Btrfs: create special free space cache inode

In order to save free space cache, we need an inode to hold the data, and we
need a special item to point at the right inode for the right block group.  So
first, create a special item that will point to the right inode, and the number
of extent entries we will have and the number of bitmaps we will have.  We
truncate and pre-allocate space everytime to make sure it's uptodate.

This feature will be turned on as soon as you mount with -o space_cache, however
it is safe to boot into old kernels, they will just generate the cache the old
fashion way.  When you boot back into a newer kernel we will notice that we
modified and not the cache and automatically discard the cache.

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

1 files changed, 225 insertions, 6 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 32d094002a57..aab40fb3faed 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2688,6 +2688,109 @@ next_block_group(struct btrfs_root *root,
         return cache;
 }
 
+static int cache_save_setup(struct btrfs_block_group_cache *block_group,
+                            struct btrfs_trans_handle *trans,
+                            struct btrfs_path *path)
+{
+        struct btrfs_root *root = block_group->fs_info->tree_root;
+        struct inode *inode = NULL;
+        u64 alloc_hint = 0;
+        int num_pages = 0;
+        int retries = 0;
+        int ret = 0;
+
+        /*
+         * If this block group is smaller than 100 megs don't bother caching the
+         * block group.
+         */
+        if (block_group->key.offset < (100 * 1024 * 1024)) {
+                spin_lock(&block_group->lock);
+                block_group->disk_cache_state = BTRFS_DC_WRITTEN;
+                spin_unlock(&block_group->lock);
+                return 0;
+        }
+
+again:
+        inode = lookup_free_space_inode(root, block_group, path);
+        if (IS_ERR(inode) && PTR_ERR(inode) != -ENOENT) {
+                ret = PTR_ERR(inode);
+                btrfs_release_path(root, path);
+                goto out;
+        }
+
+        if (IS_ERR(inode)) {
+                BUG_ON(retries);
+                retries++;
+
+                if (block_group->ro)
+                        goto out_free;
+
+                ret = create_free_space_inode(root, trans, block_group, path);
+                if (ret)
+                        goto out_free;
+                goto again;
+        }
+
+        /*
+         * We want to set the generation to 0, that way if anything goes wrong
+         * from here on out we know not to trust this cache when we load up next
+         * time.
+         */
+        BTRFS_I(inode)->generation = 0;
+        ret = btrfs_update_inode(trans, root, inode);
+        WARN_ON(ret);
+
+        if (i_size_read(inode) > 0) {
+                ret = btrfs_truncate_free_space_cache(root, trans, path,
+                                                      inode);
+                if (ret)
+                        goto out_put;
+        }
+
+        spin_lock(&block_group->lock);
+        if (block_group->cached != BTRFS_CACHE_FINISHED) {
+                spin_unlock(&block_group->lock);
+                goto out_put;
+        }
+        spin_unlock(&block_group->lock);
+
+        num_pages = (int)div64_u64(block_group->key.offset, 1024 * 1024 * 1024);
+        if (!num_pages)
+                num_pages = 1;
+
+        /*
+         * Just to make absolutely sure we have enough space, we're going to
+         * preallocate 12 pages worth of space for each block group.  In
+         * practice we ought to use at most 8, but we need extra space so we can
+         * add our header and have a terminator between the extents and the
+         * bitmaps.
+         */
+        num_pages *= 16;
+        num_pages *= PAGE_CACHE_SIZE;
+
+        ret = btrfs_check_data_free_space(inode, num_pages);
+        if (ret)
+                goto out_put;
+
+        ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, num_pages,
+                                              num_pages, num_pages,
+                                              &alloc_hint);
+        btrfs_free_reserved_data_space(inode, num_pages);
+out_put:
+        iput(inode);
+out_free:
+        btrfs_release_path(root, path);
+out:
+        spin_lock(&block_group->lock);
+        if (ret)
+                block_group->disk_cache_state = BTRFS_DC_ERROR;
+        else
+                block_group->disk_cache_state = BTRFS_DC_SETUP;
+        spin_unlock(&block_group->lock);
+
+        return ret;
+}
+
 int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root)
 {
@@ -2700,6 +2803,25 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
         if (!path)
                 return -ENOMEM;
 
