[RFC PATCH v5 16/16] dcache: Add CONFIG_DCACHE_SMO

["Tobin C. Harding" <tobin@kernel.org>]

In an attempt to make the SMO patchset as non-invasive as possible add a
config option CONFIG_DCACHE_SMO (under "Memory Management options") for
enabling SMO for the DCACHE.  Whithout this option dcache constructor is
used but no other code is built in, with this option enabled slab
mobility is enabled and the isolate/migrate functions are built in.

Add CONFIG_DCACHE_SMO to guard the partial shrinking of the dcache via
Slab Movable Objects infrastructure.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 fs/dcache.c | 4 ++++
 mm/Kconfig  | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 0dfe580c2d42..96063e872366 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3072,6 +3072,7 @@ void d_tmpfile(struct dentry *dentry, struct inode *inode)
 }
 EXPORT_SYMBOL(d_tmpfile);
 
+#ifdef CONFIG_DCACHE_SMO
 /*
  * d_isolate() - Dentry isolation callback function.
  * @s: The dentry cache.
@@ -3144,6 +3145,7 @@ static void d_partial_shrink(struct kmem_cache *s, void **_unused, int __unused,
 
 	kfree(private);
 }
+#endif	/* CONFIG_DCACHE_SMO */
 
 static __initdata unsigned long dhash_entries;
 static int __init set_dhash_entries(char *str)
@@ -3190,7 +3192,9 @@ static void __init dcache_init(void)
 					   sizeof_field(struct dentry, d_iname),
 					   dcache_ctor);
 
+#ifdef CONFIG_DCACHE_SMO
 	kmem_cache_setup_mobility(dentry_cache, d_isolate, d_partial_shrink);
+#endif
 
 	/* Hash may have been set up in dcache_init_early */
 	if (!hashdist)
diff --git a/mm/Kconfig b/mm/Kconfig
index aa8d60e69a01..7dcea76e5ecc 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -265,6 +265,13 @@ config SMO_NODE
        help
          On NUMA systems enable moving objects to and from a specified node.
 
+config DCACHE_SMO
+       bool "Enable Slab Movable Objects for the dcache"
+       depends on SLUB
+       help
+         Under memory pressure we can try to free dentry slab cache objects from
+         the partial slab list if this is enabled.
+
 config PHYS_ADDR_T_64BIT
 	def_bool 64BIT
 
-- 
2.21.0