@@ -777,11 +777,11 @@ btrfs_calc_reclaim_metadata_size(struct btrfs_fs_info *fs_info,
}
static inline bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
- struct btrfs_space_info *space_info,
- u64 used)
+ struct btrfs_space_info *space_info)
{
+ u64 ordered, delalloc;
u64 thresh = div_factor_fine(space_info->total_bytes, 98);
- u64 to_reclaim, expected;
+ u64 used;
/* If we're just plain full then async reclaim just slows us down. */
if ((space_info->bytes_used + space_info->bytes_reserved) >= thresh)
@@ -794,26 +794,52 @@ static inline bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
if (space_info->reclaim_size)
return 0;
- to_reclaim = min_t(u64, num_online_cpus() * SZ_1M, SZ_16M);
- if (btrfs_can_overcommit(fs_info, space_info, to_reclaim,
- BTRFS_RESERVE_FLUSH_ALL))
- return 0;
+ /*
+ * If we have over half of the free space occupied by reservations or
+ * pinned then we want to start flushing.
+ *
+ * We do not do the traditional thing here, which is to say
+ *
+ * if (used >= ((total_bytes + avail) >> 1))
+ * return 1;
+ *
+ * because this doesn't quite work how we want. If we had more than 50%
+ * of the space_info used by bytes_used and we had 0 available we'd just
+ * constantly run the background flusher. Instead we want it to kick in
+ * if our reclaimable space exceeds 50% of our available free space.
+ */
+ thresh = calc_available_free_space(fs_info, space_info,
+ BTRFS_RESERVE_FLUSH_ALL);
+ thresh += (space_info->total_bytes - space_info->bytes_used -
+ space_info->bytes_reserved - space_info->bytes_readonly);
+ thresh >>= 1;
- used = btrfs_space_info_used(space_info, true);
- if (btrfs_can_overcommit(fs_info, space_info, SZ_1M,
- BTRFS_RESERVE_FLUSH_ALL))
- expected = div_factor_fine(space_info->total_bytes, 95);
- else
- expected = div_factor_fine(space_info->total_bytes, 90);
+ used = space_info->bytes_pinned;
- if (used > expected)
- to_reclaim = used - expected;
+ /*
+ * If we have more ordered bytes than delalloc bytes then we're either
+ * doing a lot of DIO, or we simply don't have a lot of delalloc waiting
+ * around. Preemptive flushing is only useful in that it can free up
+ * space before tickets need to wait for things to finish. In the case
+ * of ordered extents, preemptively waiting on ordered extents gets us
+ * nothing, if our reservations are tied up in ordered extents we'll
+ * simply have to slow down writers by forcing them to wait on ordered
+ * extents.
+ *
+ * In the case that ordered is larger than delalloc, only include the
+ * block reserves that we would actually be able to directly reclaim
+ * from. In this case if we're heavy on metadata operations this will
+ * clearly be heavy enough to warrant preemptive flushing. In the case
+ * of heavy DIO or ordered reservations, preemptive flushing will just
+ * waste time and cause us to slow down.
+ */
+ ordered = percpu_counter_sum_positive(&fs_info->ordered_bytes);
+ delalloc = percpu_counter_sum_positive(&fs_info->delalloc_bytes);
+ if (ordered >= delalloc)
+ used += fs_info->delayed_refs_rsv.reserved +
+ fs_info->delayed_block_rsv.reserved;
else
- to_reclaim = 0;
- to_reclaim = min(to_reclaim, space_info->bytes_may_use +
- space_info->bytes_reserved);
- if (!to_reclaim)
- return 0;
+ used += space_info->bytes_may_use;
return (used >= thresh && !btrfs_fs_closing(fs_info) &&
!test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state));
@@ -1010,7 +1036,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
struct btrfs_block_rsv *delayed_refs_rsv;
struct btrfs_block_rsv *global_rsv;
struct btrfs_block_rsv *trans_rsv;
- u64 used;
fs_info = container_of(work, struct btrfs_fs_info,
preempt_reclaim_work);
@@ -1021,8 +1046,7 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
trans_rsv = &fs_info->trans_block_rsv;
spin_lock(&space_info->lock);
- used = btrfs_space_info_used(space_info, true);
- while (need_preemptive_reclaim(fs_info, space_info, used)) {
+ while (need_preemptive_reclaim(fs_info, space_info)) {
enum btrfs_flush_state flush;
u64 delalloc_size = 0;
u64 to_reclaim, block_rsv_size;
@@ -1084,7 +1108,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
flush_space(fs_info, space_info, to_reclaim, flush);
cond_resched();
spin_lock(&space_info->lock);
- used = btrfs_space_info_used(space_info, true);
}
spin_unlock(&space_info->lock);
}
@@ -1499,7 +1522,7 @@ static int __reserve_bytes(struct btrfs_fs_info *fs_info,
* the async reclaim as we will panic.
*/
if (!test_bit(BTRFS_FS_LOG_RECOVERING, &fs_info->flags) &&
- need_preemptive_reclaim(fs_info, space_info, used) &&
+ need_preemptive_reclaim(fs_info, space_info) &&
!work_busy(&fs_info->preempt_reclaim_work)) {
trace_btrfs_trigger_flush(fs_info, space_info->flags,
orig_bytes, flush, "preempt");
A lot of this was added all in one go with no explanation, and is a bit unwieldy and confusing. Simplify the logic to start preemptive flushing if we've reserved more than half of our available free space. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- fs/btrfs/space-info.c | 73 ++++++++++++++++++++++++++++--------------- 1 file changed, 48 insertions(+), 25 deletions(-)