dax: Convert page fault handlers to XArray
authorMatthew Wilcox <willy@infradead.org>
Fri, 30 Mar 2018 02:58:27 +0000 (22:58 -0400)
committerMatthew Wilcox <willy@infradead.org>
Sun, 21 Oct 2018 14:46:44 +0000 (10:46 -0400)
This is the last part of DAX to be converted to the XArray so
remove all the old helper functions.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
fs/dax.c

index fc2745c..616e36e 100644 (file)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -93,12 +93,6 @@ static unsigned long dax_to_pfn(void *entry)
        return xa_to_value(entry) >> DAX_SHIFT;
 }
 
-static void *dax_make_locked(unsigned long pfn, unsigned long flags)
-{
-       return xa_mk_value(flags | ((unsigned long)pfn << DAX_SHIFT) |
-                       DAX_LOCKED);
-}
-
 static void *dax_make_entry(pfn_t pfn, unsigned long flags)
 {
        return xa_mk_value(flags | (pfn_t_to_pfn(pfn) << DAX_SHIFT));
@@ -155,10 +149,11 @@ struct wait_exceptional_entry_queue {
        struct exceptional_entry_key key;
 };
 
-static wait_queue_head_t *dax_entry_waitqueue(struct xarray *xa,
-               pgoff_t index, void *entry, struct exceptional_entry_key *key)
+static wait_queue_head_t *dax_entry_waitqueue(struct xa_state *xas,
+               void *entry, struct exceptional_entry_key *key)
 {
        unsigned long hash;
+       unsigned long index = xas->xa_index;
 
        /*
         * If 'entry' is a PMD, align the 'index' that we use for the wait
@@ -167,11 +162,10 @@ static wait_queue_head_t *dax_entry_waitqueue(struct xarray *xa,
         */
        if (dax_is_pmd_entry(entry))
                index &= ~PG_PMD_COLOUR;
-
-       key->xa = xa;
+       key->xa = xas->xa;
        key->entry_start = index;
 
-       hash = hash_long((unsigned long)xa ^ index, DAX_WAIT_TABLE_BITS);
+       hash = hash_long((unsigned long)xas->xa ^ index, DAX_WAIT_TABLE_BITS);
        return wait_table + hash;
 }
 
@@ -193,13 +187,12 @@ static int wake_exceptional_entry_func(wait_queue_entry_t *wait,
  * The important information it's conveying is whether the entry at
  * this index used to be a PMD entry.
  */
-static void dax_wake_mapping_entry_waiter(struct xarray *xa,
-               pgoff_t index, void *entry, bool wake_all)
+static void dax_wake_entry(struct xa_state *xas, void *entry, bool wake_all)
 {
        struct exceptional_entry_key key;
        wait_queue_head_t *wq;
 
-       wq = dax_entry_waitqueue(xa, index, entry, &key);
+       wq = dax_entry_waitqueue(xas, entry, &key);
 
        /*
         * Checking for locked entry and prepare_to_wait_exclusive() happens
@@ -211,12 +204,6 @@ static void dax_wake_mapping_entry_waiter(struct xarray *xa,
                __wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
 }
 
-static void dax_wake_entry(struct xa_state *xas, void *entry, bool wake_all)
-{
-       return dax_wake_mapping_entry_waiter(xas->xa, xas->xa_index, entry,
-                                                               wake_all);
-}
-
 /*
  * Look up entry in page cache, wait for it to become unlocked if it
  * is a DAX entry and return it.  The caller must subsequently call
@@ -241,8 +228,7 @@ static void *get_unlocked_entry(struct xa_state *xas)
                                !dax_is_locked(entry))
                        return entry;
 
-               wq = dax_entry_waitqueue(xas->xa, xas->xa_index, entry,
-                               &ewait.key);
+               wq = dax_entry_waitqueue(xas, entry, &ewait.key);
                prepare_to_wait_exclusive(wq, &ewait.wait,
                                          TASK_UNINTERRUPTIBLE);
                xas_unlock_irq(xas);
@@ -286,138 +272,6 @@ static void *dax_lock_entry(struct xa_state *xas, void *entry)
        return xas_store(xas, xa_mk_value(v | DAX_LOCKED));
 }
 
