From 114623979405abf0b143f9c6688b3ff00ee48338 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 11 Aug 2021 14:37:16 -0400 Subject: btrfs: do not do preemptive flushing if the majority is global rsv 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 Signed-off-by: David Sterba --- fs/btrfs/space-info.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'fs/btrfs') diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c index cab532a48bcd..5ada02e0e629 100644 --- a/fs/btrfs/space-info.c +++ b/fs/btrfs/space-info.c @@ -741,6 +741,20 @@ static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info, 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. -- cgit v1.2.3