[RFC PATCH v5 00/16] Slab Movable Objects (SMO)

[RFC PATCH v5 00/16] Slab Movable Objects (SMO)

[Tobin C. Harding]

Hi,

Another iteration of the SMO patch set, updates to this version are
restricted to the XArray patches (#9 and #10 and tested with module
implemented in #11).

Applies on top of Linus' tree (tag: v5.2-rc1).

This is a patch set implementing movable objects within the SLUB
allocator.  This is work based on Christopher Lameter's patch set:

 https://lore.kernel.org/patchwork/project/lkml/list/?series=377335

The original code logic is from that set and implemented by Christopher.
Clean up, refactoring, documentation, and additional features by myself.
Responsibility for any bugs remaining falls solely with myself.

I am intending on sending a non-RFC version soon after this one (if
XArray stuff is ok).  If anyone has any objects with SMO in general
please yell at me now.

Changes to this version:

Patch XArray to use a separate slab cache.  Currently the radix tree and
XArray use the same slab cache.  Radix tree nodes can not be moved but
XArray nodes can.

Matthew,

Does this fit in ok with your plans for the XArray and radix tree?  I
don't really like the function names used here or the init function name
(xarray_slabcache_init()).  If there is a better way to do this please
mercilessly correct me :)


Thanks for looking at this,
Tobin.


Tobin C. Harding (16):
  slub: Add isolate() and migrate() methods
  tools/vm/slabinfo: Add support for -C and -M options
  slub: Sort slab cache list
  slub: Slab defrag core
  tools/vm/slabinfo: Add remote node defrag ratio output
  tools/vm/slabinfo: Add defrag_used_ratio output
  tools/testing/slab: Add object migration test module
  tools/testing/slab: Add object migration test suite
  lib: Separate radix_tree_node and xa_node slab cache
  xarray: Implement migration function for xa_node objects
  tools/testing/slab: Add XArray movable objects tests
  slub: Enable moving objects to/from specific nodes
  slub: Enable balancing slabs across nodes
  dcache: Provide a dentry constructor
  dcache: Implement partial shrink via Slab Movable Objects
  dcache: Add CONFIG_DCACHE_SMO

 Documentation/ABI/testing/sysfs-kernel-slab |  14 +
 fs/dcache.c                                 | 110 ++-
 include/linux/slab.h                        |  71 ++
 include/linux/slub_def.h                    |  10 +
 include/linux/xarray.h                      |   3 +
 init/main.c                                 |   2 +
 lib/radix-tree.c                            |   2 +-
 lib/xarray.c                                | 109 ++-
 mm/Kconfig                                  |  14 +
 mm/slab_common.c                            |   2 +-
 mm/slub.c                                   | 819 ++++++++++++++++++--
 tools/testing/slab/Makefile                 |  10 +
 tools/testing/slab/slub_defrag.c            | 567 ++++++++++++++
 tools/testing/slab/slub_defrag.py           | 451 +++++++++++
 tools/testing/slab/slub_defrag_xarray.c     | 211 +++++
 tools/vm/slabinfo.c                         |  51 +-
 16 files changed, 2343 insertions(+), 103 deletions(-)
 create mode 100644 tools/testing/slab/Makefile
 create mode 100644 tools/testing/slab/slub_defrag.c
 create mode 100755 tools/testing/slab/slub_defrag.py
 create mode 100644 tools/testing/slab/slub_defrag_xarray.c

-- 
2.21.0

[RFC PATCH v5 01/16] slub: Add isolate() and migrate() methods

[Tobin C. Harding]

Add the two methods needed for moving objects and enable the display of
the callbacks via the /sys/kernel/slab interface.

Add documentation explaining the use of these methods and the prototypes
for slab.h. Add functions to setup the callbacks method for a slab
cache.

Add empty functions for SLAB/SLOB. The API is generic so it could be
theoretically implemented for these allocators as well.

Change sysfs 'ctor' field to be 'ops' to contain all the callback
operations defined for a slab cache.  Display the existing 'ctor'
callback in the ops fields contents along with 'isolate' and 'migrate'
callbacks.

Co-developed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 include/linux/slab.h     | 70 ++++++++++++++++++++++++++++++++++++++++
 include/linux/slub_def.h |  3 ++
 mm/slub.c                | 59 +++++++++++++++++++++++++++++----
 3 files changed, 126 insertions(+), 6 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 9449b19c5f10..886fc130334d 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -154,6 +154,76 @@ void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
 void memcg_deactivate_kmem_caches(struct mem_cgroup *);
 void memcg_destroy_kmem_caches(struct mem_cgroup *);
 
+/*
+ * Function prototypes passed to kmem_cache_setup_mobility() to enable
+ * mobile objects and targeted reclaim in slab caches.
+ */
+
+/**
+ * typedef kmem_cache_isolate_func - Object migration callback function.
+ * @s: The cache we are working on.
+ * @ptr: Pointer to an array of pointers to the objects to isolate.
+ * @nr: Number of objects in @ptr array.
+ *
+ * The purpose of kmem_cache_isolate_func() is to pin each object so that
+ * they cannot be freed until kmem_cache_migrate_func() has processed
+ * them. This may be accomplished by increasing the refcount or setting
+ * a flag.
+ *
+ * The object pointer array passed is also passed to
+ * kmem_cache_migrate_func().  The function may remove objects from the
+ * array by setting pointers to %NULL. This is useful if we can
+ * determine that an object is being freed because
+ * kmem_cache_isolate_func() was called when the subsystem was calling
+ * kmem_cache_free().  In that case it is not necessary to increase the
+ * refcount or specially mark the object because the release of the slab
+ * lock will lead to the immediate freeing of the object.
+ *
+ * Context: Called with locks held so that the slab objects cannot be
+ *          freed.  We are in an atomic context and no slab operations
+ *          may be performed.
+ * Return: A pointer that is passed to the migrate function. If any
+ *         objects cannot be touched at this point then the pointer may
+ *         indicate a failure and then the migration function can simply
+ *         remove the references that were already obtained. The private
+ *         data could be used to track the objects that were already pinned.
+ */
+typedef void *kmem_cache_isolate_func(struct kmem_cache *s, void **ptr, int nr);
+
+/**
+ * typedef kmem_cache_migrate_func - Object migration callback function.
+ * @s: The cache we are working on.
+ * @ptr: Pointer to an array of pointers to the objects to migrate.
+ * @nr: Number of objects in @ptr array.
+ * @node: The NUMA node where the object should be allocated.
+ * @private: The pointer returned by kmem_cache_isolate_func().
+ *
+ * This function is responsible for migrating objects.  Typically, for
+ * each object in the input array you will want to allocate an new
+ * object, copy the original object, update any pointers, and free the
+ * old object.
+ *
+ * After this function returns all pointers to the old object should now
+ * point to the new object.
+ *
+ * Context: Called with no locks held and interrupts enabled.  Sleeping
+ *          is possible.  Any operation may be performed.
+ */
+typedef void kmem_cache_migrate_func(struct kmem_cache *s, void **ptr,
+				     int nr, int node, void *private);
+
+/*
+ * kmem_cache_setup_mobility() is used to setup callbacks for a slab cache.
+ */
+#ifdef CONFIG_SLUB
+void kmem_cache_setup_mobility(struct kmem_cache *, kmem_cache_isolate_func,
+			       kmem_cache_migrate_func);
+#else
+static inline void
+kmem_cache_setup_mobility(struct kmem_cache *s, kmem_cache_isolate_func isolate,
+			  kmem_cache_migrate_func migrate) {}
+#endif
+
 /*
  * Please use this macro to create slab caches. Simply specify the
  * name of the structure and maybe some flags that are listed above.
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index d2153789bd9f..2879a2f5f8eb 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -99,6 +99,9 @@ struct kmem_cache {
 	gfp_t allocflags;	/* gfp flags to use on each alloc */
 	int refcount;		/* Refcount for slab cache destroy */
 	void (*ctor)(void *);
+	kmem_cache_isolate_func *isolate;
+	kmem_cache_migrate_func *migrate;
+
 	unsigned int inuse;		/* Offset to metadata */
 	unsigned int align;		/* Alignment */
 	unsigned int red_left_pad;	/* Left redzone padding size */
diff --git a/mm/slub.c b/mm/slub.c
index cd04dbd2b5d0..1c380a2bc78a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4317,6 +4317,33 @@ int __kmem_cache_create(struct kmem_cache *s, slab_flags_t flags)
 	return err;
 }
 