-/*
- * Check whether the given slot is locked.  Must be called with the i_pages
- * lock held.
- */
-static inline int slot_locked(struct address_space *mapping, void **slot)
-{
-       unsigned long entry = xa_to_value(
-               radix_tree_deref_slot_protected(slot, &mapping->i_pages.xa_lock));
-       return entry & DAX_LOCKED;
-}
-
-/*
- * Mark the given slot as locked.  Must be called with the i_pages lock held.
- */
-static inline void *lock_slot(struct address_space *mapping, void **slot)
-{
-       unsigned long v = xa_to_value(
-               radix_tree_deref_slot_protected(slot, &mapping->i_pages.xa_lock));
-       void *entry = xa_mk_value(v | DAX_LOCKED);
-       radix_tree_replace_slot(&mapping->i_pages, slot, entry);
-       return entry;
-}
-
-/*
- * Mark the given slot as unlocked.  Must be called with the i_pages lock held.
- */
-static inline void *unlock_slot(struct address_space *mapping, void **slot)
-{
-       unsigned long v = xa_to_value(
-               radix_tree_deref_slot_protected(slot, &mapping->i_pages.xa_lock));
-       void *entry = xa_mk_value(v & ~DAX_LOCKED);
-       radix_tree_replace_slot(&mapping->i_pages, slot, entry);
-       return entry;
-}
-
-/*
- * Lookup entry in page cache, wait for it to become unlocked if it is
- * a DAX entry and return it. The caller must call
- * put_unlocked_mapping_entry() when he decided not to lock the entry or
- * put_locked_mapping_entry() when he locked the entry and now wants to
- * unlock it.
- *
- * Must be called with the i_pages lock held.
- */
-static void *__get_unlocked_mapping_entry(struct address_space *mapping,
-               pgoff_t index, void ***slotp, bool (*wait_fn)(void))
-{
-       void *entry, **slot;
-       struct wait_exceptional_entry_queue ewait;
-       wait_queue_head_t *wq;
-
-       init_wait(&ewait.wait);
-       ewait.wait.func = wake_exceptional_entry_func;
-
-       for (;;) {
-               bool revalidate;
-
-               entry = __radix_tree_lookup(&mapping->i_pages, index, NULL,
-                                         &slot);
-               if (!entry ||
-                   WARN_ON_ONCE(!xa_is_value(entry)) ||
-                   !slot_locked(mapping, slot)) {
-                       if (slotp)
-                               *slotp = slot;
-                       return entry;
-               }
-
-               wq = dax_entry_waitqueue(&mapping->i_pages, index, entry,
-                               &ewait.key);
-               prepare_to_wait_exclusive(wq, &ewait.wait,
-                                         TASK_UNINTERRUPTIBLE);
-               xa_unlock_irq(&mapping->i_pages);
-               revalidate = wait_fn();
-               finish_wait(wq, &ewait.wait);
-               xa_lock_irq(&mapping->i_pages);
-               if (revalidate)
-                       return ERR_PTR(-EAGAIN);
-       }
-}
-
-static bool entry_wait(void)
-{
-       schedule();
-       /*
-        * Never return an ERR_PTR() from
-        * __get_unlocked_mapping_entry(), just keep looping.
-        */
-       return false;
-}
-
-static void *get_unlocked_mapping_entry(struct address_space *mapping,
-               pgoff_t index, void ***slotp)
-{
-       return __get_unlocked_mapping_entry(mapping, index, slotp, entry_wait);
-}
-
-static void unlock_mapping_entry(struct address_space *mapping, pgoff_t index)
-{
-       void *entry, **slot;
-
-       xa_lock_irq(&mapping->i_pages);
-       entry = __radix_tree_lookup(&mapping->i_pages, index, NULL, &slot);
-       if (WARN_ON_ONCE(!entry || !xa_is_value(entry) ||
-                        !slot_locked(mapping, slot))) {
-               xa_unlock_irq(&mapping->i_pages);
