Fix ARC behavior on 32-bit systems

With the addition of the ABD changes consumption of the virtual
address space has been greatly reduced.  This exposed an issue on
CONFIG_HIGHMEM systems where free memory was being calculated
incorrectly.  Functionally this didn't cause any major problems
prior to ABD because a lack of available virtual address space
was used as an indicator of low memory.

This patch makes the following changes to address the issue and
in the process realigns the code further with OpenZFS.  There
are no substantive changes in behavior for 64-bit systems.

* Added CONFIG_HIGHMEM case to the arc_all_memory() and
  arc_free_memory() functions to only consider low memory pages
  on CONFIG_HIGHMEM systems.

* The arc_free_memory() function was updated to return bytes
  instead of pages to be consistent with the other helper
  functions.  In user space we make up some reasonable values
  since currently only testing is performed in this context.

* Adds three new values to the arcstats kstat to provide visibility
  in to the ARC's assessment of the memory situation:
  memory_all_bytes, memory_free_bytes, and memory_available_bytes.

* Added kmem_reap() call to arc_available_memory() for 32-bit
  builds to realign code with OpenZFS.

* Reduced size of test file in /async_destroy_001_pos.ksh to
  speed up test case.  Multiple txgs are still required.

* Move vdevs used by zpool_clear_001_pos and zpool_upgrade_002_pos
  to TEST_BASE_DIR location to speed up test cases.

Reviewed-by: David Quigley <david.quigley@intel.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #5352
Closes #6734

tests/zfs-tests/tests/functional/cli_root/zpool_clear/zpool_clear_001_pos.ksh

@@ -50,7 +50,7 @@ function cleanup
         poolexists $TESTPOOL1 && \
                 log_must zpool destroy -f $TESTPOOL1
 
-        for file in `ls $TESTDIR/file.*`; do
+        for file in `ls $TEST_BASE_DIR/file.*`; do
 		log_must rm -f $file
         done
 }
@@ -62,12 +62,12 @@ log_onexit cleanup
 #make raw files to create various configuration pools
 typeset -i i=0
 while (( i < 3 )); do
-	log_must mkfile $FILESIZE $TESTDIR/file.$i
+	log_must truncate -s $FILESIZE $TEST_BASE_DIR/file.$i
 
 	(( i = i + 1 ))
 done
 
-fbase=$TESTDIR/file
+fbase=$TEST_BASE_DIR/file
 set -A poolconf "mirror $fbase.0 $fbase.1 $fbase.2" \
                 "raidz1 $fbase.0 $fbase.1 $fbase.2" \
                 "raidz2 $fbase.0 $fbase.1 $fbase.2"

tests/zfs-tests/tests/functional/cli_root/zpool_upgrade/zpool_upgrade.kshlib

@@ -50,9 +50,9 @@ function create_old_pool
 	for pool_file in $pool_files; do
 		log_must bzcat \
 		    $STF_SUITE/tests/functional/cli_root/zpool_upgrade/$pool_file.bz2 \
-		    >/$TESTPOOL/$pool_file
+		    >$TEST_BASE_DIR/$pool_file
 	done
-	log_must zpool import -d /$TESTPOOL $pool_name
+	log_must zpool import -d $TEST_BASE_DIR $pool_name
 
 	# Put some random contents into the pool
 	for i in {1..1024} ; do
@@ -97,7 +97,7 @@ function destroy_upgraded_pool
 		log_must zpool destroy $pool_name
 	fi
 	for file in $pool_files; do
-		rm -f /$TESTPOOL/$file
+		rm -f $TEST_BASE_DIR/$file
 	done
 }
 
@@ -112,8 +112,8 @@ function check_pool
 	typeset pool=$1
 	typeset flag=$2
 	find /$pool -type f -exec cksum {} + > \
-		/$TESTPOOL/pool-checksums.$pool.$flag
-	echo /$TESTPOOL/pool-checksums.$pool.$flag
+		$TEST_BASE_DIR/pool-checksums.$pool.$flag
+	echo $TEST_BASE_DIR/pool-checksums.$pool.$flag
 }
 
 # This function simply checks that a pool has a particular version number

tests/zfs-tests/tests/functional/cli_root/zpool_upgrade/zpool_upgrade_004_pos.ksh

@@ -78,10 +78,10 @@ for config in $CONFIGS ; do
 	typeset -n pool_name=ZPOOL_VERSION_${config}_NAME
 
 	check_pool $pool_name post > /dev/null
-	log_must diff /$TESTPOOL/pool-checksums.$pool_name.pre \
-	    /$TESTPOOL/pool-checksums.$pool_name.post
-	rm /$TESTPOOL/pool-checksums.$pool_name.pre \
-	    /$TESTPOOL/pool-checksums.$pool_name.post
+	log_must diff $TEST_BASE_DIR/pool-checksums.$pool_name.pre \
+	    $TEST_BASE_DIR/pool-checksums.$pool_name.post
+	rm $TEST_BASE_DIR/pool-checksums.$pool_name.pre \
+	    $TEST_BASE_DIR/pool-checksums.$pool_name.post
 	destroy_upgraded_pool $config
 done
 

tests/zfs-tests/tests/functional/features/async_destroy/async_destroy_001_pos.ksh

@@ -56,12 +56,9 @@ log_assert "async_destroy can suspend and resume traversal"
 
 log_must zfs create -o recordsize=512 -o compression=off $TEST_FS
 
-# Create enough blocks that it will take 4 TXGs to free them all.
-typeset zfs_free_max_blocks=100000
-typeset blocks=$((zfs_free_max_blocks * 4 * 512 / 1024 / 1024))
-
-log_must dd bs=1024k count=$blocks if=/dev/zero of=/$TEST_FS/file
-
+# Create enough blocks that it will take multiple TXGs to free them all.
+log_must dd bs=1024k count=128 if=/dev/zero of=/$TEST_FS/file
+log_must sync
 log_must zfs destroy $TEST_FS
 
 #