+void kmem_cache_setup_mobility(struct kmem_cache *s,
+			       kmem_cache_isolate_func isolate,
+			       kmem_cache_migrate_func migrate)
+{
+	/*
+	 * Mobile objects must have a ctor otherwise the object may be
+	 * in an undefined state on allocation.  Since the object may
+	 * need to be inspected by the migration function at any time
+	 * after allocation we must ensure that the object always has a
+	 * defined state.
+	 */
+	if (!s->ctor) {
+		pr_err("%s: require constructor to setup mobility\n", s->name);
+		return;
+	}
+
+	s->isolate = isolate;
+	s->migrate = migrate;
+
+	/*
+	 * Sadly serialization requirements currently mean that we have
+	 * to disable fast cmpxchg based processing.
+	 */
+	s->flags &= ~__CMPXCHG_DOUBLE;
+}
+EXPORT_SYMBOL(kmem_cache_setup_mobility);
+
 void *__kmalloc_track_caller(size_t size, gfp_t gfpflags, unsigned long caller)
 {
 	struct kmem_cache *s;
@@ -5001,13 +5028,33 @@ static ssize_t cpu_partial_store(struct kmem_cache *s, const char *buf,
 }
 SLAB_ATTR(cpu_partial);
 
-static ssize_t ctor_show(struct kmem_cache *s, char *buf)
+static int op_show(char *buf, const char *txt, unsigned long addr)
 {
-	if (!s->ctor)
-		return 0;
-	return sprintf(buf, "%pS\n", s->ctor);
+	int x = 0;
+
+	x += sprintf(buf, "%s : ", txt);
+	x += sprint_symbol(buf + x, addr);
+	x += sprintf(buf + x, "\n");
+
+	return x;
+}
+
+static ssize_t ops_show(struct kmem_cache *s, char *buf)
+{
+	int x = 0;
+
+	if (s->ctor)
+		x += op_show(buf + x, "ctor", (unsigned long)s->ctor);
+
+	if (s->isolate)
+		x += op_show(buf + x, "isolate", (unsigned long)s->isolate);
+
+	if (s->migrate)
+		x += op_show(buf + x, "migrate", (unsigned long)s->migrate);
+
+	return x;
 }
-SLAB_ATTR_RO(ctor);
+SLAB_ATTR_RO(ops);
 
 static ssize_t aliases_show(struct kmem_cache *s, char *buf)
 {
@@ -5420,7 +5467,7 @@ static struct attribute *slab_attrs[] = {
 	&objects_partial_attr.attr,
 	&partial_attr.attr,
 	&cpu_slabs_attr.attr,
-	&ctor_attr.attr,
+	&ops_attr.attr,
 	&aliases_attr.attr,
 	&align_attr.attr,
 	&hwcache_align_attr.attr,
-- 
2.21.0

[RFC PATCH v5 02/16] tools/vm/slabinfo: Add support for -C and -M options

[Tobin C. Harding]

-C lists caches that use a ctor.

-M lists caches that support object migration.

Add command line options to show caches with a constructor and caches
that are movable (i.e. have migrate function).

Co-developed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 tools/vm/slabinfo.c | 40 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 4 deletions(-)

diff --git a/tools/vm/slabinfo.c b/tools/vm/slabinfo.c
index 73818f1b2ef8..cbfc56c44c2f 100644
--- a/tools/vm/slabinfo.c
+++ b/tools/vm/slabinfo.c
@@ -33,6 +33,7 @@ struct slabinfo {
 	unsigned int hwcache_align, object_size, objs_per_slab;
 	unsigned int sanity_checks, slab_size, store_user, trace;
 	int order, poison, reclaim_account, red_zone;
+	int movable, ctor;
 	unsigned long partial, objects, slabs, objects_partial, objects_total;
 	unsigned long alloc_fastpath, alloc_slowpath;
 	unsigned long free_fastpath, free_slowpath;
@@ -67,6 +68,8 @@ int show_report;
 int show_alias;
 int show_slab;
 int skip_zero = 1;
+int show_movable;
+int show_ctor;
 int show_numa;
 int show_track;
 int show_first_alias;
@@ -109,11 +112,13 @@ static void fatal(const char *x, ...)
 
 static void usage(void)
 {
-	printf("slabinfo 4/15/2011. (c) 2007 sgi/(c) 2011 Linux Foundation.\n\n"
-		"slabinfo [-aADefhilnosrStTvz1LXBU] [N=K] [-dafzput] [slab-regexp]\n"
+	printf("slabinfo 4/15/2017. (c) 2007 sgi/(c) 2011 Linux Foundation/(c) 2017 Jump Trading LLC.\n\n"
+	       "slabinfo [-aACDefhilMnosrStTvz1LXBU] [N=K] [-dafzput] [slab-regexp]\n"
+
 		"-a|--aliases           Show aliases\n"
 		"-A|--activity          Most active slabs first\n"
 		"-B|--Bytes             Show size in bytes\n"
+		"-C|--ctor              Show slabs with ctors\n"
 		"-D|--display-active    Switch line format to activity\n"
 		"-e|--empty             Show empty slabs\n"
 		"-f|--first-alias       Show first alias\n"
@@ -121,6 +126,7 @@ static void usage(void)
 		"-i|--inverted          Inverted list\n"
 		"-l|--slabs             Show slabs\n"
 		"-L|--Loss              Sort by loss\n"
+		"-M|--movable           Show caches that support movable objects\n"
 		"-n|--numa              Show NUMA information\n"
 		"-N|--lines=K           Show the first K slabs\n"
 		"-o|--ops               Show kmem_cache_ops\n"
@@ -588,6 +594,12 @@ static void slabcache(struct slabinfo *s)
 	if (show_empty && s->slabs)
 		return;
 
+	if (show_ctor && !s->ctor)
+		return;
+
+	if (show_movable && !s->movable)
+		return;
+
 	if (sort_loss == 0)
 		store_size(size_str, slab_size(s));
 	else
@@ -602,6 +614,10 @@ static void slabcache(struct slabinfo *s)
 		*p++ = '*';
 	if (s->cache_dma)
 		*p++ = 'd';
+	if (s->ctor)
+		*p++ = 'C';
+	if (s->movable)
+		*p++ = 'M';
 	if (s->hwcache_align)
 		*p++ = 'A';
 	if (s->poison)
@@ -636,7 +652,8 @@ static void slabcache(struct slabinfo *s)
 		printf("%-21s %8ld %7d %15s %14s %4d %1d %3ld %3ld %s\n",
 			s->name, s->objects, s->object_size, size_str, dist_str,
 			s->objs_per_slab, s->order,
-			s->slabs ? (s->partial * 100) / s->slabs : 100,
+			s->slabs ? (s->partial * 100) /
+					(s->slabs * s->objs_per_slab) : 100,
 			s->slabs ? (s->objects * s->object_size * 100) /
 				(s->slabs * (page_size << s->order)) : 100,
 			flags);
@@ -1256,6 +1273,13 @@ static void read_slab_dir(void)
 			slab->alloc_node_mismatch = get_obj("alloc_node_mismatch");
 			slab->deactivate_bypass = get_obj("deactivate_bypass");
 			chdir("..");
+			if (read_slab_obj(slab, "ops")) {
+				if (strstr(buffer, "ctor :"))
+					slab->ctor = 1;
+				if (strstr(buffer, "migrate :"))
+					slab->movable = 1;
+			}
+
 			if (slab->name[0] == ':')
 				alias_targets++;
 			slab++;
@@ -1332,6 +1356,8 @@ static void xtotals(void)
 }
 
 struct option opts[] = {
+	{ "ctor", no_argument, NULL, 'C' },
+	{ "movable", no_argument, NULL, 'M' },
 	{ "aliases", no_argument, NULL, 'a' },
 	{ "activity", no_argument, NULL, 'A' },
 	{ "debug", optional_argument, NULL, 'd' },
@@ -1367,7 +1393,7 @@ int main(int argc, char *argv[])
 
 	page_size = getpagesize();
 
