Improve the way to calculate available pages in tmpfs:

 - Don't deduct wired pages from total usable counts because it does not
   make any sense.  To make things worse, on systems where swap size is
   smaller than physical memory and use a lot of wired pages (e.g. ZFS),
   tmpfs can suddenly have free space of 0 because of this;
 - Count cached pages as available; [1]
 - Don't count inactive pages as available, technically we could but that
   might be too aggressive; [1]

[1] Suggested by kib@

MFC after:	1 week

1 files changed, 1 insertions, 4 deletions

diff --git a/sys/fs/tmpfs/tmpfs.h b/sys/fs/tmpfs/tmpfs.h
index e95e3c80f6f7..fe00fea0c91c 100644
--- a/sys/fs/tmpfs/tmpfs.h
+++ b/sys/fs/tmpfs/tmpfs.h
@@ -502,11 +502,8 @@ int	tmpfs_truncate(struct vnode *, off_t);
 static __inline size_t
 tmpfs_mem_info(void)
 {
-	size_t size;
 
-	size = swap_pager_avail + cnt.v_free_count + cnt.v_inactive_count;
-	size -= size > cnt.v_wire_count ? cnt.v_wire_count : size;
-	return size;
+	return (swap_pager_avail + cnt.v_free_count + cnt.v_cache_count);
 }
 
 /* Returns the maximum size allowed for a tmpfs file system.  This macro