Btrfs: set page->private to the eb

We spend a lot of time looking up extent buffers from pages when we could just
store the pointer to the eb the page is associated with in page->private.  This
patch does just that, and it makes things a little simpler and reduces a bit of
CPU overhead involved with doing metadata IO.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

3 files changed, 91 insertions, 93 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 68fc93e18db8..bc88649cffb7 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -403,39 +403,28 @@ static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
         struct extent_io_tree *tree;
         u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
         u64 found_start;
-        unsigned long len;
         struct extent_buffer *eb;
 
         tree = &BTRFS_I(page->mapping->host)->io_tree;
 
-        if (page->private == EXTENT_PAGE_PRIVATE)
-                goto out;
-        if (!page->private) {
-                WARN_ON(1);
-                goto out;
-        }
-        len = page->private >> 2;
-        WARN_ON(len == 0);
-
-        eb = find_extent_buffer(tree, start, len);
+        eb = (struct extent_buffer *)page->private;
+        if (page != eb->pages[0])
+                return 0;
 
         found_start = btrfs_header_bytenr(eb);
         if (found_start != start) {
                 WARN_ON(1);
-                goto err;
+                return 0;
         }
         if (eb->pages[0] != page) {
                 WARN_ON(1);
-                goto err;
+                return 0;
         }
         if (!PageUptodate(page)) {
                 WARN_ON(1);
-                goto err;
+                return 0;
         }
         csum_tree_block(root, eb, 0);
-err:
-        free_extent_buffer(eb);
-out:
         return 0;
 }
 
@@ -566,7 +555,6 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
         struct extent_io_tree *tree;
         u64 found_start;
         int found_level;
-        unsigned long len;
         struct extent_buffer *eb;
         struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
         int ret = 0;
@@ -576,13 +564,8 @@ static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
                 goto out;
 
         tree = &BTRFS_I(page->mapping->host)->io_tree;
-        len = page->private >> 2;
+        eb = (struct extent_buffer *)page->private;
 
-        eb = find_eb_for_page(tree, page, max(root->leafsize, root->nodesize));
-        if (!eb) {
-                ret = -EIO;
-                goto out;
-        }
         reads_done = atomic_dec_and_test(&eb->pages_reading);
         if (!reads_done)
                 goto err;
@@ -631,7 +614,6 @@ err:
 
         if (ret && eb)
                 clear_extent_buffer_uptodate(tree, eb, NULL);
-        free_extent_buffer(eb);
 out:
         return ret;
 }
@@ -640,31 +622,17 @@ static int btree_io_failed_hook(struct bio *failed_bio,
                          struct page *page, u64 start, u64 end,
                          int mirror_num, struct extent_state *state)
 {
-        struct extent_io_tree *tree;
-        unsigned long len;
         struct extent_buffer *eb;
         struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
 
-        tree = &BTRFS_I(page->mapping->host)->io_tree;
-        if (page->private == EXTENT_PAGE_PRIVATE)
-                goto out;
-        if (!page->private)
-                goto out;
-
-        len = page->private >> 2;
-        WARN_ON(len == 0);
-
-        eb = alloc_extent_buffer(tree, start, len);
-        if (eb == NULL)
-                goto out;
+        eb = (struct extent_buffer *)page->private;
+        if (page != eb->pages[0])
+                return -EIO;
 
         if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
                 clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
                 btree_readahead_hook(root, eb, eb->start, -EIO);
         }
-        free_extent_buffer(eb);
-
-out:
         return -EIO;    /* we fixed nothing */
 }
 
@@ -955,10 +923,8 @@ static int btree_readpage(struct file *file, struct page *page)
 
 static int btree_releasepage(struct page *page, gfp_t gfp_flags)
 {
-        struct extent_io_tree *tree;
         struct extent_map_tree *map;
-        struct extent_buffer *eb;
-        struct btrfs_root *root;
+        struct extent_io_tree *tree;
         int ret;
 
         if (PageWriteback(page) || PageDirty(page))
@@ -967,13 +933,6 @@ 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;
 
-        root = BTRFS_I(page->mapping->host)->root;
-        if (page->private == EXTENT_PAGE_PRIVATE) {
-                eb = find_eb_for_page(tree, page, max(root->leafsize, root->nodesize));
-                free_extent_buffer(eb);
-                if (eb)
-                        return 0;
-        }
         /*
          * We need to mask out eg. __GFP_HIGHMEM and __GFP_DMA32 as we're doing
          * slab allocation from alloc_extent_state down the callchain where
@@ -985,14 +944,7 @@ static int btree_releasepage(struct page *page, gfp_t gfp_flags)
         if (!ret)
                 return 0;
 
