[PATCH v1 02/39] mm/rmap: introduce and use hugetlb_remove_rmap()

David Hildenbrand
2023-12-11T15:57:08Z

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.

Let's introduce and use hugetlb_remove_rmap() and remove the hugetlb
code from page_remove_rmap(). This effectively removes one check on the
small-folio path as well.

Note: all possible candidates that need care are page_remove_rmap() that
pass compound=true.

Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/rmap.h | 5 +++++
mm/hugetlb.c | 4 ++--
mm/rmap.c | 17 ++++++++---------
3 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 0bfea866f39b..d85bd1d4de04 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -213,6 +213,11 @@ 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);

+static inline void hugetlb_remove_rmap(struct folio *folio)
+{
+ atomic_dec(&folio->_entire_mapcount);
+}
+
static inline void __page_dup_rmap(struct page *page, bool compound)
{
if (compound) {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 305f3ca1dee6..ef48ae673890 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5676,7 +5676,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
make_pte_marker(PTE_MARKER_UFFD_WP),
sz);
hugetlb_count_sub(pages_per_huge_page(h), mm);
- page_remove_rmap(page, vma, true);
+ hugetlb_remove_rmap(page_folio(page));

spin_unlock(ptl);
tlb_remove_page_size(tlb, page, huge_page_size(h));
@@ -5987,7 +5987,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,

/* Break COW or unshare */
huge_ptep_clear_flush(vma, haddr, ptep);
- page_remove_rmap(&old_folio->page, vma, true);
+ hugetlb_remove_rmap(old_folio);
hugetlb_add_new_anon_rmap(new_folio, vma, haddr);
if (huge_pte_uffd_wp(pte))
newpte = huge_pte_mkuffd_wp(newpte);
diff --git a/mm/rmap.c b/mm/rmap.c
index 80d42c31281a..4e60c1f38eaa 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1482,13 +1482,6 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,

VM_BUG_ON_PAGE(compound && !PageHead(page), page);

- /* Hugetlb pages are not counted in NR_*MAPPED */
- if (unlikely(folio_test_hugetlb(folio))) {
- /* hugetlb pages are always mapped with pmds */
- atomic_dec(&folio->_entire_mapcount);
- return;
- }
-
/* Is page being unmapped by PTE? Is this its last map to be removed? */
if (likely(!compound)) {
last = atomic_add_negative(-1, &page->_mapcount);
@@ -1846,7 +1839,10 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
dec_mm_counter(mm, mm_counter_file(&folio->page));
}
discard:
- page_remove_rmap(subpage, vma, folio_test_hugetlb(folio));
+ if (unlikely(folio_test_hugetlb(folio)))
+ hugetlb_remove_rmap(folio);
+ else
+ page_remove_rmap(subpage, vma, false);
if (vma->vm_flags & VM_LOCKED)
mlock_drain_local();
folio_put(folio);
@@ -2199,7 +2195,10 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
*/
}

- page_remove_rmap(subpage, vma, folio_test_hugetlb(folio));
+ if (unlikely(folio_test_hugetlb(folio)))
+ hugetlb_remove_rmap(folio);
+ else
+ page_remove_rmap(subpage, vma, false);
if (vma->vm_flags & VM_LOCKED)
mlock_drain_local();
folio_put(folio);
--
2.43.0