+again:
+        while (1) {
+                cache = btrfs_lookup_first_block_group(root->fs_info, last);
+                while (cache) {
+                        if (cache->disk_cache_state == BTRFS_DC_CLEAR)
+                                break;
+                        cache = next_block_group(root, cache);
+                }
+                if (!cache) {
+                        if (last == 0)
+                                break;
+                        last = 0;
+                        continue;
+                }
+                err = cache_save_setup(cache, trans, path);
+                last = cache->key.objectid + cache->key.offset;
+                btrfs_put_block_group(cache);
+        }
+
         while (1) {
                 if (last == 0) {
                         err = btrfs_run_delayed_refs(trans, root,
@@ -2709,6 +2831,11 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
 
                 cache = btrfs_lookup_first_block_group(root->fs_info, last);
                 while (cache) {
+                        if (cache->disk_cache_state == BTRFS_DC_CLEAR) {
+                                btrfs_put_block_group(cache);
+                                goto again;
+                        }
+
                         if (cache->dirty)
                                 break;
                         cache = next_block_group(root, cache);
@@ -2883,11 +3010,16 @@ int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
         struct btrfs_space_info *data_sinfo;
         struct btrfs_root *root = BTRFS_I(inode)->root;
         u64 used;
-        int ret = 0, committed = 0;
+        int ret = 0, committed = 0, alloc_chunk = 1;
 
         /* make sure bytes are sectorsize aligned */
         bytes = (bytes + root->sectorsize - 1) & ~((u64)root->sectorsize - 1);
 
+        if (root == root->fs_info->tree_root) {
+                alloc_chunk = 0;
+                committed = 1;
+        }
+
         data_sinfo = BTRFS_I(inode)->space_info;
         if (!data_sinfo)
                 goto alloc;
@@ -2906,7 +3038,7 @@ again:
                  * if we don't have enough free bytes in this space then we need
                  * to alloc a new chunk.
                  */
-                if (!data_sinfo->full) {
+                if (!data_sinfo->full && alloc_chunk) {
                         u64 alloc_target;
 
                         data_sinfo->force_alloc = 1;
@@ -3777,12 +3909,12 @@ static int update_block_group(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               u64 bytenr, u64 num_bytes, int alloc)
 {
-        struct btrfs_block_group_cache *cache;
+        struct btrfs_block_group_cache *cache = NULL;
         struct btrfs_fs_info *info = root->fs_info;
-        int factor;
         u64 total = num_bytes;
         u64 old_val;
         u64 byte_in_group;
+        int factor;
 
         /* block accounting for super block */
         spin_lock(&info->delalloc_lock);
@@ -3804,11 +3936,17 @@ static int update_block_group(struct btrfs_trans_handle *trans,
                         factor = 2;
                 else
                         factor = 1;
+
                 byte_in_group = bytenr - cache->key.objectid;
                 WARN_ON(byte_in_group > cache->key.offset);
 
                 spin_lock(&cache->space_info->lock);
                 spin_lock(&cache->lock);
+
+                if (btrfs_super_cache_generation(&info->super_copy) != 0 &&
+                    cache->disk_cache_state < BTRFS_DC_CLEAR)
+                        cache->disk_cache_state = BTRFS_DC_CLEAR;
+
                 cache->dirty = 1;
                 old_val = btrfs_block_group_used(&cache->item);
                 num_bytes = min(total, cache->key.offset - byte_in_group);
@@ -7814,6 +7952,40 @@ out:
         return ret;
 }
 
+void btrfs_put_block_group_cache(struct btrfs_fs_info *info)
+{
+        struct btrfs_block_group_cache *block_group;
+        u64 last = 0;
+
+        while (1) {
+                struct inode *inode;
+
+                block_group = btrfs_lookup_first_block_group(info, last);
+                while (block_group) {
+                        spin_lock(&block_group->lock);
+                        if (block_group->iref)
+                                break;
+                        spin_unlock(&block_group->lock);
+                        block_group = next_block_group(info->tree_root,
+                                                       block_group);
+                }
+                if (!block_group) {
+                        if (last == 0)
+                                break;
+                        last = 0;
+                        continue;
+                }
+
+                inode = block_group->inode;
+                block_group->iref = 0;
+                block_group->inode = NULL;
+                spin_unlock(&block_group->lock);
+                iput(inode);
+                last = block_group->key.objectid + block_group->key.offset;
+                btrfs_put_block_group(block_group);
+        }
+}
+
 int btrfs_free_block_groups(struct btrfs_fs_info *info)
 {
         struct btrfs_block_group_cache *block_group;
@@ -7897,6 +8069,8 @@ int btrfs_read_block_groups(struct btrfs_root *root)
         struct btrfs_key key;
         struct btrfs_key found_key;
         struct extent_buffer *leaf;
+        int need_clear = 0;
+        u64 cache_gen;
 
