Btrfs: Cache free inode numbers in memory
Currently btrfs stores the highest objectid of the fs tree, and it always
returns (highest+1) inode number when we create a file, so inode numbers
won't be reclaimed when we delete files, so we'll run out of inode numbers
as we keep create/delete files in 32bits machines.
This fixes it, and it works similarly to how we cache free space in block
cgroups.
We start a kernel thread to read the file tree. By scanning inode items,
we know which chunks of inode numbers are free, and we cache them in
an rb-tree.
Because we are searching the commit root, we have to carefully handle the
cross-transaction case.
The rb-tree is a hybrid extent+bitmap tree, so if we have too many small
chunks of inode numbers, we'll use bitmaps. Initially we allow 16K ram
of extents, and a bitmap will be used if we exceed this threshold. The
extents threshold is adjusted in runtime.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
index c05a08f..5be62df 100644
--- a/fs/btrfs/inode-map.c
+++ b/fs/btrfs/inode-map.c
@@ -16,11 +16,343 @@
* Boston, MA 021110-1307, USA.
*/
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/pagemap.h>
+
#include "ctree.h"
#include "disk-io.h"
+#include "free-space-cache.h"
+#include "inode-map.h"
#include "transaction.h"
-int btrfs_find_highest_inode(struct btrfs_root *root, u64 *objectid)
+static int caching_kthread(void *data)
+{
+ struct btrfs_root *root = data;
+ struct btrfs_fs_info *fs_info = root->fs_info;
+ struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
+ struct btrfs_key key;
+ struct btrfs_path *path;
+ struct extent_buffer *leaf;
+ u64 last = (u64)-1;
+ int slot;
+ int ret;
+
+ path = btrfs_alloc_path();
+ if (!path)
+ return -ENOMEM;
+
+ /* Since the commit root is read-only, we can safely skip locking. */
+ path->skip_locking = 1;
+ path->search_commit_root = 1;
+ path->reada = 2;
+
+ key.objectid = BTRFS_FIRST_FREE_OBJECTID;
+ key.offset = 0;
+ key.type = BTRFS_INODE_ITEM_KEY;
+again:
+ /* need to make sure the commit_root doesn't disappear */
+ mutex_lock(&root->fs_commit_mutex);
+
+ ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+ if (ret < 0)
+ goto out;
+
+ while (1) {
+ smp_mb();
+ if (fs_info->closing > 1)
+ goto out;
+
+ leaf = path->nodes[0];
+ slot = path->slots[0];
+ if (path->slots[0] >= btrfs_header_nritems(leaf)) {
+ ret = btrfs_next_leaf(root, path);
+ if (ret < 0)
+ goto out;
+ else if (ret > 0)
+ break;
+
+ if (need_resched() ||
+ btrfs_transaction_in_commit(fs_info)) {
+ leaf = path->nodes[0];
+
+ if (btrfs_header_nritems(leaf) == 0) {
+ WARN_ON(1);
+ break;
+ }
+
+ /*
+ * Save the key so we can advances forward
+ * in the next search.
