linuxkpi: Add some basic swap functions

These are used by kms-drm to determine various heuristics relate
memory conditions.

The number of free swap pages is just a variable, and it can be
much cheaper by either adding a new getter, or simply extern'ing
swap_total. However, this patch opts to use the more expensive,
existing interface - since this isn't an operation in a high per
path.

This allows us to remove some more gpl linuxkpi and do the follo
kms-drm:
git rm linuxkpi/gplv2/include/linux/swap.h

Reviewed by:    mmacy, Johannes Lundberg <johalun0@gmail.com>
Approved by:    emaste (mentor)
Differential Revision:  https://reviews.freebsd.org/D18052

sys/compat/linuxkpi/common/include/linux/swap.h

@@ -0,0 +1,102 @@
+/*-
+ * Copyright (c) 2018 Intel Corporation
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef	_LINUX_SWAP_H_
+#define	_LINUX_SWAP_H_
+
+#include <vm/swap_pager.h>
+#include <vm/vm_pageout.h>
+
+static inline long
+get_nr_swap_pages(void)
+{
+	int i, j;
+
+	/* NB: This could be done cheaply by obtaining swap_total directly */
+	swap_pager_status(&i, &j);
+	return i - j;
+}
+
+static inline int
+current_is_kswapd(void)
+{
+	return vm_curproc_is_vmproc();
+}
+
+#endif
+/*-
+ * Copyright (c) 2018 Intel Corporation
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef	_LINUX_SWAP_H_
+#define	_LINUX_SWAP_H_
+
+#include <vm/swap_pager.h>
+#include <vm/vm_pageout.h>
+
+static inline long
+get_nr_swap_pages(void)
+{
+	int i, j;
+
+	/* NB: This could be done cheaply by obtaining swap_total directly */
+	swap_pager_status(&i, &j);
+	return i - j;
+}
+
+static inline int
+current_is_kswapd(void)
+{
+	return vm_curproc_is_vmproc();
+}
+
+#endif

sys/vm/vm_pageout.h

@@ -106,5 +106,8 @@ void vm_pageout_oom(int shortage);
 
 void vm_swapout_run(void);
 void vm_swapout_run_idle(void);
+
+bool vm_curproc_is_vmproc(void);
+
 #endif /* _KERNEL */
 #endif	/* _VM_VM_PAGEOUT_H_ */

sys/vm/vm_swapout.c

@@ -961,3 +961,10 @@ swapout(struct proc *p)
 	p->p_swtick = ticks;
 	return (0);
 }
+
+/* Used to determine if the current process is itself the reaper. */
+bool
+vm_curproc_is_vmproc(void)
+{
+	return curproc == vmproc;
+}