06/10. (deferred_split_folio()  is a nop without THP.)

Yes, I agree - for large anon folios to work, we depend on THP. But I don't
think that helps us here.

In the next patch, I give vma_alloc_zeroed_movable_folio() an extra `order`
parameter. So the generic/default version of the function now needs a way to
clear a compound page.

I guess I could do something like:

 static inline
 struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
				   unsigned long vaddr, gfp_t gfp, int order)
 {
 	struct folio *folio;

	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp,
					order, vma, vaddr, false);
 	if (folio) {
#ifdef CONFIG_LARGE_FOLIO
		clear_huge_page(&folio->page, vaddr, 1U << order);
#else
		BUG_ON(order != 0);
		clear_user_highpage(&folio->page, vaddr);
#endif
	}

 	return folio;
 }

But that's pretty messy and there's no reason why other users might come along
that pass order != 0 and will be surprised by the BUG_ON.

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