Author: kib
Date: Mon Dec 7 11:14:57 2015
New Revision: 291934
URL: https://svnweb.freebsd.org/changeset/base/291934
Log:
MFC r290917:
Provide the OOM-specific vm_pageout_oom_pagecount() function which
estimates the amount of reclamaible memory which could be stolen if
the process is killed.
Modified:
stable/10/sys/vm/vm_pageout.c
Directory Properties:
stable/10/ (props changed)
Modified: stable/10/sys/vm/vm_pageout.c
==============================================================================
--- stable/10/sys/vm/vm_pageout.c Mon Dec 7 11:12:03 2015
(r291933)
+++ stable/10/sys/vm/vm_pageout.c Mon Dec 7 11:14:57 2015
(r291934)
@@ -1526,6 +1526,65 @@ vm_pageout_mightbe_oom(struct vm_domain
atomic_subtract_int(&vm_pageout_oom_vote, 1);
}
+/*
+ * The OOM killer is the page daemon's action of last resort when
+ * memory allocation requests have been stalled for a prolonged period
+ * of time because it cannot reclaim memory. This function computes
+ * the approximate number of physical pages that could be reclaimed if
+ * the specified address space is destroyed.
+ *
+ * Private, anonymous memory owned by the address space is the
+ * principal resource that we expect to recover after an OOM kill.
+ * Since the physical pages mapped by the address space's COW entries
+ * are typically shared pages, they are unlikely to be released and so
+ * they are not counted.
+ *
+ * To get to the point where the page daemon runs the OOM killer, its
+ * efforts to write-back vnode-backed pages may have stalled. This
+ * could be caused by a memory allocation deadlock in the write path
+ * that might be resolved by an OOM kill. Therefore, physical pages
+ * belonging to vnode-backed objects are counted, because they might
+ * be freed without being written out first if the address space holds
+ * the last reference to an unlinked vnode.
+ *
+ * Similarly, physical pages belonging to OBJT_PHYS objects are
+ * counted because the address space might hold the last reference to
+ * the object.
+ */
+static long
+vm_pageout_oom_pagecount(struct vmspace *vmspace)
+{
+ vm_map_t map;
+ vm_map_entry_t entry;
+ vm_object_t obj;
+ long res;
+
+ map = &vmspace->vm_map;
+ KASSERT(!map->system_map, ("system map"));
+ sx_assert(&map->lock, SA_LOCKED);
+ res = 0;
+ for (entry = map->header.next; entry != &map->header;
+ entry = entry->next) {
+ if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0)
+ continue;
+ obj = entry->object.vm_object;
+ if (obj == NULL)
+ continue;
+ if ((entry->eflags & MAP_ENTRY_NEEDS_COPY) != 0 &&
+ obj->ref_count != 1)
+ continue;
+ switch (obj->type) {
+ case OBJT_DEFAULT:
+ case OBJT_SWAP:
+ case OBJT_PHYS:
+ case OBJT_VNODE:
+ res += obj->resident_page_count;
+ break;
+ }
+ }
+ return (res);
+}
+
void
vm_pageout_oom(int shortage)
{
@@ -1599,12 +1658,13 @@ vm_pageout_oom(int shortage)
}
PROC_UNLOCK(p);
size = vmspace_swap_count(vm);
- vm_map_unlock_read(&vm->vm_map);
if (shortage == VM_OOM_MEM)
- size += vmspace_resident_count(vm);
+ size += vm_pageout_oom_pagecount(vm);
+ vm_map_unlock_read(&vm->vm_map);
vmspace_free(vm);
+
/*
- * if the this process is bigger than the biggest one
+ * If this process is bigger than the biggest one,
* remember it.
*/
if (size > bigsize) {
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