Use sf_buf_alloc() instead of vm_map_find() on exec_map to create the

ephemeral mappings that are used as the source for three copy
operations from kernel space to user space.  There are two reasons for
making this change: (1) Under heavy load exec_map can fill up causing
vm_map_find() to fail.  When it fails, the nascent process is aborted
(SIGABRT).  Whereas, this reimplementation using sf_buf_alloc()
sleeps.  (2) Although it is possible to sleep on vm_map_find()'s
failure until address space becomes available (see kmem_alloc_wait()),
using sf_buf_alloc() is faster.  Furthermore, the reimplementation
uses a CPU private mapping, avoiding a TLB shootdown on
multiprocessors.

Problem uncovered by: kris@
Reviewed by: tegge@
MFC after: 3 weeks

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/vm/vm_extern.h b/sys/vm/vm_extern.h
index 4fc8275..08dba00 100644
--- a/sys/vm/vm_extern.h
+++ b/sys/vm/vm_extern.h
@@ -86,6 +86,8 @@ void vsunlock(void *, size_t);
 void vm_object_print(/* db_expr_t */ long, boolean_t, /* db_expr_t */ long,
 			  char *);
 int vm_fault_quick(caddr_t v, int prot);
+struct sf_buf *vm_imgact_map_page(vm_object_t object, vm_ooffset_t offset);
+void vm_imgact_unmap_page(struct sf_buf *sf);
 void vm_thread_dispose(struct thread *td);
 void vm_thread_dispose_altkstack(struct thread *td);
 void vm_thread_new(struct thread *td, int pages);