Memory allocation spamming the system

[mcr-ksh]

txg_sync is consuming most of the CPU:
5483 root 0 -20 0 0 0 D 95 0.0 2:22.98 txg_sync

kernel oops
[ 375.167381] SPL: Showing stack for process 5483
[ 375.167381] Pid: 5483, comm: txg_sync Tainted: P W 2.6.32.27 #31
[ 375.167381] Call Trace:
[ 375.167381] [] spl_debug_dumpstack+0x2b/0x2d [spl]
[ 375.167381] [] sanitize_flags+0x73/0x84 [spl]
[ 375.167381] [] kmalloc_nofail+0x21/0x3e [spl]
[ 375.167381] [] kmem_alloc_debug+0x15d/0x2cb [spl]
[ 375.167381] [] zap_leaf_array_match+0x5b/0x191 [zfs]
[ 375.167381] [] zap_leaf_lookup+0x95/0x106 [zfs]
[ 375.167381] [] fzap_remove+0x42/0x7c [zfs]
[ 375.167381] [] zap_remove_uint64+0x6a/0x8c [zfs]
[ 375.167381] [] ddt_zap_remove+0x11/0x13 [zfs]
[ 375.167381] [] ddt_sync+0x26c/0x73b [zfs]
[ 375.167381] [] ? xen_clocksource_read+0x21/0x23
[ 375.167381] [] ? ktime_get_ts+0xad/0xba
[ 375.167381] [] dsl_scan_sync+0x237/0x7e2 [zfs]
[ 375.167381] [] ? xen_restore_fl_direct_end+0x0/0x1
[ 375.167381] [] ? spl_kmem_cache_free+0x33d/0x3a3 [spl]
[ 375.167381] [] spa_sync+0x535/0x858 [zfs]
[ 375.167381] [] txg_sync_thread+0x2a6/0x412 [zfs]
[ 375.167381] [] ? set_user_nice+0xf3/0x117
[ 375.167381] [] ? txg_sync_thread+0x0/0x412 [zfs]
[ 375.167381] [] thread_generic_wrapper+0x5c/0x66 [spl]
[ 375.167381] [] ? thread_generic_wrapper+0x0/0x66 [spl]
[ 375.167381] [] kthread+0x7a/0x82
[ 375.167381] [] child_rip+0xa/0x20
[ 375.167381] [] ? int_ret_from_sys_call+0x7/0x1b
[ 375.167381] [] ? retint_restore_args+0x5/0x6
[ 375.167381] [] ? child_rip+0x0/0x20

[behlendorf]

Closing as another instance of openzfs/zfs#917 , we'll merge a patch for this.