Fix free memory calculation on v3.14+

Provide infrastructure to auto-configure to enum and API changes in the
global page stats used for our free memory calculations.

arc_free_memory has been broken since an API change in Linux v3.14:

2016-07-28 v4.8 599d0c95 mm, vmscan: move LRU lists to node
2016-07-28 v4.8 75ef7184 mm, vmstat: add infrastructure for per-node
  vmstats

These commits moved some of global_page_state() into
global_node_page_state(). The API change was particularly egregious as,
instead of breaking the old code, it silently did the wrong thing and we
continued using global_page_state() where we should have been using
global_node_page_state(), thus indexing into the wrong array via
NR_SLAB_RECLAIMABLE et al.

There have been further API changes along the way:

2017-07-06 v4.13 385386cf mm: vmstat: move slab statistics from zone to
  node counters
2017-09-06 v4.14 c41f012a mm: rename global_page_state to
  global_zone_page_state

...and various (incomplete, as it turns out) attempts to accomodate
these changes in ZoL:

2017-08-24 2209e40 Linux 4.8+ compatibility fix for vm stats
2017-09-16 787acae Linux 3.14 compat: IO acct, global_page_state, etc
2017-09-19 661907e Linux 4.14 compat: IO acct, global_page_state, etc

The config infrastructure provided here resolves these issues going back
to the original API change in v3.14 and is robust against further Linux
changes in this area.

Signed-off-by: Chris Dunlop <chris@onthe.net.au>

config/kernel-global_page_state.m4

@@ -0,0 +1,72 @@
+dnl #
+dnl # 4.8 API change
+dnl # kernel vm counters change
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_GLOBAL_NODE_PAGE_STATE], [
+	AC_MSG_CHECKING([whether to use vm_node_stat based fn's])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/mm.h>
+		#include <linux/vmstat.h>
+	],[
+			int a __attribute__ ((unused)) = NR_VM_NODE_STAT_ITEMS;
+			long x __attribute__ ((unused)) =
+				atomic_long_read(&vm_node_stat[0]);
+			(void) global_node_page_state(0);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(ZFS_GLOBAL_NODE_PAGE_STATE, 1,
+			[using global_node_page_state()])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+dnl #
+dnl # 4.14 API change (c41f012ade)
+dnl # mm: rename global_page_state to global_zone_page_state
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_GLOBAL_ZONE_PAGE_STATE], [
+	AC_MSG_CHECKING([whether to use global_zone_page_state])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/mm.h>
+		#include <linux/vmstat.h>
+	],[
+			(void) global_zone_page_state(0);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(ZFS_GLOBAL_ZONE_PAGE_STATE, 1,
+			[using global_zone_page_state()])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+dnl #
+dnl # Create a define for an enum member
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_ENUM_MEMBER], [
+	AS_IF(
+		[AC_TRY_COMMAND(scripts/enum-extract.pl $2 $3 | egrep -x $1)],
+		[
+			AC_MSG_RESULT([yes])
+			AC_DEFINE(m4_join([_], [ZFS_ENUM], m4_toupper($2), $1), 1, [enum $2 has $1])
+		],
+		[AC_MSG_RESULT([no])]
+	)
+])
+
+dnl #
+dnl # enum members in which we're interested
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_GLOBAL_PAGE_STATE], [
+	ZFS_AC_KERNEL_GLOBAL_NODE_PAGE_STATE
+	ZFS_AC_KERNEL_GLOBAL_ZONE_PAGE_STATE
+
+	ZFS_AC_KERNEL_ENUM_MEMBER([NR_INACTIVE_ANON],      [node_stat_item], [$LINUX/include/linux/mmzone.h])
+	ZFS_AC_KERNEL_ENUM_MEMBER([NR_INACTIVE_FILE],      [node_stat_item], [$LINUX/include/linux/mmzone.h])
+	ZFS_AC_KERNEL_ENUM_MEMBER([NR_SLAB_RECLAIMABLE],   [node_stat_item], [$LINUX/include/linux/mmzone.h])
+
+	ZFS_AC_KERNEL_ENUM_MEMBER([NR_INACTIVE_ANON],      [zone_stat_item], [$LINUX/include/linux/mmzone.h])
+	ZFS_AC_KERNEL_ENUM_MEMBER([NR_INACTIVE_FILE],      [zone_stat_item], [$LINUX/include/linux/mmzone.h])
+	ZFS_AC_KERNEL_ENUM_MEMBER([NR_SLAB_RECLAIMABLE],   [zone_stat_item], [$LINUX/include/linux/mmzone.h])
+])

config/kernel.m4

@@ -123,7 +123,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_RENAME_WANTS_FLAGS
 	ZFS_AC_KERNEL_HAVE_GENERIC_SETXATTR
 	ZFS_AC_KERNEL_CURRENT_TIME
-	ZFS_AC_KERNEL_VM_NODE_STAT
+	ZFS_AC_KERNEL_GLOBAL_PAGE_STATE
 
