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 

1 files changed, 6 insertions, 17 deletions

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index a78a029c2..c6ff6171c 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -297,6 +297,7 @@
 #include <sys/fs/swapnode.h>
 #include <sys/zpl.h>
 #include <linux/mm_compat.h>
+#include <linux/page_compat.h>
 #endif
 #include <sys/callb.h>
 #include <sys/kstat.h>
@@ -4699,17 +4700,11 @@ arc_free_memory(void)
 	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));
@@ -5121,13 +5116,7 @@ arc_evictable_memory(void)
 	 * Scale reported evictable memory in proportion to page cache, cap
 	 * at specified min/max.
 	 */
-#ifdef ZFS_GLOBAL_NODE_PAGE_STATE
-	uint64_t min = (ptob(global_node_page_state(NR_FILE_PAGES)) / 100) *
-	    zfs_arc_pc_percent;
-#else
-	uint64_t min = (ptob(global_page_state(NR_FILE_PAGES)) / 100) *
-	    zfs_arc_pc_percent;
-#endif
+	uint64_t min = (ptob(nr_file_pages()) / 100) * zfs_arc_pc_percent;
 	min = MAX(arc_c_min, MIN(arc_c_max, min));
 
 	if (arc_dirty >= min)