Linux 5.0 compat: Use totalhigh_pages()

Linux kernel commit ca79b0c211af63fa3276f0e3fd7dd9ada2439839
"mm: convert totalram_pages and totalhigh_pages variables to atomic"

replaced `totalhigh_pages` with an inline function `totalhigh_pages()`.
This broke compilation on IA32, etc, as ZoL uses `totalhigh_pages`
on archs with highmem. Confirmed on Fedora 30 (5.0.9-301.fc30.i686).

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Closes openzfs#8677
Closes openzfs#8701

config/kernel-totalhigh_pages.m4

@@ -0,0 +1,19 @@
+dnl #
+dnl # 5.0 API change
+dnl #
+dnl # ca79b0c211af mm: convert totalram_pages and totalhigh_pages variables to atomic
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_TOTALHIGH_PAGES], [
+	AC_MSG_CHECKING([whether totalhigh_pages() exists])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/highmem.h>
+	],[
+		unsigned long pages __attribute__ ((unused));
+		pages = totalhigh_pages();
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_TOTALHIGH_PAGES, 1, [totalhigh_pages() exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/kernel.m4

@@ -164,6 +164,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_IN_COMPAT_SYSCALL
 	ZFS_AC_KERNEL_KTIME_GET_COARSE_REAL_TS64
 	ZFS_AC_KERNEL_TOTALRAM_PAGES_FUNC
+	ZFS_AC_KERNEL_TOTALHIGH_PAGES
 	ZFS_AC_KERNEL_BLK_QUEUE_DISCARD
 	ZFS_AC_KERNEL_BLK_QUEUE_SECURE_ERASE
 

include/spl/sys/vmsystm.h

@@ -39,6 +39,12 @@
 #define	zfs_totalram_pages	totalram_pages
 #endif
 
+#ifdef HAVE_TOTALHIGH_PAGES
+#define	zfs_totalhigh_pages	totalhigh_pages()
+#else
+#define	zfs_totalhigh_pages	totalhigh_pages
+#endif
+
 #define	membar_producer()		smp_wmb()
 #define	physmem				zfs_totalram_pages
 #define	freemem			(nr_free_pages() + \

module/zfs/arc.c

@@ -4828,7 +4828,7 @@ arc_all_memory(void)
 {
 #ifdef _KERNEL
 #ifdef CONFIG_HIGHMEM
-	return (ptob(zfs_totalram_pages - totalhigh_pages));
+	return (ptob(zfs_totalram_pages - zfs_totalhigh_pages));
 #else
 	return (ptob(zfs_totalram_pages));
 #endif /* CONFIG_HIGHMEM */