-	while ((c = getopt_long(argc, argv, "aAd::Defhil1noprstvzTSN:LXBU",
+	while ((c = getopt_long(argc, argv, "aACd::Defhil1MnoprstvzTSN:LXBU",
 						opts, NULL)) != -1)
 		switch (c) {
 		case '1':
@@ -1376,6 +1402,9 @@ int main(int argc, char *argv[])
 		case 'a':
 			show_alias = 1;
 			break;
+		case 'C':
+			show_ctor = 1;
+			break;
 		case 'A':
 			sort_active = 1;
 			break;
@@ -1399,6 +1428,9 @@ int main(int argc, char *argv[])
 		case 'i':
 			show_inverted = 1;
 			break;
+		case 'M':
+			show_movable = 1;
+			break;
 		case 'n':
 			show_numa = 1;
 			break;
-- 
2.21.0

[RFC PATCH v5 03/16] slub: Sort slab cache list

[Tobin C. Harding]

It is advantageous to have all defragmentable slabs together at the
beginning of the list of slabs so that there is no need to scan the
complete list. Put defragmentable caches first when adding a slab cache
and others last.

Co-developed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 mm/slab_common.c | 2 +-
 mm/slub.c        | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 58251ba63e4a..db5e9a0b1535 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -393,7 +393,7 @@ static struct kmem_cache *create_cache(const char *name,
 		goto out_free_cache;
 
 	s->refcount = 1;
-	list_add(&s->list, &slab_caches);
+	list_add_tail(&s->list, &slab_caches);
 	memcg_link_cache(s);
 out:
 	if (err)
diff --git a/mm/slub.c b/mm/slub.c
index 1c380a2bc78a..66d474397c0f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4333,6 +4333,8 @@ void kmem_cache_setup_mobility(struct kmem_cache *s,
 		return;
 	}
 
+	mutex_lock(&slab_mutex);
+
 	s->isolate = isolate;
 	s->migrate = migrate;
 
@@ -4341,6 +4343,10 @@ void kmem_cache_setup_mobility(struct kmem_cache *s,
 	 * to disable fast cmpxchg based processing.
 	 */
 	s->flags &= ~__CMPXCHG_DOUBLE;
+
+	list_move(&s->list, &slab_caches);	/* Move to top */
+
+	mutex_unlock(&slab_mutex);
 }
 EXPORT_SYMBOL(kmem_cache_setup_mobility);
 
-- 
2.21.0

[RFC PATCH v5 04/16] slub: Slab defrag core

[Tobin C. Harding]

Internal fragmentation can occur within pages used by the slub
allocator.  Under some workloads large numbers of pages can be used by
partial slab pages.  This under-utilisation is bad simply because it
wastes memory but also because if the system is under memory pressure
higher order allocations may become difficult to satisfy.  If we can
defrag slab caches we can alleviate these problems.

Implement Slab Movable Objects in order to defragment slab caches.

Slab defragmentation may occur:

1. Unconditionally when __kmem_cache_shrink() is called on a slab cache
   by the kernel calling kmem_cache_shrink().

2. Unconditionally through the use of the slabinfo command.

	slabinfo <cache> -s

3. Conditionally via the use of kmem_cache_defrag()

- Use Slab Movable Objects when shrinking cache.

Currently when the kernel calls kmem_cache_shrink() we curate the
partial slabs list.  If object migration is not enabled for the cache we
still do this, if however, SMO is enabled we attempt to move objects in
partially full slabs in order to defragment the cache.  Shrink attempts
to move all objects in order to reduce the cache to a single partial
slab for each node.

- Add conditional per node defrag via new function:

	kmem_defrag_slabs(int node).

kmem_defrag_slabs() attempts to defragment all slab caches for
node. Defragmentation is done conditionally dependent on MAX_PARTIAL
_and_ defrag_used_ratio.

   Caches are only considered for defragmentation if the number of
   partial slabs exceeds MAX_PARTIAL (per node).

   Also, defragmentation only occurs if the usage ratio of the slab is
   lower than the configured percentage (sysfs field added in this
   patch).  Fragmentation ratios are measured by calculating the
   percentage of objects in use compared to the total number of objects
   that the slab page can accommodate.

   The scanning of slab caches is optimized because the defragmentable
   slabs come first on the list. Thus we can terminate scans on the
   first slab encountered that does not support defragmentation.

   kmem_defrag_slabs() takes a node parameter. This can either be -1 if
   defragmentation should be performed on all nodes, or a node number.

   Defragmentation may be disabled by setting defrag ratio to 0

	echo 0 > /sys/kernel/slab/<cache>/defrag_used_ratio

- Add a defrag ratio sysfs field and set it to 30% by default. A limit
of 30% specifies that more than 3 out of 10 available slots for objects
need to be in use otherwise slab defragmentation will be attempted on
the remaining objects.

In order for a cache to be defragmentable the cache must support object
migration (SMO).  Enabling SMO for a cache is done via a call to the
recently added function:

	void kmem_cache_setup_mobility(struct kmem_cache *,
				       kmem_cache_isolate_func,
			               kmem_cache_migrate_func);

Co-developed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 Documentation/ABI/testing/sysfs-kernel-slab |  14 +
 include/linux/slab.h                        |   1 +
 include/linux/slub_def.h                    |   7 +
 mm/slub.c                                   | 385 ++++++++++++++++----
 4 files changed, 334 insertions(+), 73 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-slab b/Documentation/ABI/testing/sysfs-kernel-slab
index 29601d93a1c2..c6f129af035a 100644
--- a/Documentation/ABI/testing/sysfs-kernel-slab
+++ b/Documentation/ABI/testing/sysfs-kernel-slab
@@ -180,6 +180,20 @@ Description:
 		list.  It can be written to clear the current count.
 		Available when CONFIG_SLUB_STATS is enabled.
 
+What:		/sys/kernel/slab/cache/defrag_used_ratio
+Date:		May 2019
+KernelVersion:	5.2
+Contact:	Christoph Lameter <cl@linux-foundation.org>
+		Pekka Enberg <penberg@cs.helsinki.fi>,
+Description:
+		The defrag_used_ratio file allows the control of how aggressive
+		slab fragmentation reduction works at reclaiming objects from
+		sparsely populated slabs. This is a percentage. If a slab has
+		less than this percentage of objects allocated then reclaim will
+		attempt to reclaim objects so that the whole slab page can be
+		freed. 0% specifies no reclaim attempt (defrag disabled), 100%
+		specifies attempt to reclaim all pages.  The default is 30%.
+
 What:		/sys/kernel/slab/cache/deactivate_to_tail
 Date:		February 2008
 KernelVersion:	2.6.25
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 886fc130334d..4bf381b34829 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -149,6 +149,7 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name,
 			void (*ctor)(void *));
 void kmem_cache_destroy(struct kmem_cache *);
 int kmem_cache_shrink(struct kmem_cache *);
+unsigned long kmem_defrag_slabs(int node);
 
 void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
 void memcg_deactivate_kmem_caches(struct mem_cgroup *);
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 2879a2f5f8eb..34c6f1250652 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -107,6 +107,13 @@ struct kmem_cache {
 	unsigned int red_left_pad;	/* Left redzone padding size */
 	const char *name;	/* Name (only for display!) */
 	struct list_head list;	/* List of slab caches */
+	int defrag_used_ratio;	/*
+				 * Ratio used to check against the
+				 * percentage of objects allocated in a
+				 * slab page.  If less than this ratio
+				 * is allocated then reclaim attempts
+				 * are made.
+				 */
 #ifdef CONFIG_SYSFS
 	struct kobject kobj;	/* For sysfs */
 	struct work_struct kobj_remove_work;
diff --git a/mm/slub.c b/mm/slub.c
index 66d474397c0f..2157205df7ba 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -355,6 +355,12 @@ static __always_inline void slab_lock(struct page *page)
 	bit_spin_lock(PG_locked, &page->flags);
 }
 
