Btrfs: Don't drop extent_map cache during releasepage on the btree inode

The btree inode should only have a single extent_map in the cache,
it doesn't make sense to ever drop it.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

3 files changed, 44 insertions, 20 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 76ee7a4ae00c..2de2b00afebc 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -76,13 +76,12 @@ struct extent_map *btree_get_extent(struct inode *inode, struct page *page,
         struct extent_map *em;
         int ret;
 
-again:
         spin_lock(&em_tree->lock);
         em = lookup_extent_mapping(em_tree, start, len);
         spin_unlock(&em_tree->lock);
-        if (em) {
+        if (em)
                 goto out;
-        }
+
         em = alloc_extent_map(GFP_NOFS);
         if (!em) {
                 em = ERR_PTR(-ENOMEM);
@@ -95,15 +94,21 @@ again:
 
         spin_lock(&em_tree->lock);
         ret = add_extent_mapping(em_tree, em);
-        spin_unlock(&em_tree->lock);
-
         if (ret == -EEXIST) {
                 free_extent_map(em);
-                em = NULL;
-                goto again;
+                em = lookup_extent_mapping(em_tree, start, len);
+                if (em)
+                        ret = 0;
+                else
+                        ret = -EIO;
         } else if (ret) {
-                em = ERR_PTR(ret);
+                free_extent_map(em);
+                em = NULL;
         }
+        spin_unlock(&em_tree->lock);
+
+        if (ret)
+                em = ERR_PTR(ret);
 out:
         return em;
 }
@@ -496,7 +501,7 @@ static int btree_releasepage(struct page *page, gfp_t gfp_flags)
         }
         tree = &BTRFS_I(page->mapping->host)->io_tree;
         map = &BTRFS_I(page->mapping->host)->extent_tree;
-        ret = try_release_extent_mapping(map, tree, page, gfp_flags);
+        ret = try_release_extent_state(map, tree, page, gfp_flags);
         if (ret == 1) {
                 invalidate_extent_lru(tree, page_offset(page), PAGE_CACHE_SIZE);
                 ClearPagePrivate(page);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a984a7bc1197..81f8b4fd069b 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2464,6 +2464,31 @@ err:
 EXPORT_SYMBOL(extent_prepare_write);
 
 /*
+ * a helper for releasepage, this tests for areas of the page that
+ * are locked or under IO and drops the related state bits if it is safe
+ * to drop the page.
+ */
+int try_release_extent_state(struct extent_map_tree *map,
+                             struct extent_io_tree *tree, struct page *page,
+                             gfp_t mask)
+{
+        u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
+        u64 end = start + PAGE_CACHE_SIZE - 1;
+        int ret = 1;
+
+        if (test_range_bit(tree, start, end, EXTENT_IOBITS, 0))
+                ret = 0;
+        else {
+                if ((mask & GFP_NOFS) == GFP_NOFS)
+                        mask = GFP_NOFS;
+                clear_extent_bit(tree, start, end, EXTENT_UPTODATE,
+                                 1, 1, mask);
+        }
+        return ret;
+}
+EXPORT_SYMBOL(try_release_extent_state);
+
+/*
  * a helper for releasepage.  As long as there are no locked extents
  * in the range corresponding to the page, both state records and extent
  * map records are removed
@@ -2475,8 +2500,7 @@ int try_release_extent_mapping(struct extent_map_tree *map,
         struct extent_map *em;
         u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
         u64 end = start + PAGE_CACHE_SIZE - 1;
-        u64 orig_start = start;
-        int ret = 1;
+
         if ((mask & __GFP_WAIT) &&
             page->mapping->host->i_size > 16 * 1024 * 1024) {
                 u64 len;
@@ -2507,15 +2531,7 @@ int try_release_extent_mapping(struct extent_map_tree *map,
                         free_extent_map(em);
                 }
         }
-        if (test_range_bit(tree, orig_start, end, EXTENT_IOBITS, 0))
-                ret = 0;
-        else {
-                if ((mask & GFP_NOFS) == GFP_NOFS)
-                        mask = GFP_NOFS;
-                clear_extent_bit(tree, orig_start, end, EXTENT_UPTODATE,
-                                 1, 1, mask);
-        }
-        return ret;
+        return try_release_extent_state(map, tree, page, mask);
 }
 EXPORT_SYMBOL(try_release_extent_mapping);
 
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 232300d13be2..e48346147514 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -110,6 +110,9 @@ void extent_io_tree_empty_lru(struct extent_io_tree *tree);
 int try_release_extent_mapping(struct extent_map_tree *map,
                                struct extent_io_tree *tree, struct page *page,
                                gfp_t mask);
+int try_release_extent_state(struct extent_map_tree *map,
+                             struct extent_io_tree *tree, struct page *page,
+                             gfp_t mask);
 int lock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask);
 int unlock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask);
 int extent_read_full_page(struct extent_io_tree *tree, struct page *page,