Illumos 4950 - files sometimes can't be removed from a full filesystem

4950 files sometimes can't be removed from a full filesystem
Reviewed by: Adam Leventhal <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: Sebastien Roy <[email protected]>
Reviewed by: Boris Protopopov <[email protected]>
Approved by: Dan McDonald <[email protected]>

References:
  https://www.illumos.org/issues/4950
  https://github.com/illumos/illumos-gate/commit/4bb7380

Porting notes:
- ZoL currently does not log discards to zvols, so the portion of
  this patch that modifies the discard logging to mark it as
  freeing space has been discarded.

2. may_delete_now had been removed from zfs_remove() in ZoL.
   It has been reintroduced.

3. We do not try to emulate vnodes, so the following lines are
   not valid on Linux:

	mutex_enter(&vp->v_lock);
	may_delete_now = vp->v_count == 1 && !vn_has_cached_data(vp);
	mutex_exit(&vp->v_lock);

  This has been replaced with:

	mutex_enter(&zp->z_lock);
	may_delete_now = atomic_read(&ip->i_count) == 1 && !(zp->z_is_mapped);
	mutex_exit(&zp->z_lock);

Ported-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 26 insertions, 0 deletions

diff --git a/module/zfs/dmu_tx.c b/module/zfs/dmu_tx.c
index 016defe79..74e323dbd 100644
--- a/module/zfs/dmu_tx.c
+++ b/module/zfs/dmu_tx.c
@@ -610,6 +610,32 @@ dmu_tx_count_free(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
 	txh->txh_space_tounref += unref;
 }
 
+/*
+ * This function marks the transaction as being a "net free".  The end
+ * result is that refquotas will be disabled for this transaction, and
+ * this transaction will be able to use half of the pool space overhead
+ * (see dsl_pool_adjustedsize()).  Therefore this function should only
+ * be called for transactions that we expect will not cause a net increase
+ * in the amount of space used (but it's OK if that is occasionally not true).
+ */
+void
+dmu_tx_mark_netfree(dmu_tx_t *tx)
+{
+	dmu_tx_hold_t *txh;
+
+	txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
+	    DMU_NEW_OBJECT, THT_FREE, 0, 0);
+
+	/*
+	 * Pretend that this operation will free 1GB of space.  This
+	 * should be large enough to cancel out the largest write.
+	 * We don't want to use something like UINT64_MAX, because that would
+	 * cause overflows when doing math with these values (e.g. in
+	 * dmu_tx_try_assign()).
+	 */
+	txh->txh_space_tofree = txh->txh_space_tounref = 1024 * 1024 * 1024;
+}
+
 void
 dmu_tx_hold_free(dmu_tx_t *tx, uint64_t object, uint64_t off, uint64_t len)
 {