-        ret = try_release_extent_buffer(tree, page);
-        if (ret == 1) {
-                ClearPagePrivate(page);
-                set_page_private(page, 0);
-                page_cache_release(page);
-        }
-
-        return ret;
+        return try_release_extent_buffer(tree, page);
 }
 
 static void btree_invalidatepage(struct page *page, unsigned long offset)
@@ -3219,17 +3171,21 @@ static int btree_lock_page_hook(struct page *page, void *data,
 {
         struct inode *inode = page->mapping->host;
         struct btrfs_root *root = BTRFS_I(inode)->root;
-        struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
         struct extent_buffer *eb;
-        unsigned long len;
-        u64 bytenr = page_offset(page);
 
-        if (page->private == EXTENT_PAGE_PRIVATE)
+        /*
+         * We culled this eb but the page is still hanging out on the mapping,
+         * carry on.
+         */
+        if (!PagePrivate(page))
                 goto out;
 
-        len = page->private >> 2;
-        eb = find_extent_buffer(io_tree, bytenr, len);
-        if (!eb)
+        eb = (struct extent_buffer *)page->private;
+        if (!eb) {
+                WARN_ON(1);
+                goto out;
+        }
+        if (page != eb->pages[0])
                 goto out;
 
         if (!btrfs_try_tree_write_lock(eb)) {
@@ -3248,7 +3204,6 @@ static int btree_lock_page_hook(struct page *page, void *data,
         }
 
         btrfs_tree_unlock(eb);
-        free_extent_buffer(eb);
 out:
         if (!trylock_page(page)) {
                 flush_fn(data);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c6c9ce463c86..0381b6007ae4 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2473,19 +2473,24 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
         return ret;
 }
 
-void set_page_extent_mapped(struct page *page)
+void attach_extent_buffer_page(struct extent_buffer *eb, struct page *page)
 {
         if (!PagePrivate(page)) {
                 SetPagePrivate(page);
                 page_cache_get(page);
-                set_page_private(page, EXTENT_PAGE_PRIVATE);
+                set_page_private(page, (unsigned long)eb);
+        } else {
+                WARN_ON(page->private != (unsigned long)eb);
         }
 }
 
-static void set_page_extent_head(struct page *page, unsigned long len)
+void set_page_extent_mapped(struct page *page)
 {
-        WARN_ON(!PagePrivate(page));
-        set_page_private(page, EXTENT_PAGE_PRIVATE_FIRST_PAGE | len << 2);
+        if (!PagePrivate(page)) {
+                SetPagePrivate(page);
+                page_cache_get(page);
+                set_page_private(page, EXTENT_PAGE_PRIVATE);
+        }
 }
 
 /*
@@ -3585,6 +3590,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
                 return NULL;
         eb->start = start;
         eb->len = len;
+        eb->tree = tree;
         rwlock_init(&eb->lock);
         atomic_set(&eb->write_locks, 0);
         atomic_set(&eb->read_locks, 0);
@@ -3637,8 +3643,31 @@ static void btrfs_release_extent_buffer_page(struct extent_buffer *eb,
         do {
                 index--;
                 page = extent_buffer_page(eb, index);
-                if (page)
+                if (page) {
+                        spin_lock(&page->mapping->private_lock);
+                        /*
+                         * We do this since we'll remove the pages after we've
+                         * removed the eb from the radix tree, so we could race
+                         * and have this page now attached to the new eb.  So
+                         * only clear page_private if it's still connected to
+                         * this eb.
+                         */
+                        if (PagePrivate(page) &&
+                            page->private == (unsigned long)eb) {
+                                /*
+                                 * We need to make sure we haven't be attached
+                                 * to a new eb.
+                                 */
+                                ClearPagePrivate(page);
+                                set_page_private(page, 0);
+                                /* One for the page private */
+                                page_cache_release(page);
+                        }
+                        spin_unlock(&page->mapping->private_lock);
+
+                        /* One for when we alloced the page */
                         page_cache_release(page);
+                }
         } while (index != start_idx);
 }
 