         root = info->extent_root;
         key.objectid = 0;
@@ -7906,6 +8080,11 @@ int btrfs_read_block_groups(struct btrfs_root *root)
         if (!path)
                 return -ENOMEM;
 
+        cache_gen = btrfs_super_cache_generation(&root->fs_info->super_copy);
+        if (cache_gen != 0 &&
+            btrfs_super_generation(&root->fs_info->super_copy) != cache_gen)
+                need_clear = 1;
+
         while (1) {
                 ret = find_first_block_group(root, path, &key);
                 if (ret > 0)
@@ -7928,6 +8107,9 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                 INIT_LIST_HEAD(&cache->list);
                 INIT_LIST_HEAD(&cache->cluster_list);
 
+                if (need_clear)
+                        cache->disk_cache_state = BTRFS_DC_CLEAR;
+
                 /*
                  * we only want to have 32k of ram per block group for keeping
                  * track of free space, and if we pass 1/2 of that we want to
@@ -8032,6 +8214,7 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
         cache->key.offset = size;
         cache->key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
         cache->sectorsize = root->sectorsize;
+        cache->fs_info = root->fs_info;
 
         /*
          * we only want to have 32k of ram per block group for keeping track
@@ -8088,7 +8271,9 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
         struct btrfs_path *path;
         struct btrfs_block_group_cache *block_group;
         struct btrfs_free_cluster *cluster;
+        struct btrfs_root *tree_root = root->fs_info->tree_root;
         struct btrfs_key key;
+        struct inode *inode;
         int ret;
 
         root = root->fs_info->extent_root;
@@ -8097,8 +8282,6 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
         BUG_ON(!block_group);
         BUG_ON(!block_group->ro);
 
-        memcpy(&key, &block_group->key, sizeof(key));
-
         /* make sure this block group isn't part of an allocation cluster */
         cluster = &root->fs_info->data_alloc_cluster;
         spin_lock(&cluster->refill_lock);
@@ -8117,6 +8300,40 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
         path = btrfs_alloc_path();
         BUG_ON(!path);
 
+        inode = lookup_free_space_inode(root, block_group, path);
+        if (!IS_ERR(inode)) {
+                btrfs_orphan_add(trans, inode);
+                clear_nlink(inode);
+                /* One for the block groups ref */
+                spin_lock(&block_group->lock);
+                if (block_group->iref) {
+                        block_group->iref = 0;
+                        block_group->inode = NULL;
+                        spin_unlock(&block_group->lock);
+                        iput(inode);
+                } else {
+                        spin_unlock(&block_group->lock);
+                }
+                /* One for our lookup ref */
+                iput(inode);
+        }
+
+        key.objectid = BTRFS_FREE_SPACE_OBJECTID;
+        key.offset = block_group->key.objectid;
+        key.type = 0;
+
+        ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1);
+        if (ret < 0)
+                goto out;
+        if (ret > 0)
+                btrfs_release_path(tree_root, path);
+        if (ret == 0) {
+                ret = btrfs_del_item(trans, tree_root, path);
+                if (ret)
+                        goto out;
+                btrfs_release_path(tree_root, path);
+        }
+
         spin_lock(&root->fs_info->block_group_cache_lock);
         rb_erase(&block_group->cache_node,
                  &root->fs_info->block_group_cache_tree);
@@ -8140,6 +8357,8 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
         block_group->space_info->bytes_readonly -= block_group->key.offset;
         spin_unlock(&block_group->space_info->lock);
 
+        memcpy(&key, &block_group->key, sizeof(key));
+
         btrfs_clear_space_info_full(root->fs_info);
 
         btrfs_put_block_group(block_group);