[PATCH 08/10] huge pagecache: extend mremap pmd rmap lockout to files

Hugh Dickins
2016-04-05T20:52:52Z

Whatever huge pagecache implementation we go with, file rmap locking
must be added to anon rmap locking, when mremap's move_page_tables()
finds a pmd_trans_huge pmd entry: a simple change, let's do it now.

Factor out take_rmap_locks() and drop_rmap_locks() to handle the
locking for make move_ptes() and move_page_tables(), and delete
the VM_BUG_ON_VMA which rejected vm_file and required anon_vma.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/mremap.c | 42 ++++++++++++++++++++++--------------------
1 file changed, 22 insertions(+), 20 deletions(-)

--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -70,6 +70,22 @@ static pmd_t *alloc_new_pmd(struct mm_st
return pmd;
}

+static void take_rmap_locks(struct vm_area_struct *vma)
+{
+ if (vma->vm_file)
+ i_mmap_lock_write(vma->vm_file->f_mapping);
+ if (vma->anon_vma)
+ anon_vma_lock_write(vma->anon_vma);
+}
+
+static void drop_rmap_locks(struct vm_area_struct *vma)
+{
+ if (vma->anon_vma)
+ anon_vma_unlock_write(vma->anon_vma);
+ if (vma->vm_file)
+ i_mmap_unlock_write(vma->vm_file->f_mapping);
+}
+
static pte_t move_soft_dirty_pte(pte_t pte)
{
/*
@@ -90,8 +106,6 @@ static void move_ptes(struct vm_area_str
struct vm_area_struct *new_vma, pmd_t *new_pmd,
unsigned long new_addr, bool need_rmap_locks)
{
- struct address_space *mapping = NULL;
- struct anon_vma *anon_vma = NULL;
struct mm_struct *mm = vma->vm_mm;
pte_t *old_pte, *new_pte, pte;
spinlock_t *old_ptl, *new_ptl;
@@ -114,16 +128,8 @@ static void move_ptes(struct vm_area_str
* serialize access to individual ptes, but only rmap traversal
* order guarantees that we won't miss both the old and new ptes).
*/
- if (need_rmap_locks) {
- if (vma->vm_file) {
- mapping = vma->vm_file->f_mapping;
- i_mmap_lock_write(mapping);
- }
- if (vma->anon_vma) {
- anon_vma = vma->anon_vma;
- anon_vma_lock_write(anon_vma);
- }
- }
+ if (need_rmap_locks)
+ take_rmap_locks(vma);

/*
* We don't have to worry about the ordering of src and dst
@@ -151,10 +157,8 @@ static void move_ptes(struct vm_area_str
spin_unlock(new_ptl);
pte_unmap(new_pte - 1);
pte_unmap_unlock(old_pte - 1, old_ptl);
- if (anon_vma)
- anon_vma_unlock_write(anon_vma);
- if (mapping)
- i_mmap_unlock_write(mapping);
+ if (need_rmap_locks)
+ drop_rmap_locks(vma);
}

#define LATENCY_LIMIT (64 * PAGE_SIZE)
@@ -193,15 +197,13 @@ unsigned long move_page_tables(struct vm
if (pmd_trans_huge(*old_pmd)) {
if (extent == HPAGE_PMD_SIZE) {
bool moved;
- VM_BUG_ON_VMA(vma->vm_file || !vma->anon_vma,
- vma);
/* See comment in move_ptes() */
if (need_rmap_locks)
- anon_vma_lock_write(vma->anon_vma);
+ take_rmap_locks(vma);
moved = move_huge_pmd(vma, old_addr, new_addr,
old_end, old_pmd, new_pmd);
if (need_rmap_locks)
- anon_vma_unlock_write(vma->anon_vma);
+ drop_rmap_locks(vma);
if (moved) {
need_flush = true;
continue;