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btrfs: do not allow reservations if we have pending tickets

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If we already have tickets on the list we don't want to steal their
reservations.  This is a preparation patch for upcoming changes,
technically this shouldn't happen today because of the way we add bytes
to tickets before adding them to the space_info in most cases.

This does not change the FIFO nature of reserve tickets, it simply
allows us to enforce it in a different way.  Previously it was enforced
because any new space would be added to the first ticket on the list,
which would result in new reservations getting a reserve ticket.  This
replaces that mechanism by simply checking to see if we have outstanding
reserve tickets and skipping straight to adding a ticket for our
reservation.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2019-08-22 15:10:54 -04:00 committed by David Sterba
parent e182163d9c
commit ef1317a1b9
1 changed files with 7 additions and 3 deletions
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10
fs/btrfs/space-info.c
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@ -993,6 +993,7 @@ static int __reserve_metadata_bytes(struct btrfs_fs_info *fs_info,
struct reserve_ticket ticket;
u64 used;
int ret = 0;
bool pending_tickets;
ASSERT(orig_bytes);
ASSERT(!current->journal_info || flush != BTRFS_RESERVE_FLUSH_ALL);
@ -1000,14 +1001,17 @@ static int __reserve_metadata_bytes(struct btrfs_fs_info *fs_info,
spin_lock(&space_info->lock);
ret = -ENOSPC;
used = btrfs_space_info_used(space_info, true);
pending_tickets = !list_empty(&space_info->tickets) ||
!list_empty(&space_info->priority_tickets);
/*
* Carry on if we have enough space (short-circuit) OR call
* can_overcommit() to ensure we can overcommit to continue.
*/
if ((used + orig_bytes <= space_info->total_bytes) ||
can_overcommit(fs_info, space_info, orig_bytes, flush,
system_chunk)) {
if (!pending_tickets &&
((used + orig_bytes <= space_info->total_bytes) ||
can_overcommit(fs_info, space_info, orig_bytes, flush,
system_chunk))) {
btrfs_space_info_update_bytes_may_use(fs_info, space_info,
orig_bytes);
trace_btrfs_space_reservation(fs_info, "space_info",