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btrfs: introduce tickets_id to determine whether asynchronous metadata reclaim work makes progress

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In btrfs_async_reclaim_metadata_space(), we use ticket's address to
determine whether asynchronous metadata reclaim work is making progress.

	ticket = list_first_entry(&space_info->tickets,
				  struct reserve_ticket, list);
	if (last_ticket == ticket) {
		flush_state++;
	} else {
		last_ticket = ticket;
		flush_state = FLUSH_DELAYED_ITEMS_NR;
		if (commit_cycles)
			commit_cycles--;
	}

But indeed it's wrong, we should not rely on local variable's address to
do this check, because addresses may be same. In my test environment, I
dd one 168MB file in a 256MB fs, found that for this file, every time
wait_reserve_ticket() called, local variable ticket's address is same,

For above codes, assume a previous ticket's address is addrA, last_ticket
is addrA. Btrfs_async_reclaim_metadata_space() finished this ticket and
wake up it, then another ticket is added, but with the same address addrA,
now last_ticket will be same to current ticket, then current ticket's flush
work will start from current flush_state, not initial FLUSH_DELAYED_ITEMS_NR,
which may result in some enospc issues(I have seen this in my test machine).

Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Wang Xiaoguang 2016-09-02 10:58:46 +08:00 committed by David Sterba
parent ed7a694839
commit ce129655c9
2 changed files with 7 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/btrfs/ctree.h
View File

@ -427,6 +427,7 @@ struct btrfs_space_info {
struct list_head ro_bgs;
struct list_head priority_tickets;
struct list_head tickets;
u64 tickets_id;
struct rw_semaphore groups_sem;
/* for block groups in our same type */

11
fs/btrfs/extent-tree.c
View File

@ -4966,12 +4966,12 @@ static void wake_all_tickets(struct list_head *head)
*/
static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
{
struct reserve_ticket *last_ticket = NULL;
struct btrfs_fs_info *fs_info;
struct btrfs_space_info *space_info;
u64 to_reclaim;
int flush_state;
int commit_cycles = 0;
u64 last_tickets_id;
fs_info = container_of(work, struct btrfs_fs_info, async_reclaim_work);
space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
@ -4984,8 +4984,7 @@ static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
spin_unlock(&space_info->lock);
return;
}
last_ticket = list_first_entry(&space_info->tickets,
struct reserve_ticket, list);
last_tickets_id = space_info->tickets_id;
spin_unlock(&space_info->lock);
flush_state = FLUSH_DELAYED_ITEMS_NR;
@ -5005,10 +5004,10 @@ static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
space_info);
ticket = list_first_entry(&space_info->tickets,
struct reserve_ticket, list);
if (last_ticket == ticket) {
if (last_tickets_id == space_info->tickets_id) {
flush_state++;
} else {
last_ticket = ticket;
last_tickets_id = space_info->tickets_id;
flush_state = FLUSH_DELAYED_ITEMS_NR;
if (commit_cycles)
commit_cycles--;
@ -5384,6 +5383,7 @@ again:
list_del_init(&ticket->list);
num_bytes -= ticket->bytes;
ticket->bytes = 0;
space_info->tickets_id++;
wake_up(&ticket->wait);
} else {
ticket->bytes -= num_bytes;
@ -5426,6 +5426,7 @@ again:
num_bytes -= ticket->bytes;
space_info->bytes_may_use += ticket->bytes;
ticket->bytes = 0;
space_info->tickets_id++;
wake_up(&ticket->wait);
} else {
trace_btrfs_space_reservation(fs_info, "space_info",