-               return;
-       }
-       unlock_slot(mapping, slot);
-       xa_unlock_irq(&mapping->i_pages);
-       dax_wake_mapping_entry_waiter(&mapping->i_pages, index, entry, false);
-}
-
-static void put_locked_mapping_entry(struct address_space *mapping,
-               pgoff_t index)
-{
-       unlock_mapping_entry(mapping, index);
-}
-
-/*
- * Called when we are done with page cache entry we looked up via
- * get_unlocked_mapping_entry() and which we didn't lock in the end.
- */
-static void put_unlocked_mapping_entry(struct address_space *mapping,
-                                      pgoff_t index, void *entry)
-{
-       if (!entry)
-               return;
-
-       /* We have to wake up next waiter for the page cache entry lock */
-       dax_wake_mapping_entry_waiter(&mapping->i_pages, index, entry, false);
-}
-
 static unsigned long dax_entry_size(void *entry)
 {
        if (dax_is_zero_entry(entry))
@@ -558,47 +412,52 @@ void dax_unlock_mapping_entry(struct page *page)
  * that index, add a locked empty entry.
  *
  * When requesting an entry with size DAX_PMD, grab_mapping_entry() will
- * either return that locked entry or will return an error.  This error will
- * happen if there are any 4k entries within the 2MiB range that we are
- * requesting.
+ * either return that locked entry or will return VM_FAULT_FALLBACK.
+ * This will happen if there are any PTE entries within the PMD range
+ * that we are requesting.
  *
- * We always favor 4k entries over 2MiB entries. There isn't a flow where we
- * evict 4k entries in order to 'upgrade' them to a 2MiB entry.  A 2MiB
- * insertion will fail if it finds any 4k entries already in the tree, and a
- * 4k insertion will cause an existing 2MiB entry to be unmapped and
- * downgraded to 4k entries.  This happens for both 2MiB huge zero pages as
- * well as 2MiB empty entries.
+ * We always favor PTE entries over PMD entries. There isn't a flow where we
+ * evict PTE entries in order to 'upgrade' them to a PMD entry.  A PMD
+ * insertion will fail if it finds any PTE entries already in the tree, and a
+ * PTE insertion will cause an existing PMD entry to be unmapped and
+ * downgraded to PTE entries.  This happens for both PMD zero pages as
+ * well as PMD empty entries.
  *
- * The exception to this downgrade path is for 2MiB DAX PMD entries that have
- * real storage backing them.  We will leave these real 2MiB DAX entries in
- * the tree, and PTE writes will simply dirty the entire 2MiB DAX entry.
+ * The exception to this downgrade path is for PMD entries that have
+ * real storage backing them.  We will leave these real PMD entries in
+ * the tree, and PTE writes will simply dirty the entire PMD entry.
  *
  * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
  * persistent memory the benefit is doubtful. We can add that later if we can
  * show it helps.
+ *
+ * On error, this function does not return an ERR_PTR.  Instead it returns
+ * a VM_FAULT code, encoded as an xarray internal entry.  The ERR_PTR values
+ * overlap with xarray value entries.
  */
-static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
-               unsigned long size_flag)
+static void *grab_mapping_entry(struct xa_state *xas,
+               struct address_space *mapping, unsigned long size_flag)
 {
-       bool pmd_downgrade = false; /* splitting 2MiB entry into 4k entries? */
-       void *entry, **slot;
-
-restart:
-       xa_lock_irq(&mapping->i_pages);
-       entry = get_unlocked_mapping_entry(mapping, index, &slot);
+       unsigned long index = xas->xa_index;
+       bool pmd_downgrade = false; /* splitting PMD entry into PTE entries? */
+       void *entry;
 