+ */
+ btrfs_item_key_to_cpu(leaf, &key, 0);
+ btrfs_release_path(root, path);
+ root->cache_progress = last;
+ mutex_unlock(&root->fs_commit_mutex);
+ schedule_timeout(1);
+ goto again;
+ } else
+ continue;
+ }
+
+ btrfs_item_key_to_cpu(leaf, &key, slot);
+
+ if (key.type != BTRFS_INODE_ITEM_KEY)
+ goto next;
+
+ if (key.objectid >= BTRFS_LAST_FREE_OBJECTID)
+ break;
+
+ if (last != (u64)-1 && last + 1 != key.objectid) {
+ __btrfs_add_free_space(ctl, last + 1,
+ key.objectid - last - 1);
+ wake_up(&root->cache_wait);
+ }
+
+ last = key.objectid;
+next:
+ path->slots[0]++;
+ }
+
+ if (last < BTRFS_LAST_FREE_OBJECTID - 1) {
+ __btrfs_add_free_space(ctl, last + 1,
+ BTRFS_LAST_FREE_OBJECTID - last - 1);
+ }
+
+ spin_lock(&root->cache_lock);
+ root->cached = BTRFS_CACHE_FINISHED;
+ spin_unlock(&root->cache_lock);
+
+ root->cache_progress = (u64)-1;
+ btrfs_unpin_free_ino(root);
+out:
+ wake_up(&root->cache_wait);
+ mutex_unlock(&root->fs_commit_mutex);
+
+ btrfs_free_path(path);
+
+ return ret;
+}
+
+static void start_caching(struct btrfs_root *root)
+{
+ struct task_struct *tsk;
+
+ spin_lock(&root->cache_lock);
+ if (root->cached != BTRFS_CACHE_NO) {
+ spin_unlock(&root->cache_lock);
+ return;
+ }
+
+ root->cached = BTRFS_CACHE_STARTED;
+ spin_unlock(&root->cache_lock);
+
+ tsk = kthread_run(caching_kthread, root, "btrfs-ino-cache-%llu\n",
+ root->root_key.objectid);
+ BUG_ON(IS_ERR(tsk));
+}
+
+int btrfs_find_free_ino(struct btrfs_root *root, u64 *objectid)
+{
+again:
+ *objectid = btrfs_find_ino_for_alloc(root);
+
+ if (*objectid != 0)
+ return 0;
+
+ start_caching(root);
+
+ wait_event(root->cache_wait,
+ root->cached == BTRFS_CACHE_FINISHED ||
+ root->free_ino_ctl->free_space > 0);
+
+ if (root->cached == BTRFS_CACHE_FINISHED &&
+ root->free_ino_ctl->free_space == 0)
+ return -ENOSPC;
+ else
+ goto again;
+}
+
+void btrfs_return_ino(struct btrfs_root *root, u64 objectid)
+{
+ struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
+ struct btrfs_free_space_ctl *pinned = root->free_ino_pinned;
+again:
+ if (root->cached == BTRFS_CACHE_FINISHED) {
+ __btrfs_add_free_space(ctl, objectid, 1);
+ } else {
+ /*
+ * If we are in the process of caching free ino chunks,
+ * to avoid adding the same inode number to the free_ino
+ * tree twice due to cross transaction, we'll leave it
+ * in the pinned tree until a transaction is committed
+ * or the caching work is done.
+ */
+
+ mutex_lock(&root->fs_commit_mutex);
+ spin_lock(&root->cache_lock);
+ if (root->cached == BTRFS_CACHE_FINISHED) {
+ spin_unlock(&root->cache_lock);
+ mutex_unlock(&root->fs_commit_mutex);
+ goto again;
+ }
+ spin_unlock(&root->cache_lock);
+
+ start_caching(root);
+
+ if (objectid <= root->cache_progress)
+ __btrfs_add_free_space(ctl, objectid, 1);
+ else
+ __btrfs_add_free_space(pinned, objectid, 1);
+
+ mutex_unlock(&root->fs_commit_mutex);
+ }
+}
+
+/*
+ * When a transaction is committed, we'll move those inode numbers which
+ * are smaller than root->cache_progress from pinned tree to free_ino tree,
+ * and others will just be dropped, because the commit root we were
+ * searching has changed.
+ *
+ * Must be called with root->fs_commit_mutex held
+ */
+void btrfs_unpin_free_ino(struct btrfs_root *root)
+{
+ struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
+ struct rb_root *rbroot = &root->free_ino_pinned->free_space_offset;
+ struct btrfs_free_space *info;
+ struct rb_node *n;
+ u64 count;
+
+ while (1) {
+ n = rb_first(rbroot);
+ if (!n)
+ break;
+
+ info = rb_entry(n, struct btrfs_free_space, offset_index);
+ BUG_ON(info->bitmap);
+
+ if (info->offset > root->cache_progress)
+ goto free;
+ else if (info->offset + info->bytes > root->cache_progress)
+ count = root->cache_progress - info->offset + 1;
+ else
+ count = info->bytes;
+
+ __btrfs_add_free_space(ctl, info->offset, count);
+free:
+ rb_erase(&info->offset_index, rbroot);
+ kfree(info);
+ }
+}
+
+#define INIT_THRESHOLD (((1024 * 32) / 2) / sizeof(struct btrfs_free_space))
+#define INODES_PER_BITMAP (PAGE_CACHE_SIZE * 8)
+
+/*
+ * The goal is to keep the memory used by the free_ino tree won't
+ * exceed the memory if we use bitmaps only.
