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authorDennis Zhou <dennis@kernel.org>2019-12-13 16:22:15 -0800
committerDavid Sterba <dsterba@suse.com>2020-01-20 16:40:57 +0100
commit6e80d4f8c422d3b2b0c37324d3243f5ed9b558c8 (patch)
tree3e10ee536d9846d17efcaf04fc6e0c5a6fc99c93 /fs/btrfs/ctree.h
parentbtrfs: add the beginning of async discard, discard workqueue (diff)
downloadlinux-dev-6e80d4f8c422d3b2b0c37324d3243f5ed9b558c8.tar.xz
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btrfs: handle empty block_group removal for async discard
block_group removal is a little tricky. It can race with the extent allocator, the cleaner thread, and balancing. The current path is for a block_group to be added to the unused_bgs list. Then, when the cleaner thread comes around, it starts a transaction and then proceeds with removing the block_group. Extents that are pinned are subsequently removed from the pinned trees and then eventually a discard is issued for the entire block_group. Async discard introduces another player into the game, the discard workqueue. While it has none of the racing issues, the new problem is ensuring we don't leave free space untrimmed prior to forgetting the block_group. This is handled by placing fully free block_groups on a separate discard queue. This is necessary to maintain discarding order as in the future we will slowly trim even fully free block_groups. The ordering helps us make progress on the same block_group rather than say the last fully freed block_group or needing to search through the fully freed block groups at the beginning of a list and insert after. The new order of events is a fully freed block group gets placed on the unused discard queue first. Once it's processed, it will be placed on the unusued_bgs list and then the original sequence of events will happen, just without the final whole block_group discard. The mount flags can change when processing unused_bgs, so when flipping from DISCARD to DISCARD_ASYNC, the unused_bgs must be punted to the discard_list to be trimmed. If we flip off DISCARD_ASYNC, we punt free block groups on the discard_list to the unused_bg queue which will do the final discard for us. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Dennis Zhou <dennis@kernel.org> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/ctree.h')
-rw-r--r--fs/btrfs/ctree.h9
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index f7b429277089..d15a4aa721aa 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -443,9 +443,14 @@ struct btrfs_full_stripe_locks_tree {
/* Discard control. */
/*
* Async discard uses multiple lists to differentiate the discard filter
- * parameters.
+ * parameters. Index 0 is for completely free block groups where we need to
+ * ensure the entire block group is trimmed without being lossy. Indices
+ * afterwards represent monotonically decreasing discard filter sizes to
+ * prioritize what should be discarded next.
*/
-#define BTRFS_NR_DISCARD_LISTS 1
+#define BTRFS_NR_DISCARD_LISTS 2
+#define BTRFS_DISCARD_INDEX_UNUSED 0
+#define BTRFS_DISCARD_INDEX_START 1
struct btrfs_discard_ctl {
struct workqueue_struct *discard_workers;