-       if (WARN_ON_ONCE(entry && !xa_is_value(entry))) {
-               entry = ERR_PTR(-EIO);
-               goto out_unlock;
-       }
+retry:
+       xas_lock_irq(xas);
+       entry = get_unlocked_entry(xas);
+       if (xa_is_internal(entry))
+               goto fallback;
 
        if (entry) {
+               if (WARN_ON_ONCE(!xa_is_value(entry))) {
+                       xas_set_err(xas, EIO);
+                       goto out_unlock;
+               }
+
                if (size_flag & DAX_PMD) {
                        if (dax_is_pte_entry(entry)) {
-                               put_unlocked_mapping_entry(mapping, index,
-                                               entry);
-                               entry = ERR_PTR(-EEXIST);
-                               goto out_unlock;
+                               put_unlocked_entry(xas, entry);
+                               goto fallback;
                        }
                } else { /* trying to grab a PTE entry */
                        if (dax_is_pmd_entry(entry) &&
@@ -609,87 +468,57 @@ restart:
                }
        }
 
-       /* No entry for given index? Make sure radix tree is big enough. */
-       if (!entry || pmd_downgrade) {
-               int err;
-
-               if (pmd_downgrade) {
-                       /*
-                        * Make sure 'entry' remains valid while we drop
-                        * the i_pages lock.
-                        */
-                       entry = lock_slot(mapping, slot);
-               }
+       if (pmd_downgrade) {
+               /*
+                * Make sure 'entry' remains valid while we drop
+                * the i_pages lock.
+                */
+               dax_lock_entry(xas, entry);
 
-               xa_unlock_irq(&mapping->i_pages);
                /*
                 * Besides huge zero pages the only other thing that gets
                 * downgraded are empty entries which don't need to be
                 * unmapped.
                 */
-               if (pmd_downgrade && dax_is_zero_entry(entry))
-                       unmap_mapping_pages(mapping, index & ~PG_PMD_COLOUR,
-                                                       PG_PMD_NR, false);
-
-               err = radix_tree_preload(
-                               mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
-               if (err) {
-                       if (pmd_downgrade)
-                               put_locked_mapping_entry(mapping, index);
-                       return ERR_PTR(err);
-               }
-               xa_lock_irq(&mapping->i_pages);
-
-               if (!entry) {
-                       /*
-                        * We needed to drop the i_pages lock while calling
-                        * radix_tree_preload() and we didn't have an entry to
-                        * lock.  See if another thread inserted an entry at
-                        * our index during this time.
-                        */
-                       entry = __radix_tree_lookup(&mapping->i_pages, index,
-                                       NULL, &slot);
-                       if (entry) {
-                               radix_tree_preload_end();
-                               xa_unlock_irq(&mapping->i_pages);
-                               goto restart;
-                       }
+               if (dax_is_zero_entry(entry)) {
+                       xas_unlock_irq(xas);
+                       unmap_mapping_pages(mapping,
+                                       xas->xa_index & ~PG_PMD_COLOUR,
+                                       PG_PMD_NR, false);
+                       xas_reset(xas);
+                       xas_lock_irq(xas);
                }
 
-               if (pmd_downgrade) {
-                       dax_disassociate_entry(entry, mapping, false);
-                       radix_tree_delete(&mapping->i_pages, index);
-                       mapping->nrexceptional--;
-                       dax_wake_mapping_entry_waiter(&mapping->i_pages,
-                                       index, entry, true);
-               }
+               dax_disassociate_entry(entry, mapping, false);
+               xas_store(xas, NULL);   /* undo the PMD join */
+               dax_wake_entry(xas, entry, true);
+               mapping->nrexceptional--;
+               entry = NULL;
+               xas_set(xas, index);
+       }
 
