Unlock uvm a tiny bit more

[Mark Kettenis]

This changes uvm_unmap_detach() to get rid of the "easy" entries first
before grabbing the kernel lock.  Probably doesn't help much with the
lock contention, but it avoids a locking problem that happens with
pools that use kernel_map() to allocate the kva for their pages.

ok?


Index: uvm/uvm_map.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_map.c,v
retrieving revision 1.243
diff -u -p -r1.243 uvm_map.c
--- uvm/uvm_map.c       23 Apr 2019 13:35:12 -0000      1.243
+++ uvm/uvm_map.c       13 May 2019 22:09:26 -0000
@@ -1538,8 +1538,18 @@ uvm_mapent_tryjoin(struct vm_map *map, s
 void
 uvm_unmap_detach(struct uvm_map_deadq *deadq, int flags)
 {
-       struct vm_map_entry *entry;
+       struct vm_map_entry *entry, *tmp;
        int waitok = flags & UVM_PLA_WAITOK;
+
+       TAILQ_FOREACH_SAFE(entry, deadq, dfree.deadq, tmp) {
+               /* Skip entries for which we have to grab the kernel lock. */
+               if (entry->aref.ar_amap || UVM_ET_ISSUBMAP(entry) ||
+                   UVM_ET_ISOBJ(entry))
+                       continue;
+
+               TAILQ_REMOVE(deadq, entry, dfree.deadq);
+               uvm_mapent_free(entry);
+       }
 
        if (TAILQ_EMPTY(deadq))
                return;