Btrfs: rework how we reserve metadata bytes

With multi-threaded writes we were getting ENOSPC early because somebody would
come in, start flushing delalloc because they couldn't make their reservation,
and in the meantime other threads would come in and use the space that was
getting freed up, so when the original thread went to check to see if they had
space they didn't and they'd return ENOSPC.  So instead if we have some free
space but not enough for our reservation, take the reservation and then start
doing the flushing.  The only time we don't take reservations is when we've
already overcommitted our space, that way we don't have people who come late to
the party way overcommitting ourselves.  This also moves all of the retrying and
flushing code into reserve_metdata_bytes so it's all uniform.  This keeps my
fs_mark test from returning -ENOSPC as soon as it starts and actually lets me
fill up the disk.  Thanks,

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

1 files changed, 129 insertions, 109 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index aca3314ef8b9..180a50146ddf 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3078,38 +3078,6 @@ out:
         return ret;
 }
 
-static int maybe_allocate_chunk(struct btrfs_trans_handle *trans,
-                                struct btrfs_root *root,
-                                struct btrfs_space_info *sinfo, u64 num_bytes)
-{
-        int ret;
-        int end_trans = 0;
-
-        if (sinfo->full)
-                return 0;
-
-        spin_lock(&sinfo->lock);
-        ret = should_alloc_chunk(sinfo, num_bytes + 2 * 1024 * 1024);
-        spin_unlock(&sinfo->lock);
-        if (!ret)
-                return 0;
-
-        if (!trans) {
-                trans = btrfs_join_transaction(root, 1);
-                BUG_ON(IS_ERR(trans));
-                end_trans = 1;
-        }
-
-        ret = do_chunk_alloc(trans, root->fs_info->extent_root,
-                             num_bytes + 2 * 1024 * 1024,
-                             get_alloc_profile(root, sinfo->flags), 0);
-
-        if (end_trans)
-                btrfs_end_transaction(trans, root);
-
-        return ret == 1 ? 1 : 0;
-}
-
 /*
  * shrink metadata reservation for delalloc
  */
@@ -3167,79 +3135,138 @@ static int shrink_delalloc(struct btrfs_trans_handle *trans,
         return reclaimed >= to_reclaim;
 }
 
-static int should_retry_reserve(struct btrfs_trans_handle *trans,
-                                struct btrfs_root *root,
-                                struct btrfs_block_rsv *block_rsv,
-                                u64 num_bytes, int *retries)
+/*
+ * Retries tells us how many times we've called reserve_metadata_bytes.  The
+ * idea is if this is the first call (retries == 0) then we will add to our
+ * reserved count if we can't make the allocation in order to hold our place
+ * while we go and try and free up space.  That way for retries > 1 we don't try
+ * and add space, we just check to see if the amount of unused space is >= the
+ * total space, meaning that our reservation is valid.
+ *
+ * However if we don't intend to retry this reservation, pass -1 as retries so
+ * that it short circuits this logic.
+ */
+static int reserve_metadata_bytes(struct btrfs_trans_handle *trans,
+                                  struct btrfs_root *root,
+                                  struct btrfs_block_rsv *block_rsv,
+                                  u64 orig_bytes, int flush)
 {
         struct btrfs_space_info *space_info = block_rsv->space_info;
-        int ret;
+        u64 unused;
+        u64 num_bytes = orig_bytes;
+        int retries = 0;
+        int ret = 0;
+        bool reserved = false;
 
-        if ((*retries) > 2)
-                return -ENOSPC;
+again:
+        ret = -ENOSPC;
+        if (reserved)
+                num_bytes = 0;
 
-        ret = maybe_allocate_chunk(trans, root, space_info, num_bytes);
-        if (ret)
-                return 1;
+        spin_lock(&space_info->lock);
+        unused = space_info->bytes_used + space_info->bytes_reserved +
+                 space_info->bytes_pinned + space_info->bytes_readonly +
+                 space_info->bytes_may_use;
 