+static __always_inline int slab_trylock(struct page *page)
+{
+	VM_BUG_ON_PAGE(PageTail(page), page);
+	return bit_spin_trylock(PG_locked, &page->flags);
+}
+
 static __always_inline void slab_unlock(struct page *page)
 {
 	VM_BUG_ON_PAGE(PageTail(page), page);
@@ -3634,6 +3640,7 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 
 	set_cpu_partial(s);
 
+	s->defrag_used_ratio = 30;
 #ifdef CONFIG_NUMA
 	s->remote_node_defrag_ratio = 1000;
 #endif
@@ -3950,79 +3957,6 @@ void kfree(const void *x)
 }
 EXPORT_SYMBOL(kfree);
 
-#define SHRINK_PROMOTE_MAX 32
-
-/*
- * kmem_cache_shrink discards empty slabs and promotes the slabs filled
- * up most to the head of the partial lists. New allocations will then
- * fill those up and thus they can be removed from the partial lists.
- *
- * The slabs with the least items are placed last. This results in them
- * being allocated from last increasing the chance that the last objects
- * are freed in them.
- */
-int __kmem_cache_shrink(struct kmem_cache *s)
-{
-	int node;
-	int i;
-	struct kmem_cache_node *n;
-	struct page *page;
-	struct page *t;
-	struct list_head discard;
-	struct list_head promote[SHRINK_PROMOTE_MAX];
-	unsigned long flags;
-	int ret = 0;
-
-	flush_all(s);
-	for_each_kmem_cache_node(s, node, n) {
-		INIT_LIST_HEAD(&discard);
-		for (i = 0; i < SHRINK_PROMOTE_MAX; i++)
-			INIT_LIST_HEAD(promote + i);
-
-		spin_lock_irqsave(&n->list_lock, flags);
-
-		/*
-		 * Build lists of slabs to discard or promote.
-		 *
-		 * Note that concurrent frees may occur while we hold the
-		 * list_lock. page->inuse here is the upper limit.
-		 */
-		list_for_each_entry_safe(page, t, &n->partial, slab_list) {
-			int free = page->objects - page->inuse;
-
-			/* Do not reread page->inuse */
-			barrier();
-
-			/* We do not keep full slabs on the list */
-			BUG_ON(free <= 0);
-
-			if (free == page->objects) {
-				list_move(&page->slab_list, &discard);
-				n->nr_partial--;
-			} else if (free <= SHRINK_PROMOTE_MAX)
-				list_move(&page->slab_list, promote + free - 1);
-		}
-
-		/*
-		 * Promote the slabs filled up most to the head of the
-		 * partial list.
-		 */
-		for (i = SHRINK_PROMOTE_MAX - 1; i >= 0; i--)
-			list_splice(promote + i, &n->partial);
-
-		spin_unlock_irqrestore(&n->list_lock, flags);
-
-		/* Release empty slabs */
-		list_for_each_entry_safe(page, t, &discard, slab_list)
-			discard_slab(s, page);
-
-		if (slabs_node(s, node))
-			ret = 1;
-	}
-
-	return ret;
-}
-
 #ifdef CONFIG_MEMCG
 static void kmemcg_cache_deact_after_rcu(struct kmem_cache *s)
 {
@@ -4317,6 +4251,287 @@ int __kmem_cache_create(struct kmem_cache *s, slab_flags_t flags)
 	return err;
 }
 
