mm/thp: carry over dirty bit when thp splits on pmd

Carry over the dirty bit from pmd to pte when a huge pmd splits.  It
shouldn't be a correctness issue since when pmd_dirty() we'll have the
page marked dirty anyway, however having dirty bit carried over helps the
next initial writes of split ptes on some archs like x86.

Link: https://lkml.kernel.org/r/20220811161331.37055-5-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Huang Ying <ying.huang@intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andi Kleen <andi.kleen@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7bf2299cb24bd37d17d1bb5d4f0d5cabd0f19c44..b4666774abf08da3289eb3c7df39f8abfce4c278 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2037,7 +2037,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
        pgtable_t pgtable;
        pmd_t old_pmd, _pmd;
        bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
-       bool anon_exclusive = false;
+       bool anon_exclusive = false, dirty = false;
        unsigned long addr;
        int i;
 
@@ -2126,8 +2126,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
                uffd_wp = pmd_swp_uffd_wp(old_pmd);
        } else {
                page = pmd_page(old_pmd);
-               if (pmd_dirty(old_pmd))
+               if (pmd_dirty(old_pmd)) {
+                       dirty = true;
                        SetPageDirty(page);
+               }
                write = pmd_write(old_pmd);
                young = pmd_young(old_pmd);
                soft_dirty = pmd_soft_dirty(old_pmd);
@@ -2195,6 +2197,9 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
                                entry = pte_wrprotect(entry);
                        if (!young)
                                entry = pte_mkold(entry);
+                       /* NOTE: this may set soft-dirty too on some archs */
+                       if (dirty)
+                               entry = pte_mkdirty(entry);
                        if (soft_dirty)
                                entry = pte_mksoft_dirty(entry);
                        if (uffd_wp)