@@ -3683,6 +3712,32 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
                         WARN_ON(1);
                         goto free_eb;
                 }
+
+                spin_lock(&mapping->private_lock);
+                if (PagePrivate(p)) {
+                        /*
+                         * We could have already allocated an eb for this page
+                         * and attached one so lets see if we can get a ref on
+                         * the existing eb, and if we can we know it's good and
+                         * we can just return that one, else we know we can just
+                         * overwrite page->private.
+                         */
+                        exists = (struct extent_buffer *)p->private;
+                        if (atomic_inc_not_zero(&exists->refs)) {
+                                spin_unlock(&mapping->private_lock);
+                                unlock_page(p);
+                                goto free_eb;
+                        }
+
+                        /* 
+                         * Do this so attach doesn't complain and we need to
+                         * drop the ref the old guy had.
+                         */
+                        ClearPagePrivate(p);
+                        page_cache_release(p);
+                }
+                attach_extent_buffer_page(eb, p);
+                spin_unlock(&mapping->private_lock);
                 mark_page_accessed(p);
                 eb->pages[i] = p;
                 if (!PageUptodate(p))
@@ -3705,7 +3760,6 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
         if (ret == -EEXIST) {
                 exists = radix_tree_lookup(&tree->buffer,
                                                 start >> PAGE_CACHE_SHIFT);
-                /* add one reference for the caller */
                 atomic_inc(&exists->refs);
                 spin_unlock(&tree->buffer_lock);
                 radix_tree_preload_end();
@@ -3725,12 +3779,9 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
          * after the extent buffer is in the radix tree so
          * it doesn't get lost
          */
-        set_page_extent_mapped(eb->pages[0]);
-        set_page_extent_head(eb->pages[0], eb->len);
         SetPageChecked(eb->pages[0]);
         for (i = 1; i < num_pages; i++) {
                 p = extent_buffer_page(eb, i);
-                set_page_extent_mapped(p);
                 ClearPageChecked(p);
                 unlock_page(p);
         }
@@ -3794,10 +3845,6 @@ int clear_extent_buffer_dirty(struct extent_io_tree *tree,
                 lock_page(page);
                 WARN_ON(!PagePrivate(page));
 
-                set_page_extent_mapped(page);
-                if (i == 0)
-                        set_page_extent_head(page, eb->len);
-
                 clear_page_dirty_for_io(page);
                 spin_lock_irq(&page->mapping->tree_lock);
                 if (!PageDirty(page)) {
@@ -4010,9 +4057,6 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
         atomic_set(&eb->pages_reading, num_reads);
         for (i = start_i; i < num_pages; i++) {
                 page = extent_buffer_page(eb, i);
-                set_page_extent_mapped(page);
-                if (i == 0)
-                        set_page_extent_head(page, eb->len);
                 if (!PageUptodate(page)) {
                         ClearPageError(page);
                         err = __extent_read_full_page(tree, page,
@@ -4395,22 +4439,19 @@ static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
         struct extent_buffer *eb =
                         container_of(head, struct extent_buffer, rcu_head);
 
-        btrfs_release_extent_buffer(eb);
+        __free_extent_buffer(eb);
 }
 
 int try_release_extent_buffer(struct extent_io_tree *tree, struct page *page)
 {
         u64 start = page_offset(page);
-        struct extent_buffer *eb;
+        struct extent_buffer *eb = (struct extent_buffer *)page->private;
         int ret = 1;
 
-        spin_lock(&tree->buffer_lock);
-        eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
-        if (!eb) {
-                spin_unlock(&tree->buffer_lock);
-                return ret;
-        }
+        if (!PagePrivate(page) || !eb)
+                return 1;
 
+        spin_lock(&tree->buffer_lock);
         if (atomic_read(&eb->refs) > 1 ||
             test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
                 ret = 0;
@@ -4426,6 +4467,7 @@ int try_release_extent_buffer(struct extent_io_tree *tree, struct page *page)
                 goto out;
         }
         radix_tree_delete(&tree->buffer, start >> PAGE_CACHE_SHIFT);
+        btrfs_release_extent_buffer_page(eb, 0);
 out:
         spin_unlock(&tree->buffer_lock);
 
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 4e38a3d9631a..83e432da2e26 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -127,6 +127,7 @@ struct extent_buffer {
         unsigned long map_start;
         unsigned long map_len;
         unsigned long bflags;
+        struct extent_io_tree *tree;
         atomic_t refs;
         atomic_t pages_reading;
         struct list_head leak_list;