From: Josef Bacik josef@toxicpanda.com
commit 114623979405abf0b143f9c6688b3ff00ee48338 upstream.
A common characteristic of the bug report where preemptive flushing was going full tilt was the fact that the vast majority of the free metadata space was used up by the global reserve. The hard 90% threshold would cover the majority of these cases, but to be even smarter we should take into account how much of the outstanding reservations are covered by the global block reserve. If the global block reserve accounts for the vast majority of outstanding reservations, skip preemptive flushing, as it will likely just cause churn and pain.
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212185 Signed-off-by: Josef Bacik josef@toxicpanda.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/space-info.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
--- a/fs/btrfs/space-info.c +++ b/fs/btrfs/space-info.c @@ -741,6 +741,20 @@ static bool need_preemptive_reclaim(stru global_rsv_size) >= thresh) return false;
+ used = space_info->bytes_may_use + space_info->bytes_pinned; + + /* The total flushable belongs to the global rsv, don't flush. */ + if (global_rsv_size >= used) + return false; + + /* + * 128MiB is 1/4 of the maximum global rsv size. If we have less than + * that devoted to other reservations then there's no sense in flushing, + * we don't have a lot of things that need flushing. + */ + if (used - global_rsv_size <= SZ_128M) + return false; + /* * We have tickets queued, bail so we don't compete with the async * flushers.