Illumos #1862 incremental zfs receive fails for sparse file > 8PB

1862 incremental zfs receive fails for sparse file > 8PB

Reviewed by: Matt Ahrens <matthew.ahrens@delphix.com>
Reviewed by: Simon Klinkert <klinkert@webgods.de>
Approved by: Eric Schrock <eric.schrock@delphix.com>

References:
  illumos/illumos-gate@31495a1
  illumos changeset: 13789:f0c17d471b7a
  https://www.illumos.org/issues/1862

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/zfs/dmu_tx.c

@@ -446,6 +446,7 @@ dmu_tx_count_free(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
 	dsl_dataset_t *ds = dn->dn_objset->os_dsl_dataset;
 	spa_t *spa = txh->txh_tx->tx_pool->dp_spa;
 	int epbs;
+	uint64_t l0span = 0, nl1blks = 0;
 
 	if (dn->dn_nlevels == 0)
 		return;
@@ -478,6 +479,7 @@ dmu_tx_count_free(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
 			nblks = dn->dn_maxblkid - blkid;
 
 	}
+	l0span = nblks;    /* save for later use to calc level > 1 overhead */
 	if (dn->dn_nlevels == 1) {
 		int i;
 		for (i = 0; i < nblks; i++) {
@@ -490,24 +492,10 @@ dmu_tx_count_free(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
 			}
 			unref += BP_GET_ASIZE(bp);
 		}
+		nl1blks = 1;
 		nblks = 0;
 	}
 
-	/*
-	 * Add in memory requirements of higher-level indirects.
-	 * This assumes a worst-possible scenario for dn_nlevels.
-	 */
-	{
-		uint64_t blkcnt = 1 + ((nblks >> epbs) >> epbs);
-		int level = (dn->dn_nlevels > 1) ? 2 : 1;
-
-		while (level++ < DN_MAX_LEVELS) {
-			txh->txh_memory_tohold += blkcnt << dn->dn_indblkshift;
-			blkcnt = 1 + (blkcnt >> epbs);
-		}
-		ASSERT(blkcnt <= dn->dn_nblkptr);
-	}
-
 	lastblk = blkid + nblks - 1;
 	while (nblks) {
 		dmu_buf_impl_t *dbuf;
@@ -578,11 +566,35 @@ dmu_tx_count_free(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
 		}
 		dbuf_rele(dbuf, FTAG);
 
+		++nl1blks;
 		blkid += tochk;
 		nblks -= tochk;
 	}
 	rw_exit(&dn->dn_struct_rwlock);
 
+	/*
+	 * Add in memory requirements of higher-level indirects.
+	 * This assumes a worst-possible scenario for dn_nlevels and a
+	 * worst-possible distribution of l1-blocks over the region to free.
+	 */
+	{
+		uint64_t blkcnt = 1 + ((l0span >> epbs) >> epbs);
+		int level = 2;
+		/*
+		 * Here we don't use DN_MAX_LEVEL, but calculate it with the
+		 * given datablkshift and indblkshift. This makes the
+		 * difference between 19 and 8 on large files.
+		 */
+		int maxlevel = 2 + (DN_MAX_OFFSET_SHIFT - dn->dn_datablkshift) /
+		    (dn->dn_indblkshift - SPA_BLKPTRSHIFT);
+
+		while (level++ < maxlevel) {
+			txh->txh_memory_tohold += MIN(blkcnt, (nl1blks >> epbs))
+			    << dn->dn_indblkshift;
+			blkcnt = 1 + (blkcnt >> epbs);
+		}
+	}
+
 	/* account for new level 1 indirect blocks that might show up */
 	if (skipped > 0) {
 		txh->txh_fudge += skipped << dn->dn_indblkshift;