3.12 compat, NUMA-aware per-superblock shrinker

Kernels >= 3.12 have a NUMA-aware superblock shrinker which is used in
ZoL by zfs_sb_prune().  This patch calls the shrinker for each on-line
NUMA node in order that memory be freed for each one.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3495

config/kernel-shrink.m4

@@ -109,3 +109,25 @@ AC_DEFUN([ZFS_AC_KERNEL_FREE_CACHED_OBJECTS], [
 		AC_MSG_RESULT(no)
 	])
 ])
+
+dnl #
+dnl # 3.12 API change
+dnl # The nid member was added to struct shrink_control to support
+dnl # NUMA-aware shrinkers.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SHRINK_CONTROL_HAS_NID], [
+	AC_MSG_CHECKING([whether shrink_control has nid])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/fs.h>
+	],[
+		struct shrink_control sc __attribute__ ((unused));
+		unsigned long scnidsize __attribute__ ((unused)) =
+		    sizeof(sc.nid);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(SHRINK_CONTROL_HAS_NID, 1,
+		    [struct shrink_control has nid])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/kernel.m4

@@ -87,6 +87,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_CALLBACK_SECURITY_INODE_INIT_SECURITY
 	ZFS_AC_KERNEL_MOUNT_NODEV
 	ZFS_AC_KERNEL_SHRINK
+	ZFS_AC_KERNEL_SHRINK_CONTROL_HAS_NID
 	ZFS_AC_KERNEL_S_INSTANCES_LIST_HEAD
 	ZFS_AC_KERNEL_S_D_OP
 	ZFS_AC_KERNEL_BDI_SETUP_AND_REGISTER

module/zfs/zfs_vfsops.c

@@ -68,7 +68,6 @@
 #include <sys/zpl.h>
 #include "zfs_comutil.h"
 
-
 /*ARGSUSED*/
 int
 zfs_sync(struct super_block *sb, int wait, cred_t *cr)
@@ -1093,7 +1092,17 @@ zfs_sb_prune(struct super_block *sb, unsigned long nr_to_scan, int *objects)
 
 	ZFS_ENTER(zsb);
 
-#if defined(HAVE_SPLIT_SHRINKER_CALLBACK)
+#if defined(HAVE_SPLIT_SHRINKER_CALLBACK) && \
+	defined(SHRINK_CONTROL_HAS_NID) && \
+	defined(SHRINKER_NUMA_AWARE)
+	if (sb->s_shrink.flags & SHRINKER_NUMA_AWARE) {
+		*objects = 0;
+		for_each_online_node(sc.nid)
+			*objects += (*shrinker->scan_objects)(shrinker, &sc);
+	} else {
+			*objects = (*shrinker->scan_objects)(shrinker, &sc);
+	}
+#elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
 	*objects = (*shrinker->scan_objects)(shrinker, &sc);
 #elif defined(HAVE_SHRINK)
 	*objects = (*shrinker->shrink)(shrinker, &sc);