svn commit: r320430 - head/sys/vm

[Konstantin Belousov]

Author: kib
Date: Wed Jun 28 04:02:36 2017
New Revision: 320430
URL: https://svnweb.freebsd.org/changeset/base/320430

Log:
  Treat the addr argument for mmap(2) request without MAP_FIXED flag as
  a hint.
  
  Right now, for non-fixed mmap(2) calls, addr is de-facto interpreted
  as the absolute minimal address of the range where the mapping is
  created.  The VA allocator only allocates in the range [addr,
  VM_MAXUSER_ADDRESS].  This is too restrictive, the mmap(2) call might
  unduly fail if there is no free addresses above addr but a lot of
  usable space below it.
  
  Lift this implementation limitation by allocating VA in two passes.
  First, try to allocate above addr, as before.  If that fails, do the
  second pass with less restrictive constraints for the start of
  allocation by specifying minimal allocation address at the max bss
  end, if this limit is less than addr.
  
  One important case where this change makes a difference is the
  allocation of the stacks for new threads in libthr.  Under some
  configuration conditions, libthr tries to hint kernel to reuse the
  main thread stack grow area for the new stacks.  This cannot work by
  design now after grow area is converted to stack, and there is no
  unallocated VA above the main stack.  Interpreting requested stack
  base address as the hint provides compatibility with old libthr and
  with (mis-)configured current libthr.
  
  Reviewed by:	alc
  Tested by:	dim (previous version)
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/vm/vm_map.c
  head/sys/vm/vm_map.h
  head/sys/vm/vm_mmap.c

Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c	Wed Jun 28 04:01:29 2017	(r320429)
+++ head/sys/vm/vm_map.c	Wed Jun 28 04:02:36 2017	(r320430)
@@ -1556,6 +1556,25 @@ again:
 	return (result);
 }
 
+int
+vm_map_find_min(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
+    vm_offset_t *addr, vm_size_t length, vm_offset_t min_addr,
+    vm_offset_t max_addr, int find_space, vm_prot_t prot, vm_prot_t max,
+    int cow)
+{
+	vm_offset_t hint;
+	int rv;
+
+	hint = *addr;
+	for (;;) {
+		rv = vm_map_find(map, object, offset, addr, length, max_addr,
+		    find_space, prot, max, cow);
+		if (rv == KERN_SUCCESS || min_addr >= hint)
+			return (rv);
+		*addr = min_addr;
+	}
+}
+
 /*
  *	vm_map_simplify_entry:
  *

Modified: head/sys/vm/vm_map.h
==============================================================================
--- head/sys/vm/vm_map.h	Wed Jun 28 04:01:29 2017	(r320429)
+++ head/sys/vm/vm_map.h	Wed Jun 28 04:02:36 2017	(r320430)
@@ -372,6 +372,8 @@ vm_map_t vm_map_create(pmap_t, vm_offset_t, vm_offset_
 int vm_map_delete(vm_map_t, vm_offset_t, vm_offset_t);
 int vm_map_find(vm_map_t, vm_object_t, vm_ooffset_t, vm_offset_t *, vm_size_t,
     vm_offset_t, int, vm_prot_t, vm_prot_t, int);
+int vm_map_find_min(vm_map_t, vm_object_t, vm_ooffset_t, vm_offset_t *,
+    vm_size_t, vm_offset_t, vm_offset_t, int, vm_prot_t, vm_prot_t, int);
 int vm_map_fixed(vm_map_t, vm_object_t, vm_ooffset_t, vm_offset_t, vm_size_t,
     vm_prot_t, vm_prot_t, int);
 int vm_map_findspace (vm_map_t, vm_offset_t, vm_size_t, vm_offset_t *);

Modified: head/sys/vm/vm_mmap.c
==============================================================================
--- head/sys/vm/vm_mmap.c	Wed Jun 28 04:01:29 2017	(r320429)
+++ head/sys/vm/vm_mmap.c	Wed Jun 28 04:02:36 2017	(r320430)
@@ -1438,10 +1438,12 @@ vm_mmap_object(vm_map_t map, vm_offset_t *addr, vm_siz
     vm_prot_t maxprot, int flags, vm_object_t object, vm_ooffset_t foff,
     boolean_t writecounted, struct thread *td)
 {
-	boolean_t fitit;
+	boolean_t curmap, fitit;
+	vm_offset_t max_addr;
 	int docow, error, findspace, rv;
 
-	if (map == &td->td_proc->p_vmspace->vm_map) {
+	curmap = map == &td->td_proc->p_vmspace->vm_map;
+	if (curmap) {
 		PROC_LOCK(td->td_proc);
 		if (map->size + size > lim_cur_proc(td->td_proc, RLIMIT_VMEM)) {
 			PROC_UNLOCK(td->td_proc);
@@ -1529,11 +1531,20 @@ vm_mmap_object(vm_map_t map, vm_offset_t *addr, vm_siz
 			    MAP_ALIGNMENT_SHIFT);
 		else
 			findspace = VMFS_OPTIMAL_SPACE;
-		rv = vm_map_find(map, object, foff, addr, size,
+		max_addr = 0;
 #ifdef MAP_32BIT
-		    flags & MAP_32BIT ? MAP_32BIT_MAX_ADDR :
+		if ((flags & MAP_32BIT) != 0)
+			max_addr = MAP_32BIT_MAX_ADDR;
 #endif
-		    0, findspace, prot, maxprot, docow);
+		if (curmap) {
+			rv = vm_map_find_min(map, object, foff, addr, size,
+			    round_page((vm_offset_t)td->td_proc->p_vmspace->
+			    vm_daddr + lim_max(td, RLIMIT_DATA)), max_addr,
+			    findspace, prot, maxprot, docow);
+		} else {
+			rv = vm_map_find(map, object, foff, addr, size,
+			    max_addr, findspace, prot, maxprot, docow);
+		}
 	} else {
 		rv = vm_map_fixed(map, object, foff, *addr, size,
 		    prot, maxprot, docow);