 	AS_IF([test "$LINUX_OBJ" != "$LINUX"], [
 		KERNEL_MAKE="$KERNEL_MAKE O=$LINUX_OBJ"

include/linux/mm_compat_zfs.h

@@ -0,0 +1,92 @@
+#ifndef	_ZFS_MM_COMPAT_ZFS_H
+#define	_ZFS_MM_COMPAT_ZFS_H
+
+/*
+ * We have various enum members moving between two separate enum types,
+ * and accessed by different functions at various times. Centralise the
+ * insanity.
+ *
+ * < v4.8: all enums in zone_stat_item, via global_page_state()
+ * v4.8: some enums moved to node_stat_item, global_node_page_state() introduced
+ * v4.13: some enums moved from zone_stat_item to node_state_item
+ * v4.14: global_page_state() rename to global_zone_page_state()
+ */
+
+/*
+ * Ensure the config tests are finding one and only one of each enum of interest
+ */
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_ANON) && \
+	defined(ZFS_ENUM_ZONE_STAT_ITEM_NR_INACTIVE_ANON)
+#error NR_INACTIVE_ANON defined in both node_stat_item and zone_stat_item
+#elif	! defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_ANON) && \
+	! defined(ZFS_ENUM_ZONE_STAT_ITEM_NR_INACTIVE_ANON)
+#error NR_INACTIVE_ANON not found in either node_stat_item and zone_stat_item
+#endif
+
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_FILE) && \
+	defined(ZFS_ENUM_ZONE_STAT_ITEM_NR_INACTIVE_FILE)
+#error NR_INACTIVE_FILE defined in both node_stat_item and zone_stat_item
+#elif	! defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_FILE) && \
+	! defined(ZFS_ENUM_ZONE_STAT_ITEM_NR_INACTIVE_FILE)
+#error NR_INACTIVE_FILE not found in either node_stat_item and zone_stat_item
+#endif
+
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_SLAB_RECLAIMABLE) && \
+	defined(ZFS_ENUM_ZONE_STAT_ITEM_NR_SLAB_RECLAIMABLE)
+#error NR_SLAB_RECLAIMABLE defined in both node_stat_item and zone_stat_item
+#elif	! defined(ZFS_ENUM_NODE_STAT_ITEM_NR_SLAB_RECLAIMABLE) && \
+	! defined(ZFS_ENUM_ZONE_STAT_ITEM_NR_SLAB_RECLAIMABLE)
+#error NR_SLAB_RECLAIMABLE not found in either node_stat_item and zone_stat_item
+#endif
+
+/*
+ * Create our own accessor functions to follow the Linux API changes
+ */
+#if	defined(ZFS_GLOBAL_ZONE_PAGE_STATE)
+
+/* global_zone_page_state() introduced */
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_ANON)
+#define	nr_inactive_anon_pages() global_node_page_state(NR_INACTIVE_ANON)
+#else
+#define	nr_inactive_anon_pages() global_zone_page_state(NR_INACTIVE_ANON)
+#endif
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_FILE)
+#define	nr_inactive_file_pages() global_node_page_state(NR_INACTIVE_FILE)
+#else
+#define	nr_inactive_file_pages() global_zone_page_state(NR_INACTIVE_FILE)
+#endif
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_SLAB_RECLAIMABLE)
+#define	nr_slab_reclaimable_pages() global_node_page_state(NR_SLAB_RECLAIMABLE)
+#else
+#define	nr_slab_reclaimable_pages() global_zone_page_state(NR_SLAB_RECLAIMABLE)
+#endif
+
+#elif	defined(ZFS_GLOBAL_NODE_PAGE_STATE)
+
+/* global_node_page_state() introduced */
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_ANON)
+#define	nr_inactive_anon_pages() global_node_page_state(NR_INACTIVE_ANON)
+#else
+#define	nr_inactive_anon_pages() global_page_state(NR_INACTIVE_ANON)
+#endif
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_INACTIVE_FILE)
+#define	nr_inactive_file_pages() global_node_page_state(NR_INACTIVE_FILE)
+#else
+#define	nr_inactive_file_pages() global_page_state(NR_INACTIVE_FILE)
+#endif
+#if	defined(ZFS_ENUM_NODE_STAT_ITEM_NR_SLAB_RECLAIMABLE)
+#define	nr_slab_reclaimable_pages() global_node_page_state(NR_SLAB_RECLAIMABLE)
+#else
+#define	nr_slab_reclaimable_pages() global_page_state(NR_SLAB_RECLAIMABLE)
+#endif
+
+#else
+
+/* global_page_zone() only */
+#define	nr_inactive_anon_pages()    global_page_state(NR_INACTIVE_ANON)
+#define	nr_inactive_file_pages()    global_page_state(NR_INACTIVE_FILE)
+#define	nr_slab_reclaimable_pages() global_page_state(NR_SLAB_RECLAIMABLE)
+
+#endif /* ZFS_GLOBAL_ZONE_PAGE_STATE */
+
+#endif /* _ZFS_MM_COMPAT_ZFS_H */