+/*
+ * Allocate a slab scratch space that is sufficient to keep pointers to
+ * individual objects for all objects in cache and also a bitmap for the
+ * objects (used to mark which objects are active).
+ */
+static inline void *alloc_scratch(struct kmem_cache *s)
+{
+	unsigned int size = oo_objects(s->max);
+
+	return kmalloc(size * sizeof(void *) +
+		       BITS_TO_LONGS(size) * sizeof(unsigned long),
+		       GFP_KERNEL);
+}
+
+/*
+ * move_slab_page() - Move all objects in the given slab.
+ * @page: The slab we are working on.
+ * @scratch: Pointer to scratch space.
+ * @node: The target node to move objects to.
+ *
+ * If the target node is not the current node then the object is moved
+ * to the target node.  If the target node is the current node then this
+ * is an effective way of defragmentation since the current slab page
+ * with its object is exempt from allocation.
+ */
+static void move_slab_page(struct page *page, void *scratch, int node)
+{
+	unsigned long objects;
+	struct kmem_cache *s;
+	unsigned long flags;
+	unsigned long *map;
+	void *private;
+	int count;
+	void *p;
+	void **vector = scratch;
+	void *addr = page_address(page);
+
+	local_irq_save(flags);
+	slab_lock(page);
+
+	BUG_ON(!PageSlab(page)); /* Must be a slab page */
+	BUG_ON(!page->frozen);	 /* Slab must have been frozen earlier */
+
+	s = page->slab_cache;
+	objects = page->objects;
+	map = scratch + objects * sizeof(void **);
+
+	/* Determine used objects */
+	bitmap_fill(map, objects);
+	for (p = page->freelist; p; p = get_freepointer(s, p))
+		__clear_bit(slab_index(p, s, addr), map);
+
+	/* Build vector of pointers to objects */
+	count = 0;
+	memset(vector, 0, objects * sizeof(void **));
+	for_each_object(p, s, addr, objects)
+		if (test_bit(slab_index(p, s, addr), map))
+			vector[count++] = p;
+
+	if (s->isolate)
+		private = s->isolate(s, vector, count);
+	else
+		/* Objects do not need to be isolated */
+		private = NULL;
+
+	/*
+	 * Pinned the objects. Now we can drop the slab lock. The slab
+	 * is frozen so it cannot vanish from under us nor will
+	 * allocations be performed on the slab. However, unlocking the
+	 * slab will allow concurrent slab_frees to proceed. So the
+	 * subsystem must have a way to tell from the content of the
+	 * object that it was freed.
+	 *
+	 * If neither RCU nor ctor is being used then the object may be
+	 * modified by the allocator after being freed which may disrupt
+	 * the ability of the migrate function to tell if the object is
+	 * free or not.
+	 */
+	slab_unlock(page);
+	local_irq_restore(flags);
+
+	/* Perform callback to move the objects */
+	s->migrate(s, vector, count, node, private);
+}
+
+/*
+ * kmem_cache_defrag() - Defragment node.
+ * @s: cache we are working on.
+ * @node: The node to move objects from.
+ * @target_node: The node to move objects to.
+ * @ratio: The defrag ratio (percentage, between 0 and 100).
+ *
+ * Release slabs with zero objects and try to call the migration function
+ * for slabs with less than the 'ratio' percentage of objects allocated.
+ *
+ * Moved objects are allocated on @target_node.
+ *
+ * Return: The number of partial slabs left on @node after the
+ *         operation.
+ */
+static unsigned long kmem_cache_defrag(struct kmem_cache *s,
+				       int node, int target_node, int ratio)
+{
+	struct kmem_cache_node *n = get_node(s, node);
+	struct page *page, *page2;
+	LIST_HEAD(move_list);
+	unsigned long flags;
+
+	if (node == target_node && n->nr_partial <= 1) {
+		/*
+		 * Trying to reduce fragmentation on a node but there is
+		 * only a single or no partial slab page. This is already
+		 * the optimal object density that we can reach.
+		 */
+		return n->nr_partial;
+	}
+
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry_safe(page, page2, &n->partial, lru) {
+		if (!slab_trylock(page))
+			/* Busy slab. Get out of the way */
+			continue;
+
+		if (page->inuse) {
+			if (page->inuse > ratio * page->objects / 100) {
+				slab_unlock(page);
+				/*
+				 * Skip slab because the object density
+				 * in the slab page is high enough.
+				 */
+				continue;
+			}
+
+			list_move(&page->lru, &move_list);
+			if (s->migrate) {
+				/* Stop page being considered for allocations */
+				n->nr_partial--;
+				page->frozen = 1;
+			}
+			slab_unlock(page);
+		} else {	/* Empty slab page */
+			list_del(&page->lru);
+			n->nr_partial--;
+			slab_unlock(page);
+			discard_slab(s, page);
+		}
+	}
+
+	if (!s->migrate) {
+		/*
+		 * No defrag method. By simply putting the zaplist at
+		 * the end of the partial list we can let them simmer
+		 * longer and thus increase the chance of all objects
+		 * being reclaimed.
+		 */
+		list_splice(&move_list, n->partial.prev);
+	}
+
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	if (s->migrate && !list_empty(&move_list)) {
+		void **scratch = alloc_scratch(s);
+		if (scratch) {
+			/* Try to remove / move the objects left */
+			list_for_each_entry(page, &move_list, lru) {
+				if (page->inuse)
+					move_slab_page(page, scratch, target_node);
+			}
+			kfree(scratch);
+		}
+
+		/* Inspect results and dispose of pages */
+		spin_lock_irqsave(&n->list_lock, flags);
+		list_for_each_entry_safe(page, page2, &move_list, lru) {
+			list_del(&page->lru);
+			slab_lock(page);
+			page->frozen = 0;
+
+			if (page->inuse) {
+				/*
+				 * Objects left in slab page, move it to the
+				 * tail of the partial list to increase the
+				 * chance that the freeing of the remaining
+				 * objects will free the slab page.
+				 */
+				n->nr_partial++;
+				list_add_tail(&page->lru, &n->partial);
+				slab_unlock(page);
+			} else {
+				slab_unlock(page);
+				discard_slab(s, page);
+			}
+		}
+		spin_unlock_irqrestore(&n->list_lock, flags);
+	}
+
+	return n->nr_partial;
+}
+
+/**
+ * kmem_defrag_slabs() - Defrag slab caches.
+ * @node: The node to defrag or -1 for all nodes.
+ *
+ * Defrag slabs conditional on the amount of fragmentation in a page.
+ *
+ * Return: The total number of partial slabs in migratable caches left
+ *         on @node after the operation.
+ */
+unsigned long kmem_defrag_slabs(int node)
+{
+	struct kmem_cache *s;
+	unsigned long left = 0;
+	int nid;
+
+	if (node >= MAX_NUMNODES)
+		return -EINVAL;
+
+	/*
+	 * kmem_defrag_slabs() may be called from the reclaim path which
+	 * may be called for any page allocator alloc. So there is the
+	 * danger that we get called in a situation where slub already
+	 * acquired the slub_lock for other purposes.
+	 */
+	if (!mutex_trylock(&slab_mutex))
+		return 0;
+
+	list_for_each_entry(s, &slab_caches, list) {
+		/*
+		 * Defragmentable caches come first. If the slab cache is
+		 * not defragmentable then we can stop traversing the list.
+		 */
+		if (!s->migrate)
+			break;
+
+		if (node >= 0) {
+			if (s->node[node]->nr_partial > MAX_PARTIAL) {
+				left += kmem_cache_defrag(s, node, node,
+							  s->defrag_used_ratio);
+			}
+			continue;
+		}
+
+		for_each_node_state(nid, N_NORMAL_MEMORY) {
+			if (s->node[nid]->nr_partial > MAX_PARTIAL) {
+				left += kmem_cache_defrag(s, nid, nid,
+							  s->defrag_used_ratio);
+			}
+		}
+	}
+	mutex_unlock(&slab_mutex);
+	return left;
+}
+EXPORT_SYMBOL(kmem_defrag_slabs);
+
+/**
+ * __kmem_cache_shrink() - Shrink a cache.
+ * @s: The cache to shrink.
+ *
+ * Reduces the memory footprint of a slab cache by as much as possible.
+ *
+ * This works by:
+ *  1. Removing empty slabs from the partial list.
+ *  2. Migrating slab objects to denser slab pages if the slab cache
+ *  supports migration.  If not, reorganizing the partial list so that
+ *  more densely allocated slab pages come first.
+ *
+ * Not called directly, called by kmem_cache_shrink().
+ */
+int __kmem_cache_shrink(struct kmem_cache *s)
+{
+	int node;
+	int left = 0;
+
+	flush_all(s);
+	for_each_node_state(node, N_NORMAL_MEMORY)
+		left += kmem_cache_defrag(s, node, node, 100);
+
+	return left;
+}
+EXPORT_SYMBOL(__kmem_cache_shrink);
+
 void kmem_cache_setup_mobility(struct kmem_cache *s,
 			       kmem_cache_isolate_func isolate,
 			       kmem_cache_migrate_func migrate)
@@ -5168,6 +5383,29 @@ static ssize_t destroy_by_rcu_show(struct kmem_cache *s, char *buf)
 }
 SLAB_ATTR_RO(destroy_by_rcu);
 
+static ssize_t defrag_used_ratio_show(struct kmem_cache *s, char *buf)
+{
+	return sprintf(buf, "%d\n", s->defrag_used_ratio);
+}
+
+static ssize_t defrag_used_ratio_store(struct kmem_cache *s,
+				       const char *buf, size_t length)
+{
+	unsigned long ratio;
+	int err;
+
+	err = kstrtoul(buf, 10, &ratio);
+	if (err)
+		return err;
+
+	if (ratio > 100)
+		return -EINVAL;
+
+	s->defrag_used_ratio = ratio;
+	return length;
+}
+SLAB_ATTR(defrag_used_ratio);
+
 #ifdef CONFIG_SLUB_DEBUG
 static ssize_t slabs_show(struct kmem_cache *s, char *buf)
 {
@@ -5492,6 +5730,7 @@ static struct attribute *slab_attrs[] = {
 	&validate_attr.attr,
 	&alloc_calls_attr.attr,
 	&free_calls_attr.attr,
+	&defrag_used_ratio_attr.attr,
 #endif
 #ifdef CONFIG_ZONE_DMA
 	&cache_dma_attr.attr,
-- 
2.21.0

[RFC PATCH v5 05/16] tools/vm/slabinfo: Add remote node defrag ratio output

[Tobin C. Harding]

Add output line for NUMA remote node defrag ratio.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 tools/vm/slabinfo.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/vm/slabinfo.c b/tools/vm/slabinfo.c
index cbfc56c44c2f..d2c22f9ee2d8 100644
--- a/tools/vm/slabinfo.c
+++ b/tools/vm/slabinfo.c
@@ -34,6 +34,7 @@ struct slabinfo {
 	unsigned int sanity_checks, slab_size, store_user, trace;
 	int order, poison, reclaim_account, red_zone;
 	int movable, ctor;
+	int remote_node_defrag_ratio;
 	unsigned long partial, objects, slabs, objects_partial, objects_total;
 	unsigned long alloc_fastpath, alloc_slowpath;
 	unsigned long free_fastpath, free_slowpath;
@@ -377,6 +378,10 @@ static void slab_numa(struct slabinfo *s, int mode)
 	if (skip_zero && !s->slabs)
 		return;
 
+	if (mode) {
+		printf("\nNUMA remote node defrag ratio: %3d\n",
+		       s->remote_node_defrag_ratio);
+	}
 	if (!line) {
 		printf("\n%-21s:", mode ? "NUMA nodes" : "Slab");
 		for(node = 0; node <= highest_node; node++)
@@ -1272,6 +1277,8 @@ static void read_slab_dir(void)
 			slab->cpu_partial_free = get_obj("cpu_partial_free");
 			slab->alloc_node_mismatch = get_obj("alloc_node_mismatch");
 			slab->deactivate_bypass = get_obj("deactivate_bypass");
+			slab->remote_node_defrag_ratio =
+					get_obj("remote_node_defrag_ratio");
 			chdir("..");
 			if (read_slab_obj(slab, "ops")) {
 				if (strstr(buffer, "ctor :"))
-- 
2.21.0

[RFC PATCH v5 06/16] tools/vm/slabinfo: Add defrag_used_ratio output

[Tobin C. Harding]