-               entry = dax_make_locked(0, size_flag | DAX_EMPTY);
-
-               err = __radix_tree_insert(&mapping->i_pages, index,
-                               dax_entry_order(entry), entry);
-               radix_tree_preload_end();
-               if (err) {
-                       xa_unlock_irq(&mapping->i_pages);
-                       /*
-                        * Our insertion of a DAX entry failed, most likely
-                        * because we were inserting a PMD entry and it
-                        * collided with a PTE sized entry at a different
-                        * index in the PMD range.  We haven't inserted
-                        * anything into the radix tree and have no waiters to
-                        * wake.
-                        */
-                       return ERR_PTR(err);
-               }
-               /* Good, we have inserted empty locked entry into the tree. */
+       if (entry) {
+               dax_lock_entry(xas, entry);
+       } else {
+               entry = dax_make_entry(pfn_to_pfn_t(0), size_flag | DAX_EMPTY);
+               dax_lock_entry(xas, entry);
+               if (xas_error(xas))
+                       goto out_unlock;
                mapping->nrexceptional++;
-               xa_unlock_irq(&mapping->i_pages);
-               return entry;
        }
-       entry = lock_slot(mapping, slot);
- out_unlock:
-       xa_unlock_irq(&mapping->i_pages);
+
+out_unlock:
+       xas_unlock_irq(xas);
+       if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM))
+               goto retry;
+       if (xas->xa_node == XA_ERROR(-ENOMEM))
+               return xa_mk_internal(VM_FAULT_OOM);
+       if (xas_error(xas))
+               return xa_mk_internal(VM_FAULT_SIGBUS);
        return entry;
+fallback:
+       xas_unlock_irq(xas);
+       return xa_mk_internal(VM_FAULT_FALLBACK);
 }
 
 /**
@@ -847,29 +676,27 @@ static int copy_user_dax(struct block_device *bdev, struct dax_device *dax_dev,
  * already in the tree, we will skip the insertion and just dirty the PMD as
  * appropriate.
  */
-static void *dax_insert_entry(struct address_space *mapping,
-               struct vm_fault *vmf,
-               void *entry, pfn_t pfn_t, unsigned long flags, bool dirty)
+static void *dax_insert_entry(struct xa_state *xas,
+               struct address_space *mapping, struct vm_fault *vmf,
+               void *entry, pfn_t pfn, unsigned long flags, bool dirty)
 {
-       struct radix_tree_root *pages = &mapping->i_pages;
-       unsigned long pfn = pfn_t_to_pfn(pfn_t);
-       pgoff_t index = vmf->pgoff;
-       void *new_entry;
+       void *new_entry = dax_make_entry(pfn, flags);
 
        if (dirty)
                __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 
        if (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE)) {
+               unsigned long index = xas->xa_index;
                /* we are replacing a zero page with block mapping */
                if (dax_is_pmd_entry(entry))
                        unmap_mapping_pages(mapping, index & ~PG_PMD_COLOUR,
-                                                       PG_PMD_NR, false);
+                                       PG_PMD_NR, false);
                else /* pte entry */
-                       unmap_mapping_pages(mapping, vmf->pgoff, 1, false);
+                       unmap_mapping_pages(mapping, index, 1, false);
        }
 
-       xa_lock_irq(pages);
-       new_entry = dax_make_locked(pfn, flags);
+       xas_reset(xas);
+       xas_lock_irq(xas);
        if (dax_entry_size(entry) != dax_entry_size(new_entry)) {
                dax_disassociate_entry(entry, mapping, false);
                dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
@@ -884,21 +711,18 @@ static void *dax_insert_entry(struct address_space *mapping,
                 * existing entry is a PMD, we will just leave the PMD in the
                 * tree and dirty it if necessary.
                 */
-               struct radix_tree_node *node;
-               void **slot;
-               void *ret;
-
-               ret = __radix_tree_lookup(pages, index, &node, &slot);
-               WARN_ON_ONCE(ret != entry);
-               __radix_tree_replace(pages, node, slot,
-                                    new_entry, NULL);
+               void *old = dax_lock_entry(xas, new_entry);
+               WARN_ON_ONCE(old != xa_mk_value(xa_to_value(entry) |
+                                       DAX_LOCKED));
                entry = new_entry;
+       } else {
+               xas_load(xas);  /* Walk the xa_state */
        }
 
        if (dirty)
-               radix_tree_tag_set(pages, index, PAGECACHE_TAG_DIRTY);
+               xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
 
