Lots of "malloc(M_WAITOK) of "16", forcing M_NOWAIT with ..." warnings

With GENERIC HEAD from Mar 18 15:56 UTC I get lots of :

malloc(M_WAITOK) of "16", forcing M_NOWAIT with the following non-sleepable locks held:
exclusive sleep mutex UMA lock r = 0 (0xc096c540) locked _at_ vm/uma_core.c:1498
KDB: stack backtrace:
kdb_backtrace(1,1,1,10,c10522c0) at kdb_backtrace+0x29
witness_warn(5,0,c084c567,c081642a,c146e8a0) at witness_warn+0x19a
uma_zalloc_arg(c10522c0,0,102) at uma_zalloc_arg+0x41
malloc(10,c08984c0,102,2,cf7f2000) at malloc+0xae
free_unr(c15164c0,18826,c21ea000,c1ef32c0,c2053ae0) at free_unr+0x1b
thread_fini(c21ea000,16c) at thread_fini+0x33
zone_drain(c103e2c0) at zone_drain+0x170
zone_foreach(c0763e6c,cc9bccfc,c0775821,c08344e4,246) at zone_foreach+0x37
uma_reclaim(c08344e4,246,0,cc9bcc90,c060e719) at uma_reclaim+0x12
vm_pageout_scan(0,c096cc00,0,c084e636,5c3) at vm_pageout_scan+0x101
vm_pageout(0,cc9bcd48,0,c07765e8,0) at vm_pageout+0x2c3
fork_exit(c07765e8,0,cc9bcd48) at fork_exit+0xa4
fork_trampoline() at fork_trampoline+0x8
--- trap 0x1, eip = 0, esp = 0xcc9bcd7c, ebp = 0 ---

-- 
Peter Holm