[PATCH v1 4/5] mm/rmap: introduce and use hugetlb_try_dup_anon_rmap()

David Hildenbrand
2023-11-28T14:52:35Z

hugetlb rmap handling differs quite a lot from "ordinary" rmap code, and
we already have dedicated functions for adding anon hugetlb folios and
removing hugetlb folios.

So let's introduce and use hugetlb_try_dup_anon_rmap() to make all
hugetlb handling use dedicated hugetlb_* rmap functions.

While this is a cleanup, this will also make it easier to change rmap
handling for partially-mappable folios.

Note that is_device_private_page() does not apply to hugetlb.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/mm.h | 12 +++++++++---
include/linux/rmap.h | 15 +++++++++++++++
mm/hugetlb.c | 3 +--
3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 418d26608ece..24c1c7c5a99c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1953,15 +1953,21 @@ static inline bool page_maybe_dma_pinned(struct page *page)
*
* The caller has to hold the PT lock and the vma->vm_mm->->write_protect_seq.
*/
-static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
- struct page *page)
+static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
+ struct folio *folio)
{
VM_BUG_ON(!(raw_read_seqcount(&vma->vm_mm->write_protect_seq) & 1));

if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))
return false;

- return page_maybe_dma_pinned(page);
+ return folio_maybe_dma_pinned(folio);
+}
+
+static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
+ struct page *page)
+{
+ return folio_needs_cow_for_dma(vma, page_folio(page));
}

/**
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 0a81e8420a96..8068c332e2ce 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -208,6 +208,21 @@ void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct *,
void hugetlb_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
unsigned long address);

+/* See page_try_dup_anon_rmap() */
+static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
+ struct vm_area_struct *vma)
+{
+ VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+
+ if (PageAnonExclusive(&folio->page)) {
+ if (unlikely(folio_needs_cow_for_dma(vma, folio)))
+ return -EBUSY;
+ ClearPageAnonExclusive(&folio->page);
+ }
+ atomic_inc(&folio->_entire_mapcount);
+ return 0;
+}
+
static inline void hugetlb_add_file_rmap(struct folio *folio)
{
VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 541a8f38cfdc..d927f8b2893c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5402,8 +5402,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
*/
if (!folio_test_anon(pte_folio)) {
hugetlb_add_file_rmap(pte_folio);
- } else if (page_try_dup_anon_rmap(&pte_folio->page,
- true, src_vma)) {
+ } else if (hugetlb_try_dup_anon_rmap(pte_folio, src_vma)) {
pte_t src_pte_old = entry;
struct folio *new_folio;

--
2.41.0