+ */
+static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
+{
+ struct btrfs_free_space *info;
+ struct rb_node *n;
+ int max_ino;
+ int max_bitmaps;
+
+ n = rb_last(&ctl->free_space_offset);
+ if (!n) {
+ ctl->extents_thresh = INIT_THRESHOLD;
+ return;
+ }
+ info = rb_entry(n, struct btrfs_free_space, offset_index);
+
+ /*
+ * Find the maximum inode number in the filesystem. Note we
+ * ignore the fact that this can be a bitmap, because we are
+ * not doing precise calculation.
+ */
+ max_ino = info->bytes - 1;
+
+ max_bitmaps = ALIGN(max_ino, INODES_PER_BITMAP) / INODES_PER_BITMAP;
+ if (max_bitmaps <= ctl->total_bitmaps) {
+ ctl->extents_thresh = 0;
+ return;
+ }
+
+ ctl->extents_thresh = (max_bitmaps - ctl->total_bitmaps) *
+ PAGE_CACHE_SIZE / sizeof(*info);
+}
+
+/*
+ * We don't fall back to bitmap, if we are below the extents threshold
+ * or this chunk of inode numbers is a big one.
+ */
+static bool use_bitmap(struct btrfs_free_space_ctl *ctl,
+ struct btrfs_free_space *info)
+{
+ if (ctl->free_extents < ctl->extents_thresh ||
+ info->bytes > INODES_PER_BITMAP / 10)
+ return false;
+
+ return true;
+}
+
+static struct btrfs_free_space_op free_ino_op = {
+ .recalc_thresholds = recalculate_thresholds,
+ .use_bitmap = use_bitmap,
+};
+
+static void pinned_recalc_thresholds(struct btrfs_free_space_ctl *ctl)
+{
+}
+
+static bool pinned_use_bitmap(struct btrfs_free_space_ctl *ctl,
+ struct btrfs_free_space *info)
+{
+ /*
+ * We always use extents for two reasons:
+ *
+ * - The pinned tree is only used during the process of caching
+ * work.
+ * - Make code simpler. See btrfs_unpin_free_ino().
+ */
+ return false;
+}
+
+static struct btrfs_free_space_op pinned_free_ino_op = {
+ .recalc_thresholds = pinned_recalc_thresholds,
+ .use_bitmap = pinned_use_bitmap,
+};
+
+void btrfs_init_free_ino_ctl(struct btrfs_root *root)
+{
+ struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
+ struct btrfs_free_space_ctl *pinned = root->free_ino_pinned;
+
+ spin_lock_init(&ctl->tree_lock);
+ ctl->unit = 1;
+ ctl->start = 0;
+ ctl->private = NULL;
+ ctl->op = &free_ino_op;
+
+ /*
+ * Initially we allow to use 16K of ram to cache chunks of
+ * inode numbers before we resort to bitmaps. This is somewhat
+ * arbitrary, but it will be adjusted in runtime.
+ */
+ ctl->extents_thresh = INIT_THRESHOLD;
+
+ spin_lock_init(&pinned->tree_lock);
+ pinned->unit = 1;
+ pinned->start = 0;
+ pinned->private = NULL;
+ pinned->extents_thresh = 0;
+ pinned->op = &pinned_free_ino_op;
+}
+
+static int btrfs_find_highest_objectid(struct btrfs_root *root, u64 *objectid)
{
struct btrfs_path *path;
int ret;
@@ -55,15 +387,14 @@
return ret;
}
-int btrfs_find_free_objectid(struct btrfs_trans_handle *trans,
- struct btrfs_root *root,
- u64 dirid, u64 *objectid)
+int btrfs_find_free_objectid(struct btrfs_root *root, u64 *objectid)
{
int ret;
mutex_lock(&root->objectid_mutex);
if (unlikely(root->highest_objectid < BTRFS_FIRST_FREE_OBJECTID)) {
- ret = btrfs_find_highest_inode(root, &root->highest_objectid);
+ ret = btrfs_find_highest_objectid(root,
+ &root->highest_objectid);
if (ret)
goto out;
}