-        if (trans && trans->transaction->in_commit)
-                return -ENOSPC;
+        /*
+         * The idea here is that we've not already over-reserved the block group
+         * then we can go ahead and save our reservation first and then start
+         * flushing if we need to.  Otherwise if we've already overcommitted
+         * lets start flushing stuff first and then come back and try to make
+         * our reservation.
+         */
+        if (unused <= space_info->total_bytes) {
+                unused -= space_info->total_bytes;
+                if (unused >= num_bytes) {
+                        if (!reserved)
+                                space_info->bytes_reserved += orig_bytes;
+                        ret = 0;
+                } else {
+                        /*
+                         * Ok set num_bytes to orig_bytes since we aren't
+                         * overocmmitted, this way we only try and reclaim what
+                         * we need.
+                         */
+                        num_bytes = orig_bytes;
+                }
+        } else {
+                /*
+                 * Ok we're over committed, set num_bytes to the overcommitted
+                 * amount plus the amount of bytes that we need for this
+                 * reservation.
+                 */
+                num_bytes = unused - space_info->total_bytes +
+                        (orig_bytes * (retries + 1));
+        }
 
-        ret = shrink_delalloc(trans, root, num_bytes, 0);
-        if (ret)
-                return ret;
+        /*
+         * Couldn't make our reservation, save our place so while we're trying
+         * to reclaim space we can actually use it instead of somebody else
+         * stealing it from us.
+         */
+        if (ret && !reserved) {
+                space_info->bytes_reserved += orig_bytes;
+                reserved = true;
+        }
 
-        spin_lock(&space_info->lock);
-        if (space_info->bytes_pinned < num_bytes)
-                ret = 1;
         spin_unlock(&space_info->lock);
-        if (ret)
-                return -ENOSPC;
-
-        (*retries)++;
 
-        if (trans)
-                return -EAGAIN;
+        if (!ret)
+                return 0;
 
-        trans = btrfs_join_transaction(root, 1);
-        BUG_ON(IS_ERR(trans));
-        ret = btrfs_commit_transaction(trans, root);
-        BUG_ON(ret);
+        if (!flush)
+                goto out;
 
-        return 1;
-}
+        /*
+         * We do synchronous shrinking since we don't actually unreserve
+         * metadata until after the IO is completed.
+         */
+        ret = shrink_delalloc(trans, root, num_bytes, 1);
+        if (ret > 0)
+                return 0;
+        else if (ret < 0)
+                goto out;
 
-static int reserve_metadata_bytes(struct btrfs_block_rsv *block_rsv,
-                                  u64 num_bytes)
-{
-        struct btrfs_space_info *space_info = block_rsv->space_info;
-        u64 unused;
-        int ret = -ENOSPC;
+        /*
+         * So if we were overcommitted it's possible that somebody else flushed
+         * out enough space and we simply didn't have enough space to reclaim,
+         * so go back around and try again.
+         */
+        if (retries < 2) {
+                retries++;
+                goto again;
+        }
 
         spin_lock(&space_info->lock);
-        unused = space_info->bytes_used + space_info->bytes_reserved +
-                 space_info->bytes_pinned + space_info->bytes_readonly +
-                 space_info->bytes_may_use;
+        /*
+         * Not enough space to be reclaimed, don't bother committing the
+         * transaction.
+         */
+        if (space_info->bytes_pinned < orig_bytes)
+                ret = -ENOSPC;
+        spin_unlock(&space_info->lock);
+        if (ret)
+                goto out;
 
-        if (unused < space_info->total_bytes)
-                unused = space_info->total_bytes - unused;
-        else
-                unused = 0;
+        ret = -EAGAIN;
+        if (trans)
+                goto out;
 
-        if (unused >= num_bytes) {
-                if (block_rsv->priority >= 10) {
-                        space_info->bytes_reserved += num_bytes;
-                        ret = 0;
-                } else {
-                        if ((unused + block_rsv->reserved) *
-                            block_rsv->priority >=
-                            (num_bytes + block_rsv->reserved) * 10) {
-                                space_info->bytes_reserved += num_bytes;
-                                ret = 0;
-                        }
-                }
+
+        ret = -ENOSPC;
+        trans = btrfs_join_transaction(root, 1);
+        if (IS_ERR(trans))
+                goto out;
+        ret = btrfs_commit_transaction(trans, root);
+        if (!ret)
+                goto again;
+
+out:
+        if (reserved) {
+                spin_lock(&space_info->lock);
+                space_info->bytes_reserved -= orig_bytes;
+                spin_unlock(&space_info->lock);
         }
-        spin_unlock(&space_info->lock);
 