-       xa_unlock_irq(pages);
+       xas_unlock_irq(xas);
        return entry;
 }
 
@@ -1166,15 +990,16 @@ out:
  * If this page is ever written to we will re-fault and change the mapping to
  * point to real DAX storage instead.
  */
-static vm_fault_t dax_load_hole(struct address_space *mapping, void *entry,
-                        struct vm_fault *vmf)
+static vm_fault_t dax_load_hole(struct xa_state *xas,
+               struct address_space *mapping, void **entry,
+               struct vm_fault *vmf)
 {
        struct inode *inode = mapping->host;
        unsigned long vaddr = vmf->address;
        pfn_t pfn = pfn_to_pfn_t(my_zero_pfn(vaddr));
        vm_fault_t ret;
 
-       dax_insert_entry(mapping, vmf, entry, pfn,
+       *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
                        DAX_ZERO_PAGE, false);
 
        ret = vmf_insert_mixed(vmf->vma, vaddr, pfn);
@@ -1384,6 +1209,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 {
        struct vm_area_struct *vma = vmf->vma;
        struct address_space *mapping = vma->vm_file->f_mapping;
+       XA_STATE(xas, &mapping->i_pages, vmf->pgoff);
        struct inode *inode = mapping->host;
        unsigned long vaddr = vmf->address;
        loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
@@ -1410,9 +1236,9 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
        if (write && !vmf->cow_page)
                flags |= IOMAP_WRITE;
 
-       entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
-       if (IS_ERR(entry)) {
-               ret = dax_fault_return(PTR_ERR(entry));
+       entry = grab_mapping_entry(&xas, mapping, 0);
+       if (xa_is_internal(entry)) {
+               ret = xa_to_internal(entry);
                goto out;
        }
 
@@ -1485,7 +1311,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
                if (error < 0)
                        goto error_finish_iomap;
 
-               entry = dax_insert_entry(mapping, vmf, entry, pfn,
+               entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
                                                 0, write && !sync);
 
                /*
@@ -1513,7 +1339,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
        case IOMAP_UNWRITTEN:
        case IOMAP_HOLE:
                if (!write) {
-                       ret = dax_load_hole(mapping, entry, vmf);
+                       ret = dax_load_hole(&xas, mapping, &entry, vmf);
                        goto finish_iomap;
                }
                /*FALLTHRU*/
@@ -1540,21 +1366,20 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
                ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap);
        }
  unlock_entry:
-       put_locked_mapping_entry(mapping, vmf->pgoff);
+       dax_unlock_entry(&xas, entry);
  out:
        trace_dax_pte_fault_done(inode, vmf, ret);
        return ret | major;
 }
 
 #ifdef CONFIG_FS_DAX_PMD
-static vm_fault_t dax_pmd_load_hole(struct vm_fault *vmf, struct iomap *iomap,
-               void *entry)
+static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
+               struct iomap *iomap, void **entry)
 {
        struct address_space *mapping = vmf->vma->vm_file->f_mapping;
        unsigned long pmd_addr = vmf->address & PMD_MASK;
        struct inode *inode = mapping->host;
        struct page *zero_page;
-       void *ret = NULL;
        spinlock_t *ptl;
        pmd_t pmd_entry;
        pfn_t pfn;
@@ -1565,7 +1390,7 @@ static vm_fault_t dax_pmd_load_hole(struct vm_fault *vmf, struct iomap *iomap,
                goto fallback;
 
        pfn = page_to_pfn_t(zero_page);
-       ret = dax_insert_entry(mapping, vmf, entry, pfn,
+       *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
                        DAX_PMD | DAX_ZERO_PAGE, false);
 
        ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
@@ -1578,11 +1403,11 @@ static vm_fault_t dax_pmd_load_hole(struct vm_fault *vmf, struct iomap *iomap,
        pmd_entry = pmd_mkhuge(pmd_entry);
        set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
        spin_unlock(ptl);
-       trace_dax_pmd_load_hole(inode, vmf, zero_page, ret);
+       trace_dax_pmd_load_hole(inode, vmf, zero_page, *entry);
        return VM_FAULT_NOPAGE;
 
 fallback:
-       trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, ret);
+       trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
        return VM_FAULT_FALLBACK;
 }
 
