ZTS: checkpoint_discard_busy does not set 16M on cleanup

[tsoome]

Originally hex value is used as decimal.

Motivation and Context

Description

Use correct decimal value for 16M.

How Has This Been Tested?

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• [ x] My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• [ x] I have read the contributing document.
• I have added tests to cover my changes.
• [ x] I have run the ZFS Test Suite with this change applied.
• [ x] All commit messages are properly formatted and contain Signed-off-by.

[amotin]

Better than nothing, but it would be better to restore the original value, as done by many other tests for other tunables, or even by zpool_wait_discard.ksh for this one.

[tonyhutter]

@tsoome amotin is correct - may I suggest (untested):

diff --git a/tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_discard_busy.ksh b/tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_discard_busy.ksh
index 087aef902..58eb6e969 100755
--- a/tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_discard_busy.ksh
+++ b/tests/zfs-tests/tests/functional/pool_checkpoint/checkpoint_discard_busy.ksh
@@ -42,8 +42,7 @@ log_unsupported "Skipping, issue https://github.com/openzfs/zfs/issues/12053"
 
 function test_cleanup
 {
-       # reset memory limit to 16M
-       set_tunable64 SPA_DISCARD_MEMORY_LIMIT 1000000
+       restore_tunable SPA_DISCARD_MEMORY_LIMIT
        cleanup_nested_pools
 }
 
@@ -69,6 +68,7 @@ log_onexit test_cleanup
 #      map, we should have even more time to
 #      verify this.
 #
+log_must save_tunable SPA_DISCARD_MEMORY_LIMIT
 set_tunable64 SPA_DISCARD_MEMORY_LIMIT 128
 
 log_must zpool checkpoint $NESTEDPOOL
@@ -102,7 +102,7 @@ log_mustnot zpool remove $NESTEDPOOL $FILEDISK1
 log_mustnot zpool reguid $NESTEDPOOL
 
 # reset memory limit to 16M
-set_tunable64 SPA_DISCARD_MEMORY_LIMIT 16777216
+restore_tunable SPA_DISCARD_MEMORY_LIMIT
 
 nested_wait_discard_finish
 

[behlendorf]

I'm going to go ahead and merge this as is. We can follow up with the nicer fix which preserves and restores the value.