         return ret;
 }
@@ -3383,23 +3410,19 @@ void btrfs_add_durable_block_rsv(struct btrfs_fs_info *fs_info,
 int btrfs_block_rsv_add(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root,
                         struct btrfs_block_rsv *block_rsv,
-                        u64 num_bytes, int *retries)
+                        u64 num_bytes)
 {
         int ret;
 
         if (num_bytes == 0)
                 return 0;
-again:
-        ret = reserve_metadata_bytes(block_rsv, num_bytes);
+
+        ret = reserve_metadata_bytes(trans, root, block_rsv, num_bytes, 1);
         if (!ret) {
                 block_rsv_add_bytes(block_rsv, num_bytes, 1);
                 return 0;
         }
 
-        ret = should_retry_reserve(trans, root, block_rsv, num_bytes, retries);
-        if (ret > 0)
-                goto again;
-
         return ret;
 }
 
@@ -3434,7 +3457,8 @@ int btrfs_block_rsv_check(struct btrfs_trans_handle *trans,
                 return 0;
 
         if (block_rsv->refill_used) {
-                ret = reserve_metadata_bytes(block_rsv, num_bytes);
+                ret = reserve_metadata_bytes(trans, root, block_rsv,
+                                             num_bytes, 0);
                 if (!ret) {
                         block_rsv_add_bytes(block_rsv, num_bytes, 0);
                         return 0;
@@ -3614,7 +3638,7 @@ static u64 calc_trans_metadata_size(struct btrfs_root *root, int num_items)
 
 int btrfs_trans_reserve_metadata(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
-                                 int num_items, int *retries)
+                                 int num_items)
 {
         u64 num_bytes;
         int ret;
@@ -3624,7 +3648,7 @@ int btrfs_trans_reserve_metadata(struct btrfs_trans_handle *trans,
 
         num_bytes = calc_trans_metadata_size(root, num_items);
         ret = btrfs_block_rsv_add(trans, root, &root->fs_info->trans_block_rsv,
-                                  num_bytes, retries);
+                                  num_bytes);
         if (!ret) {
                 trans->bytes_reserved += num_bytes;
                 trans->block_rsv = &root->fs_info->trans_block_rsv;
@@ -3698,14 +3722,13 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
         struct btrfs_block_rsv *block_rsv = &root->fs_info->delalloc_block_rsv;
         u64 to_reserve;
         int nr_extents;
-        int retries = 0;
         int ret;
 
         if (btrfs_transaction_in_commit(root->fs_info))
                 schedule_timeout(1);
 
         num_bytes = ALIGN(num_bytes, root->sectorsize);
-again:
+
         spin_lock(&BTRFS_I(inode)->accounting_lock);
         nr_extents = atomic_read(&BTRFS_I(inode)->outstanding_extents) + 1;
         if (nr_extents > BTRFS_I(inode)->reserved_extents) {
@@ -3715,18 +3738,14 @@ again:
                 nr_extents = 0;
                 to_reserve = 0;
         }
+        spin_unlock(&BTRFS_I(inode)->accounting_lock);
 
         to_reserve += calc_csum_metadata_size(inode, num_bytes);
-        ret = reserve_metadata_bytes(block_rsv, to_reserve);
-        if (ret) {
-                spin_unlock(&BTRFS_I(inode)->accounting_lock);
-                ret = should_retry_reserve(NULL, root, block_rsv, to_reserve,
-                                           &retries);
-                if (ret > 0)
-                        goto again;
+        ret = reserve_metadata_bytes(NULL, root, block_rsv, to_reserve, 1);
+        if (ret)
                 return ret;
-        }
 
+        spin_lock(&BTRFS_I(inode)->accounting_lock);
         BTRFS_I(inode)->reserved_extents += nr_extents;
         atomic_inc(&BTRFS_I(inode)->outstanding_extents);
         spin_unlock(&BTRFS_I(inode)->accounting_lock);
@@ -5325,7 +5344,8 @@ use_block_rsv(struct btrfs_trans_handle *trans,
         block_rsv = get_block_rsv(trans, root);
 
         if (block_rsv->size == 0) {
-                ret = reserve_metadata_bytes(block_rsv, blocksize);
+                ret = reserve_metadata_bytes(trans, root, block_rsv,
+                                             blocksize, 0);
                 if (ret)
                         return ERR_PTR(ret);
                 return block_rsv;