ZTS: Reduce extra caching in pool_checkpoint (#17268)

Those tests are write-mostly at the nested pool.  Considering we have
3 more layers of caching underneath, we can hint ZFS how to use the
memory better by setting primarycache=metadata.

While there, add missing zpool sync after rm in checkpoint_capacity
before we could potentially see the freed space, would not there be
a pool checkpoint.

Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
(cherry picked from commit 1ef706c4ad)

tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_capacity.ksh

@@ -60,14 +60,15 @@ log_must set_tunable32 SPA_ASIZE_INFLATION 4
 log_must zfs create $DISKFS
 
 log_must mkfile $FILEDISKSIZE $FILEDISK1
-log_must zpool create $NESTEDPOOL $FILEDISK1
+log_must zpool create -O primarycache=metadata $NESTEDPOOL $FILEDISK1
 
-log_must zfs create -o compression=lz4 -o recordsize=8k $NESTEDFS0
+log_must zfs create $NESTEDFS0
 log_must dd if=/dev/urandom of=$NESTEDFS0FILE bs=1M count=700
 FILE0INTRO=$(head -c 100 $NESTEDFS0FILE)
 
 log_must zpool checkpoint $NESTEDPOOL
 log_must rm $NESTEDFS0FILE
+log_must sync_pool $NESTEDPOOL
 
 #
 # only for debugging purposes

tests/zfs-tests/tests/functional/pool_checkpoint/pool_checkpoint.kshlib

@@ -139,7 +139,8 @@ function setup_nested_pool
 	log_must truncate -s $DISKSIZE $FILEDISK1
 	log_must truncate -s $DISKSIZE $FILEDISK2
 
-	log_must zpool create -O sync=disabled $NESTEDPOOL $FILEDISKS
+	log_must zpool create -O primarycache=metadata -O sync=disabled \
+	    $NESTEDPOOL $FILEDISKS
 }
 
 function setup_test_pool