Add output for the newly added defrag_used_ratio sysfs knob.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 tools/vm/slabinfo.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/vm/slabinfo.c b/tools/vm/slabinfo.c
index d2c22f9ee2d8..ef4ff93df4cc 100644
--- a/tools/vm/slabinfo.c
+++ b/tools/vm/slabinfo.c
@@ -34,6 +34,7 @@ struct slabinfo {
 	unsigned int sanity_checks, slab_size, store_user, trace;
 	int order, poison, reclaim_account, red_zone;
 	int movable, ctor;
+	int defrag_used_ratio;
 	int remote_node_defrag_ratio;
 	unsigned long partial, objects, slabs, objects_partial, objects_total;
 	unsigned long alloc_fastpath, alloc_slowpath;
@@ -549,6 +550,8 @@ static void report(struct slabinfo *s)
 		printf("** Slabs are destroyed via RCU\n");
 	if (s->reclaim_account)
 		printf("** Reclaim accounting active\n");
+	if (s->movable)
+		printf("** Defragmentation at %d%%\n", s->defrag_used_ratio);
 
 	printf("\nSizes (bytes)     Slabs              Debug                Memory\n");
 	printf("------------------------------------------------------------------------\n");
@@ -1279,6 +1282,7 @@ static void read_slab_dir(void)
 			slab->deactivate_bypass = get_obj("deactivate_bypass");
 			slab->remote_node_defrag_ratio =
 					get_obj("remote_node_defrag_ratio");
+			slab->defrag_used_ratio = get_obj("defrag_used_ratio");
 			chdir("..");
 			if (read_slab_obj(slab, "ops")) {
 				if (strstr(buffer, "ctor :"))
-- 
2.21.0

[RFC PATCH v5 07/16] tools/testing/slab: Add object migration test module

[Tobin C. Harding]

We just implemented slab movable objects for the SLUB allocator.  We
should test that code.  In order to do so we need to be able to do a
number of things

 - Create a cache
 - Enable Slab Movable Objects for the cache
 - Allocate objects to the cache
 - Free objects from within specific slabs of the cache

We can do all this via a loadable module.

Add a module that defines functions that can be triggered from userspace
via a debugfs entry. From the source:

  /*
   * SLUB defragmentation a.k.a. Slab Movable Objects (SMO).
   *
   * This module is used for testing the SLUB allocator.  Enables
   * userspace to run kernel functions via a debugfs file.
   *
   *   debugfs: /sys/kernel/debugfs/smo/callfn (write only)
   *
   * String written to `callfn` is parsed by the module and associated
   * function is called.  See fn_tab for mapping of strings to functions.
   */

References to allocated objects are kept by the module in a linked list
so that userspace can control which object to free.

We introduce the following four functions via the function table

  "enable": Enables object migration for the test cache.
  "alloc X": Allocates X objects
  "free X [Y]": Frees X objects starting at list position Y (default Y==0)
  "test": Runs [stress] tests from within the module (see below).

       {"enable", smo_enable_cache_mobility},
       {"alloc", smo_alloc_objects},
       {"free", smo_free_object},
       {"test", smo_run_module_tests},

Freeing from the start of the list creates a hole in the slab being
freed from (i.e. creates a partial slab).  The results of running these
commands can be see using `slabinfo` (available in tools/vm/):

	make -o slabinfo tools/vm/slabinfo.c

Stress tests can be run from within the module.  These tests are
internal to the module because we verify that object references are
still good after object migration.  These are called 'stress' tests
because it is intended that they create/free a lot of objects.
Userspace can control the number of objects to create, default is 1000.

Example test session
--------------------

Relevant /proc/slabinfo column headers:

  name   <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab>

  # mount -t debugfs none /sys/kernel/debug/
  $ cd path/to/linux/tools/testing/slab; make
  ...

  # insmod slub_defrag.ko
  # cat /proc/slabinfo | grep smo_test | sed 's/:.*//'
  smo_test               0      0    392   20    2

From this we can see that the module created cache 'smo_test' with 20
objects per slab and 2 pages per slab (and cache is currently empty).

We can play with the slab allocator manually:

  # insmod slub_defrag.ko
  # echo 'alloc 21' > callfn
  # cat /proc/slabinfo | grep smo_test | sed 's/:.*//'
  smo_test              21     40    392   20    2

We see here that 21 active objects have been allocated creating 2
slabs (40 total objects).

  # slabinfo smo_test --report

  Slabcache: smo_test         Aliases:  0 Order :  1 Objects: 21

  Sizes (bytes)     Slabs              Debug                Memory
  ------------------------------------------------------------------------
  Object :      56  Total  :       2   Sanity Checks : On   Total:   16384
  SlabObj:     392  Full   :       1   Redzoning     : On   Used :    1176
  SlabSiz:    8192  Partial:       1   Poisoning     : On   Loss :   15208
  Loss   :     336  CpuSlab:       0   Tracking      : On   Lalig:    7056
  Align  :       8  Objects:      20   Tracing       : Off  Lpadd:     704

Now free an object from the first slot of the first slab

  # echo 'free 1' > callfn
  # cat /proc/slabinfo | grep smo_test | sed 's/:.*//'
  smo_test              20     40    392   20    2

  # slabinfo smo_test --report

  Slabcache: smo_test         Aliases:  0 Order :  1 Objects: 20

  Sizes (bytes)     Slabs              Debug                Memory
  ------------------------------------------------------------------------
  Object :      56  Total  :       2   Sanity Checks : On   Total:   16384
  SlabObj:     392  Full   :       0   Redzoning     : On   Used :    1120
  SlabSiz:    8192  Partial:       2   Poisoning     : On   Loss :   15264
  Loss   :     336  CpuSlab:       0   Tracking      : On   Lalig:    6720
  Align  :       8  Objects:      20   Tracing       : Off  Lpadd:     704

Calling shrink now on the cache does nothing because object migration is
not enabled (output omitted).  If we enable object migration then shrink
the cache we expect the object from the second slab to me moved to the
first slot in the first slab and the second slab to be removed from the
partial list.

  # echo 'enable' > callfn
  # slabinfo smo_test --shrink
  # slabinfo smo_test --report

  Slabcache: smo_test         Aliases:  0 Order :  1 Objects: 20
  ** Defragmentation at 30%

  Sizes (bytes)     Slabs              Debug                Memory
  ------------------------------------------------------------------------
  Object :      56  Total  :       1   Sanity Checks : On   Total:    8192
  SlabObj:     392  Full   :       1   Redzoning     : On   Used :    1120
  SlabSiz:    8192  Partial:       0   Poisoning     : On   Loss :    7072
  Loss   :     336  CpuSlab:       0   Tracking      : On   Lalig:    6720
  Align  :       8  Objects:      20   Tracing       : Off  Lpadd:     352

We can run the stress tests (with the default number of objects):

  # cd /sys/kernel/debug/smo
  # echo 'test' > callfn
  [    3.576617] smo: test using nr_objs: 1000 keep: 10
  [    3.580169] smo: Module tests completed successfully

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 tools/testing/slab/Makefile      |  10 +
 tools/testing/slab/slub_defrag.c | 566 +++++++++++++++++++++++++++++++
 2 files changed, 576 insertions(+)
 create mode 100644 tools/testing/slab/Makefile
 create mode 100644 tools/testing/slab/slub_defrag.c

