Linux 4.6 compat: Fall back to d_prune_aliases() if necessary

As of 4.6, the icache and dcache LRUs are memcg aware insofar as the kernel's per-superblock shrinker is concerned. The effect is that dcache or icache entries added by a task in a non-root memcg won't be scanned by the shrinker in the context of the root (or NULL) memcg. This defeats the attempts by zfs_sb_prune() to unpin buffers and can allow metadata to grow uncontrollably. This patch reverts to the d_prune_aliaes() method in case the kernel's per-superblock shrinker is not able to free anything. Signed-off-by: Tim Chase <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Signed-off-by: Chunwei Chen <[email protected]> Closes: openzfs#4726
DeHackEd · Oct 29, 2016 · 4c4df32 · 4c4df32
1 parent 5c7c5df
commit 4c4df32
Showing 1 changed file with 15 additions and 2 deletions.
diff --git a/module/zfs/zfs_vfsops.c b/module/zfs/zfs_vfsops.c
@@ -1050,8 +1050,7 @@ zfs_root(zfs_sb_t *zsb, struct inode **ipp)
 }
 EXPORT_SYMBOL(zfs_root);
 
-#if !defined(HAVE_SPLIT_SHRINKER_CALLBACK) && !defined(HAVE_SHRINK) && \
-	defined(HAVE_D_PRUNE_ALIASES)
+#ifdef HAVE_D_PRUNE_ALIASES
 /*
  * Linux kernels older than 3.1 do not support a per-filesystem shrinker.
  * To accommodate this we must improvise and manually walk the list of znodes
@@ -1141,15 +1140,29 @@ zfs_sb_prune(struct super_block *sb, unsigned long nr_to_scan, int *objects)
 	} 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);
 #elif defined(HAVE_D_PRUNE_ALIASES)
+#define	D_PRUNE_ALIASES_IS_DEFAULT
 	*objects = zfs_sb_prune_aliases(zsb, nr_to_scan);
 #else
 #error "No available dentry and inode cache pruning mechanism."
 #endif
+
+#if defined(HAVE_D_PRUNE_ALIASES) && !defined(D_PRUNE_ALIASES_IS_DEFAULT)
+#undef	D_PRUNE_ALIASES_IS_DEFAULT
+	/*
+	 * Fall back to zfs_sb_prune_aliases if the kernel's per-superblock
+	 * shrinker couldn't free anything, possibly due to the inodes being
+	 * allocated in a different memcg.
+	 */
+	if (*objects == 0)
+		*objects = zfs_sb_prune_aliases(zsb, nr_to_scan);
+#endif
+
 	ZFS_EXIT(zsb);
 
 	dprintf_ds(zsb->z_os->os_dsl_dataset,