module/zfs/arc.c

@@ -297,6 +297,7 @@
 #include <sys/fs/swapnode.h>
 #include <sys/zpl.h>
 #include <linux/mm_compat.h>
+#include <linux/mm_compat_zfs.h>
 #endif
 #include <sys/callb.h>
 #include <sys/kstat.h>
@@ -4698,18 +4699,12 @@ arc_free_memory(void)
 	struct sysinfo si;
 	si_meminfo(&si);
 	return (ptob(si.freeram - si.freehigh));
-#else
-#ifdef ZFS_GLOBAL_NODE_PAGE_STATE
-	return (ptob(nr_free_pages() +
-	    global_node_page_state(NR_INACTIVE_FILE) +
-	    global_node_page_state(NR_INACTIVE_ANON) +
-	    global_node_page_state(NR_SLAB_RECLAIMABLE)));
 #else
 	return (ptob(nr_free_pages() +
-	    global_page_state(NR_INACTIVE_FILE) +
-	    global_page_state(NR_INACTIVE_ANON) +
-	    global_page_state(NR_SLAB_RECLAIMABLE)));
-#endif /* ZFS_GLOBAL_NODE_PAGE_STATE */
+	    nr_inactive_file_pages() +
+	    nr_inactive_anon_pages() +
+	    nr_slab_reclaimable_pages()));
+
 #endif /* CONFIG_HIGHMEM */
 #else
 	return (spa_get_random(arc_all_memory() * 20 / 100));

scripts/enum-extract.pl

@@ -0,0 +1,58 @@
+#!/usr/bin/perl -w
+
+my $usage = <<EOT;
+usage: config-enum enum [file ...]
+
+Returns the elements from an enum declaration.
+
+"Best effort": we're not building an entire C interpreter here!
+EOT
+
+use warnings;
+use strict;
+use Getopt::Std;
+
+my %opts;
+
+if (!getopts("", \%opts) || @ARGV < 1) {
+	print $usage;
+	exit 2;
+}
+
+my $enum = shift;
+
+my $in_enum = 0;
+
+while (<>) {
+	# comments
+	s/\/\*.*\*\///;
+	if (m/\/\*/) {
+		while ($_ .= <>) {
+			last if s/\/\*.*\*\///s;
+		}
+	}
+
+	# preprocessor stuff
+	next if /^#/;
+
+	# find our enum
+	$in_enum = 1 if s/^\s*enum\s+${enum}(?:\s|$)//;
+	next unless $in_enum;
+
+	# remove explicit values
+	s/\s*=[^,]+,/,/g;
+
+	# extract each identifier
+	while (m/\b([a-z_][a-z0-9_]*)\b/ig) {
+		print $1, "\n";
+	}
+
+	#
+	# don't exit: there may be multiple versions of the same enum, e.g.
+	# inside different #ifdef blocks. Let's explicitly return all of
+	# them and let external tooling deal with it.
+	#
+	$in_enum = 0 if m/}\s*;/;
+}
+
+exit 0;