diff --git a/tools/testing/slab/Makefile b/tools/testing/slab/Makefile
new file mode 100644
index 000000000000..440c2e3e356f
--- /dev/null
+++ b/tools/testing/slab/Makefile
@@ -0,0 +1,10 @@
+obj-m += slub_defrag.o
+
+KTREE=../../..
+
+all:
+	make -C ${KTREE} M=$(PWD) modules
+
+clean:
+	make -C ${KTREE} M=$(PWD) clean
+
diff --git a/tools/testing/slab/slub_defrag.c b/tools/testing/slab/slub_defrag.c
new file mode 100644
index 000000000000..4a5c24394b96
--- /dev/null
+++ b/tools/testing/slab/slub_defrag.c
@@ -0,0 +1,566 @@
+// SPDX-License-Identifier: GPL-2.0+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+#include <linux/list.h>
+#include <linux/gfp.h>
+#include <linux/debugfs.h>
+#include <linux/numa.h>
+
+/*
+ * SLUB defragmentation a.k.a. Slab Movable Objects (SMO).
+ *
+ * This module is used for testing the SLUB allocator.  Enables
+ * userspace to run kernel functions via a debugfs file.
+ *
+ *   debugfs: /sys/kernel/debugfs/smo/callfn (write only)
+ *
+ * String written to `callfn` is parsed by the module and associated
+ * function is called.  See fn_tab for mapping of strings to functions.
+ */
+
+/* debugfs commands accept two optional arguments */
+#define SMO_CMD_DEFAUT_ARG -1
+
+#define SMO_DEBUGFS_DIR "smo"
+struct dentry *smo_debugfs_root;
+
+#define SMO_CACHE_NAME "smo_test"
+static struct kmem_cache *cachep;
+
+struct smo_slub_object {
+	struct list_head list;
+	char buf[32];		/* Unused except to control size of object */
+	long id;
+};
+
+/* Our list of allocated objects */
+LIST_HEAD(objects);
+
+static void list_add_to_objects(struct smo_slub_object *so)
+{
+	/*
+	 * We free from the front of the list so store at the
+	 * tail in order to put holes in the cache when we free.
+	 */
+	list_add_tail(&so->list, &objects);
+}
+
+/**
+ * smo_object_ctor() - SMO object constructor function.
+ * @ptr: Pointer to memory where the object should be constructed.
+ */
+void smo_object_ctor(void *ptr)
+{
+	struct smo_slub_object *so = ptr;
+
+	INIT_LIST_HEAD(&so->list);
+	memset(so->buf, 0, sizeof(so->buf));
+	so->id = -1;
+}
+
+/**
+ * smo_cache_migrate() - kmem_cache migrate function.
+ * @cp: kmem_cache pointer.
+ * @objs: Array of pointers to objects to migrate.
+ * @size: Number of objects in @objs.
+ * @node: NUMA node where the object should be allocated.
+ * @private: Pointer returned by kmem_cache_isolate_func().
+ */
+void smo_cache_migrate(struct kmem_cache *cp, void **objs, int size,
+		       int node, void *private)
+{
+	struct smo_slub_object **so_objs = (struct smo_slub_object **)objs;
+	struct smo_slub_object *so_old, *so_new;
+	int i;
+
+	for (i = 0; i < size; i++) {
+		so_old = so_objs[i];
+
+		so_new = kmem_cache_alloc_node(cachep, GFP_KERNEL, node);
+		if (!so_new) {
+			pr_debug("kmem_cache_alloc failed\n");
+			return;
+		}
+
+		/* Copy object */
+		so_new->id = so_old->id;
+
+		/* Update references to old object */
+		list_del(&so_old->list);
+		list_add_to_objects(so_new);
+
+		kmem_cache_free(cachep, so_old);
+	}
+}
+
+static int smo_enable_cache_mobility(int _unused, int __unused)
+{
+	/* Enable movable objects: BOOM! */
+	kmem_cache_setup_mobility(cachep, NULL, smo_cache_migrate);
+	pr_info("smo: kmem_cache %s defrag enabled\n", SMO_CACHE_NAME);
+	return 0;
+}
+
+/*
+ * smo_alloc_objects() - Allocate objects and store reference.
+ * @nr_objs: Number of objects to allocate.
+ * @node: NUMA node to allocate objects on.
+ *
+ * Allocates @n smo_slub_objects.  Stores a reference to them in
+ * the global list of objects (at the tail of the list).
+ *
+ * Return: The number of objects allocated.
+ */
+static int smo_alloc_objects(int nr_objs, int node)
+{
+	struct smo_slub_object *so;
+	int i;
+
+	/* Set sane parameters if no args passed in */
+	if (nr_objs == SMO_CMD_DEFAUT_ARG)
+		nr_objs = 1;
+	if (node == SMO_CMD_DEFAUT_ARG)
+		node = NUMA_NO_NODE;
+
+	for (i = 0; i < nr_objs; i++) {
+		if (node == NUMA_NO_NODE)
+			so = kmem_cache_alloc(cachep, GFP_KERNEL);
+		else
+			so = kmem_cache_alloc_node(cachep, GFP_KERNEL, node);
+		if (!so) {
+			pr_err("smo: Failed to alloc object %d of %d\n", i, nr_objs);
+			return i;
+		}
+		list_add_to_objects(so);
+	}
+	return nr_objs;
+}
+
+/*
+ * smo_free_object() - Frees n objects from position.
+ * @nr_objs: Number of objects to free.
+ * @pos: Position in global list to start freeing.
+ *
+ * Iterates over the global list of objects to position @pos then frees @n
+ * objects from there (or to end of list).  Does nothing if @n > list length.
+ *
+ * Calling with @n==0 frees all objects starting at @pos.
+ *
+ * Return: Number of objects freed.
+ */
+static int smo_free_object(int nr_objs, int pos)
+{
+	struct smo_slub_object *cur, *tmp;
+	int deleted = 0;
+	int i = 0;
+
+	/* Set sane parameters if no args passed in */
+	if (nr_objs == SMO_CMD_DEFAUT_ARG)
+		nr_objs = 1;
+	if (pos == SMO_CMD_DEFAUT_ARG)
+		pos = 0;
+
+	list_for_each_entry_safe(cur, tmp, &objects, list) {
+		if (i < pos) {
+			i++;
+			continue;
+		}
+
+		list_del(&cur->list);
+		kmem_cache_free(cachep, cur);
+		deleted++;
+		if (deleted == nr_objs)
+			break;
+	}
+	return deleted;
+}
+
+static int index_for_expected_id(long *expected, int size, long id)
+{
+	int i;
+
+	/* Array is unsorted, just iterate the whole thing */
+	for (i = 0; i < size; i++) {
+		if (expected[i] == id)
+			return i;
+	}
+	return -1;		/* Not found */
+}
+
+static int assert_have_objects(int nr_objs, int keep)
+{
+	struct smo_slub_object *cur;
+	long *expected;		/* Array of expected IDs */
+	int nr_ids;		/* Length of array */
+	long id;
+	int index, i;
+
+	nr_ids = nr_objs / keep + 1;
+
+	expected = kmalloc_array(nr_ids, sizeof(long), GFP_KERNEL);
+	if (!expected)
+		return -ENOMEM;
+
+	id = 0;
+	for (i = 0; i < nr_ids; i++) {
+		expected[i] = id;
+		id += keep;
+	}
+
+	list_for_each_entry(cur, &objects, list) {
+		index = index_for_expected_id(expected, nr_ids, cur->id);
+		if (index < 0) {
+			pr_err("smo: ID not found: %ld\n", cur->id);
+			return -1;
+		}
+
+		if (expected[index] == -1) {
+			pr_err("smo: ID already encountered: %ld\n", cur->id);
+			return -1;
+		}
+		expected[index] = -1;
+	}
+	return 0;
+}
+
+/*
+ * smo_run_module_tests() - Runs unit tests from within the module
+ * @nr_objs: Number of objects to allocate.
+ * @keep: Free all but 1 in @keep objects.
+ *
+ * Allocates @nr_objects then iterates over the allocated objects
+ * freeing all but 1 out of every @keep objects i.e. for @keep==10
+ * keeps the first object then frees the next 9.
+ *
+ * Caller is responsible for ensuring that the cache has at most a
+ * single slab on the partial list without any objects in it.  This is
+ * easy enough to ensure, just call this when the module is freshly
+ * loaded.
