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 2209e409 Linux 4.8+ compatibility fix for vm stats
2017-09-16 787acae0 Linux 3.14 compat: IO acct, global_page_state, etc
2017-09-19 661907e6 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.

Reviewed-by: Giuseppe Di Natale <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: George Melikov <[email protected]>
Signed-off-by: Chris Dunlop <[email protected]>
Closes #7170 

2 files changed, 80 insertions, 1 deletions

diff --git a/include/linux/Makefile.am b/include/linux/Makefile.am
index 9bb0b3493..89c2689f6 100644
--- a/include/linux/Makefile.am
+++ b/include/linux/Makefile.am
@@ -9,7 +9,8 @@ KERNEL_H = \
 	$(top_srcdir)/include/linux/kmap_compat.h \
 	$(top_srcdir)/include/linux/simd_x86.h \
 	$(top_srcdir)/include/linux/simd_aarch64.h \
-	$(top_srcdir)/include/linux/mod_compat.h
+	$(top_srcdir)/include/linux/mod_compat.h \
+	$(top_srcdir)/include/linux/page_compat.h
 
 USER_H =
 
diff --git a/include/linux/page_compat.h b/include/linux/page_compat.h
new file mode 100644
index 000000000..95acb7d53
--- /dev/null
+++ b/include/linux/page_compat.h
@@ -0,0 +1,78 @@
+#ifndef	_ZFS_PAGE_COMPAT_H
+#define	_ZFS_PAGE_COMPAT_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()
+ *
+ * The defines used here are created by config/kernel-global_page_state.m4
+ */
+
+/*
+ * 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_FILE_PAGES)
+#define	nr_file_pages() global_node_page_state(NR_FILE_PAGES)
+#else
+#define	nr_file_pages() global_zone_page_state(NR_FILE_PAGES)
+#endif
+#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_FILE_PAGES)
+#define	nr_file_pages() global_node_page_state(NR_FILE_PAGES)
+#else
+#define	nr_file_pages() global_page_state(NR_FILE_PAGES)
+#endif
+#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_state() only */
+#define	nr_file_pages()			global_page_state(NR_FILE_PAGES)
+#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_PAGE_COMPAT_H */