@@ -1591,6 +1416,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 {
        struct vm_area_struct *vma = vmf->vma;
        struct address_space *mapping = vma->vm_file->f_mapping;
+       XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_ORDER);
        unsigned long pmd_addr = vmf->address & PMD_MASK;
        bool write = vmf->flags & FAULT_FLAG_WRITE;
        bool sync;
@@ -1598,7 +1424,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
        struct inode *inode = mapping->host;
        vm_fault_t result = VM_FAULT_FALLBACK;
        struct iomap iomap = { 0 };
-       pgoff_t max_pgoff, pgoff;
+       pgoff_t max_pgoff;
        void *entry;
        loff_t pos;
        int error;
@@ -1609,7 +1435,6 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
         * supposed to hold locks serializing us with truncate / punch hole so
         * this is a reliable test.
         */
-       pgoff = linear_page_index(vma, pmd_addr);
        max_pgoff = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 
        trace_dax_pmd_fault(inode, vmf, max_pgoff, 0);
@@ -1634,24 +1459,26 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
        if ((pmd_addr + PMD_SIZE) > vma->vm_end)
                goto fallback;
 
-       if (pgoff >= max_pgoff) {
+       if (xas.xa_index >= max_pgoff) {
                result = VM_FAULT_SIGBUS;
                goto out;
        }
 
        /* If the PMD would extend beyond the file size */
-       if ((pgoff | PG_PMD_COLOUR) >= max_pgoff)
+       if ((xas.xa_index | PG_PMD_COLOUR) >= max_pgoff)
                goto fallback;
 
        /*
-        * grab_mapping_entry() will make sure we get a 2MiB empty entry, a
-        * 2MiB zero page entry or a DAX PMD.  If it can't (because a 4k page
-        * is already in the tree, for instance), it will return -EEXIST and
-        * we just fall back to 4k entries.
+        * grab_mapping_entry() will make sure we get an empty PMD entry,
+        * a zero PMD entry or a DAX PMD.  If it can't (because a PTE
+        * entry is already in the array, for instance), it will return
+        * VM_FAULT_FALLBACK.
         */
-       entry = grab_mapping_entry(mapping, pgoff, DAX_PMD);
-       if (IS_ERR(entry))
+       entry = grab_mapping_entry(&xas, mapping, DAX_PMD);
+       if (xa_is_internal(entry)) {
+               result = xa_to_internal(entry);
                goto fallback;
+       }
 
        /*
         * It is possible, particularly with mixed reads & writes to private
@@ -1670,7 +1497,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
         * setting up a mapping, so really we're using iomap_begin() as a way
         * to look up our filesystem block.
         */
-       pos = (loff_t)pgoff << PAGE_SHIFT;
+       pos = (loff_t)xas.xa_index << PAGE_SHIFT;
        error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap);
        if (error)
                goto unlock_entry;
@@ -1686,7 +1513,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
                if (error < 0)
                        goto finish_iomap;
 
-               entry = dax_insert_entry(mapping, vmf, entry, pfn,
+               entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
                                                DAX_PMD, write && !sync);
 
                /*
@@ -1711,7 +1538,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
        case IOMAP_HOLE:
                if (WARN_ON_ONCE(write))
                        break;
-               result = dax_pmd_load_hole(vmf, &iomap, entry);
+               result = dax_pmd_load_hole(&xas, vmf, &iomap, &entry);
                break;
        default:
                WARN_ON_ONCE(1);
@@ -1734,7 +1561,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
                                &iomap);
        }
  unlock_entry:
-       put_locked_mapping_entry(mapping, pgoff);
+       dax_unlock_entry(&xas, entry);
  fallback:
        if (result == VM_FAULT_FALLBACK) {
                split_huge_pmd(vma, vmf->pmd, vmf->address);