thp: rewrite freeze_page()/unfreeze_page() with generic rmap walkers
freeze_page() and unfreeze_page() helpers evolved in rather complex
beasts. It would be nice to cut complexity of this code.
This patch rewrites freeze_page() using standard try_to_unmap().
unfreeze_page() is rewritten with remove_migration_ptes().
The result is much simpler.
But the new variant is somewhat slower for PTE-mapped THPs. Current
helpers iterates over VMAs the compound page is mapped to, and then over
ptes within this VMA. New helpers iterates over small page, then over
VMA the small page mapped to, and only then find relevant pte.
We have short cut for PMD-mapped THP: we directly install migration
entries on PMD split.
I don't think the slowdown is critical, considering how much simpler
result is and that split_huge_page() is quite rare nowadays. It only
happens due memory pressure or migration.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/rmap.c b/mm/rmap.c
index 945933a..c399a0d 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1431,8 +1431,14 @@
if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
goto out;
- if (flags & TTU_SPLIT_HUGE_PMD)
- split_huge_pmd_address(vma, address);
+ if (flags & TTU_SPLIT_HUGE_PMD) {
+ split_huge_pmd_address(vma, address,
+ flags & TTU_MIGRATION, page);
+ /* check if we have anything to do after split */
+ if (page_mapcount(page) == 0)
+ goto out;
+ }
+
pte = page_check_address(page, mm, address, &ptl, 0);
if (!pte)
goto out;