mm/rmap: introduce and use hugetlb_remove_rmap()

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.

Add sanity checks that we end up with the right folios in the right
functions.

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

Link: https://lkml.kernel.org/r/20231220224504.646757-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 36096ba69bdcdbe919a76e5c59b3a28232fcd861..64ae6c4d72720b2be3c9857cf6db3cfa9081a248 100644 (file)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -211,6 +211,13 @@ 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)
+{
+       VM_WARN_ON_FOLIO(!folio_test_hugetlb(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 305f3ca1dee62acb043020a31df98ab495a192c7..ef48ae67389094be832b3ae8b9acd33b027869ef 100644 (file)
--- 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 @@ retry_avoidcopy:
 
                /* 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 9845499b22f8fafca0c3f37ec96ac94220fa49f8..261e1af0d254f2c834c300c79a6e599f6d29b720 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1480,15 +1480,9 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
        bool last;
        enum node_stat_item idx;
 
+       VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
        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 +1840,10 @@ 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 +2196,10 @@ 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);