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authorJosef Bacik <jbacik@fb.com>2018-12-03 10:20:33 -0500
committerDavid Sterba <dsterba@suse.com>2018-12-17 14:51:46 +0100
commitba2c4d4e3bda7d6de2bc616ae6715e0a0725b294 (patch)
treec60d9ad52bf961acd6fe3d5400ea411a8302085d /fs/btrfs/transaction.c
parent158ffa364bf723fa1ef128060646d23dc3942994 (diff)
btrfs: introduce delayed_refs_rsv
Traditionally we've had voodoo in btrfs to account for the space that delayed refs may take up by having a global_block_rsv. This works most of the time, except when it doesn't. We've had issues reported and seen in production where sometimes the global reserve is exhausted during transaction commit before we can run all of our delayed refs, resulting in an aborted transaction. Because of this voodoo we have equally dubious flushing semantics around throttling delayed refs which we often get wrong. So instead give them their own block_rsv. This way we can always know exactly how much outstanding space we need for delayed refs. This allows us to make sure we are constantly filling that reservation up with space, and allows us to put more precise pressure on the enospc system. Instead of doing math to see if its a good time to throttle, the normal enospc code will be invoked if we have a lot of delayed refs pending, and they will be run via the normal flushing mechanism. For now the delayed_refs_rsv will hold the reservations for the delayed refs, the block group updates, and deleting csums. We could have a separate rsv for the block group updates, but the csum deletion stuff is still handled via the delayed_refs so that will stay there. Historical background: The global reserve has grown to cover everything we don't reserve space explicitly for, and we've grown a lot of weird ad-hoc heuristics to know if we're running short on space and when it's time to force a commit. A failure rate of 20-40 file systems when we run hundreds of thousands of them isn't super high, but cleaning up this code will make things less ugly and more predictible. Thus the delayed refs rsv. We always know how many delayed refs we have outstanding, and although running them generates more we can use the global reserve for that spill over, which fits better into it's desired use than a full blown reservation. This first approach is to simply take how many times we're reserving space for and multiply that by 2 in order to save enough space for the delayed refs that could be generated. This is a niave approach and will probably evolve, but for now it works. Signed-off-by: Josef Bacik <jbacik@fb.com> Reviewed-by: David Sterba <dsterba@suse.com> # high-level review [ added background notes from the cover letter ] Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/transaction.c')
-rw-r--r--fs/btrfs/transaction.c37
1 files changed, 34 insertions, 3 deletions
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 67e84939b758..e18eb75e6fa3 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -454,7 +454,7 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
bool enforce_qgroups)
{
struct btrfs_fs_info *fs_info = root->fs_info;
-
+ struct btrfs_block_rsv *delayed_refs_rsv = &fs_info->delayed_refs_rsv;
struct btrfs_trans_handle *h;
struct btrfs_transaction *cur_trans;
u64 num_bytes = 0;
@@ -483,13 +483,28 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
* the appropriate flushing if need be.
*/
if (num_items && root != fs_info->chunk_root) {
+ struct btrfs_block_rsv *rsv = &fs_info->trans_block_rsv;
+ u64 delayed_refs_bytes = 0;
+
qgroup_reserved = num_items * fs_info->nodesize;
ret = btrfs_qgroup_reserve_meta_pertrans(root, qgroup_reserved,
enforce_qgroups);
if (ret)
return ERR_PTR(ret);
+ /*
+ * We want to reserve all the bytes we may need all at once, so
+ * we only do 1 enospc flushing cycle per transaction start. We
+ * accomplish this by simply assuming we'll do 2 x num_items
+ * worth of delayed refs updates in this trans handle, and
+ * refill that amount for whatever is missing in the reserve.
+ */
num_bytes = btrfs_calc_trans_metadata_size(fs_info, num_items);
+ if (delayed_refs_rsv->full == 0) {
+ delayed_refs_bytes = num_bytes;
+ num_bytes <<= 1;
+ }
+
/*
* Do the reservation for the relocation root creation
*/
@@ -498,8 +513,24 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
reloc_reserved = true;
}
- ret = btrfs_block_rsv_add(root, &fs_info->trans_block_rsv,
- num_bytes, flush);
+ ret = btrfs_block_rsv_add(root, rsv, num_bytes, flush);
+ if (ret)
+ goto reserve_fail;
+ if (delayed_refs_bytes) {
+ btrfs_migrate_to_delayed_refs_rsv(fs_info, rsv,
+ delayed_refs_bytes);
+ num_bytes -= delayed_refs_bytes;
+ }
+ } else if (num_items == 0 && flush == BTRFS_RESERVE_FLUSH_ALL &&
+ !delayed_refs_rsv->full) {
+ /*
+ * Some people call with btrfs_start_transaction(root, 0)
+ * because they can be throttled, but have some other mechanism
+ * for reserving space. We still want these guys to refill the
+ * delayed block_rsv so just add 1 items worth of reservation
+ * here.
+ */
+ ret = btrfs_delayed_refs_rsv_refill(fs_info, flush);
if (ret)
goto reserve_fail;
}