[PATCH v1 05/39] mm/rmap: introduce and use hugetlb_try_share_anon_rmap()

David Hildenbrand
2023-12-11T15:57:23Z

hugetlb rmap handling differs quite a lot from "ordinary" rmap code.
For example, hugetlb currently only supports entire mappings, and treats
any mapping as mapped using a single "logical PTE". Let's move it out
of the way so we can overhaul our "ordinary" rmap.
implementation/interface.

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

Note that try_to_unmap_one() does not need care. Easy to spot because
among all that nasty hugetlb special-casing in that function, we're not
using set_huge_pte_at() on the anon path -- well, and that code assumes
that we would want to swapout.

Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/rmap.h | 23 +++++++++++++++++++++++
mm/rmap.c | 15 ++++++++++-----
2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index ca42b3db5688..4c0650e9f6db 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -228,6 +228,29 @@ static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
return 0;
}

+/* See page_try_share_anon_rmap() */
+static inline int hugetlb_try_share_anon_rmap(struct folio *folio)
+{
+ VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+ VM_WARN_ON_FOLIO(!PageAnonExclusive(&folio->page), folio);
+
+ /* Paired with the memory barrier in try_grab_folio(). */
+ if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
+ smp_mb();
+
+ if (unlikely(folio_maybe_dma_pinned(folio)))
+ return -EBUSY;
+ ClearPageAnonExclusive(&folio->page);
+
+ /*
+ * This is conceptually a smp_wmb() paired with the smp_rmb() in
+ * gup_must_unshare().
+ */
+ if (IS_ENABLED(CONFIG_HAVE_FAST_GUP))
+ smp_mb__after_atomic();
+ 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/rmap.c b/mm/rmap.c
index 4e60c1f38eaa..e210ac1b73de 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2147,13 +2147,18 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
!anon_exclusive, subpage);

/* See page_try_share_anon_rmap(): clear PTE first. */
- if (anon_exclusive &&
- page_try_share_anon_rmap(subpage)) {
- if (folio_test_hugetlb(folio))
+ if (folio_test_hugetlb(folio)) {
+ if (anon_exclusive &&
+ hugetlb_try_share_anon_rmap(folio)) {
set_huge_pte_at(mm, address, pvmw.pte,
pteval, hsz);
- else
- set_pte_at(mm, address, pvmw.pte, pteval);
+ ret = false;
+ page_vma_mapped_walk_done(&pvmw);
+ break;
+ }
+ } else if (anon_exclusive &&
+ page_try_share_anon_rmap(subpage)) {
+ set_pte_at(mm, address, pvmw.pte, pteval);
ret = false;
page_vma_mapped_walk_done(&pvmw);
break;
--
2.43.0