+ */
+static int smo_run_module_tests(int nr_objs, int keep)
+{
+	struct smo_slub_object *so;
+	struct smo_slub_object *cur, *tmp;
+	long i;
+
+	if (!list_empty(&objects)) {
+		pr_err("smo: test requires clean module state\n");
+		return -1;
+	}
+
+	/* Set sane parameters if no args passed in */
+	if (nr_objs == SMO_CMD_DEFAUT_ARG)
+		nr_objs = 1000;
+	if (keep == SMO_CMD_DEFAUT_ARG)
+		keep = 10;
+
+	pr_info("smo: test using nr_objs: %d keep: %d\n", nr_objs, keep);
+
+	/* Perhaps we got called like this 'test 1000' */
+	if (keep == 0) {
+		pr_err("Usage: test <nr_objs> <keep>\n");
+		return -1;
+	}
+
+	/* Test constructor */
+	so = kmem_cache_alloc(cachep, GFP_KERNEL);
+	if (!so) {
+		pr_err("smo: Failed to alloc object\n");
+		return -1;
+	}
+	if (so->id != -1) {
+		pr_err("smo: Initial state incorrect");
+		return -1;
+	}
+	kmem_cache_free(cachep, so);
+
+	/*
+	 * Test that object migration is correctly implemented by module
+	 *
+	 * This gives us confidence that if new code correctly enables
+	 * object migration (via correct implementation of migrate and
+	 * isolate functions) then the slub allocator code that does
+	 * object migration is correct.
+	 */
+
+	for (i = 0; i < nr_objs; i++) {
+		so = kmem_cache_alloc(cachep, GFP_KERNEL);
+		if (!so) {
+			pr_err("smo: Failed to alloc object %ld of %d\n",
+			       i, nr_objs);
+			return -1;
+		}
+		so->id = (long)i;
+		list_add_to_objects(so);
+	}
+
+	assert_have_objects(nr_objs, 1);
+
+	i = 0;
+	list_for_each_entry_safe(cur, tmp, &objects, list) {
+		if (i++ % keep == 0)
+			continue;
+
+		list_del(&cur->list);
+		kmem_cache_free(cachep, cur);
+	}
+
+	/* Verify shrink does nothing when migration is not enabled */
+	kmem_cache_shrink(cachep);
+	assert_have_objects(nr_objs, 1);
+
+	/* Now test shrink */
+	kmem_cache_setup_mobility(cachep, NULL, smo_cache_migrate);
+	kmem_cache_shrink(cachep);
+	/*
+	 * Because of how migrate function deletes and adds objects to
+	 * the objects list we have no way of knowing the order.  We
+	 * want to confirm that we have all the objects after shrink
+	 * that we had before we did the shrink.
+	 */
+	assert_have_objects(nr_objs, keep);
+
+	/* cleanup */
+	list_for_each_entry_safe(cur, tmp, &objects, list) {
+		list_del(&cur->list);
+		kmem_cache_free(cachep, cur);
+	}
+	kmem_cache_shrink(cachep); /* Remove empty slabs from partial list */
+
+	pr_info("smo: Module tests completed successfully\n");
+	return 0;
+}
+
+/*
+ * struct functions() - Map command to a function pointer.
+ */
+struct functions {
+	char *fn_name;
+	int (*fn_ptr)(int arg0, int arg1);
+} fn_tab[] = {
+	/*
+	 * Because of the way we parse the function table no command
+	 * may have another command as its prefix.
+	 *  i.e. this will break: 'foo'  and 'foobar'
+	 */
+	{"enable", smo_enable_cache_mobility},
+	{"alloc", smo_alloc_objects},
+	{"free", smo_free_object},
+	{"test", smo_run_module_tests},
+};
+
+#define FN_TAB_SIZE (sizeof(fn_tab) / sizeof(struct functions))
+
+/*
+ * parse_cmd_buf() - Gets command and arguments command string.
+ * @buf: Buffer containing the command string.
+ * @cmd: Out parameter, pointer to the command.
+ * @arg1: Out parameter, stores the first argument.
+ * @arg2: Out parameter, stores the second argument.
+ *
+ * Parses and tokenizes the input command buffer. Stores a pointer to the
+ * command (start of @buf) in @cmd.  Stores the converted long values for
+ * argument 1 and 2 in the respective out parameters @arg1 and @arg2.
+ *
+ * Since arguments are optional, if they are not found the default values are
+ * returned.  In order for the caller to differentiate defaults from arguments
+ * of the same value the number of arguments parsed is returned.
+ *
+ * Return: Number of arguments found.
+ */
+static int parse_cmd_buf(char *buf, char **cmd, long *arg1, long *arg2)
+{
+	int found;
+	char *ptr;
+	int ret;
+
+	*arg1 = SMO_CMD_DEFAUT_ARG;
+	*arg2 = SMO_CMD_DEFAUT_ARG;
+	found = 0;
+
+	/* Jump over the command, check if there are any args */
+	ptr = strsep(&buf, " ");
+	if (!ptr || !buf)
+		return found;
+
+	ptr = strsep(&buf, " ");
+	ret = kstrtol(ptr, 10, arg1);
+	if (ret < 0) {
+		pr_err("failed to convert arg, defaulting to %d. (%s)\n",
+		       SMO_CMD_DEFAUT_ARG, ptr);
+		return found;
+	}
+	found++;
+	if (!buf)		/* No second arg */
+		return found;
+
+	ptr = strsep(&buf, " ");
+	ret = kstrtol(ptr, 10, arg2);
+	if (ret < 0) {
+		pr_err("failed to convert arg, defaulting to %d. (%s)\n",
+		       SMO_CMD_DEFAUT_ARG, ptr);
+		return found;
+	}
+	found++;
+
+	return found;
+}
+
+/*
+ * call_function() - Calls the function described by str.
+ * @str: '<cmd> [<arg>]'
+ *
+ * Does table lookup on <cmd>, calls appropriate function passing
+ * <arg> as a the argument.  Optional arg defaults to 1.
+ */
+static void call_function(char *str)
+{
+	char *cmd;
+	long arg1 = 0;
+	long arg2 = 0;
+	int i;
+
+	if (!str)
+		return;
+
+	(void)parse_cmd_buf(str, &cmd, &arg1, &arg2);
+
+	for (i = 0; i < FN_TAB_SIZE; i++) {
+		char *fn_name = fn_tab[i].fn_name;
+
+		if (strcmp(fn_name, str) == 0) {
+			fn_tab[i].fn_ptr(arg1, arg2);
+			return;	/* All done */
+		}
+	}
+
+	pr_err("failed to call function for cmd: %s\n", str);
+}
+
+/*
+ * smo_callfn_debugfs_write() - debugfs write function.
+ * @file: User file
+ * @user_buf: Userspace buffer
+ * @len: Length of the user space buffer
+ * @off: Offset within the file
+ *
+ * Used for triggering functions by writing command to debugfs file.
+ *
+ *   echo '<cmd> <arg>'  > /sys/kernel/debug/smo/callfn
+ *
+ * Return: Number of bytes copied if request succeeds,
+ *	   the corresponding error code otherwise.
+ */
+static ssize_t smo_callfn_debugfs_write(struct file *file,
+					const char __user *ubuf,
+					size_t len,
+					loff_t *off)
+{
+	char *kbuf;
+	int nbytes = 0;
+
+	if (*off != 0 || len == 0)
+		return -EINVAL;
+
+	kbuf = kzalloc(len, GFP_KERNEL);
+	if (!kbuf)
+		return -ENOMEM;
+
+	nbytes = strncpy_from_user(kbuf, ubuf, len);
+	if (nbytes < 0)
+		goto out;
+
+	if (kbuf[nbytes - 1] == '\n')
+		kbuf[nbytes - 1] = '\0';
+
+	call_function(kbuf);	/* Tokenizes kbuf */
+out:
+	kfree(kbuf);
+	return nbytes;
+}
+
+const struct file_operations fops_callfn_debugfs = {
+	.owner = THIS_MODULE,
+	.write = smo_callfn_debugfs_write,
+};
+
+static int __init smo_debugfs_init(void)
+{
+	struct dentry *d;
+
+	smo_debugfs_root = debugfs_create_dir(SMO_DEBUGFS_DIR, NULL);
+	d = debugfs_create_file("callfn", 0200, smo_debugfs_root, NULL,
+				&fops_callfn_debugfs);
+	if (IS_ERR(d))
+		return PTR_ERR(d);
+
+	return 0;
+}
+
+static void __exit smo_debugfs_cleanup(void)
+{
+	debugfs_remove_recursive(smo_debugfs_root);
+}
+
+static int __init smo_cache_init(void)
+{
+	cachep = kmem_cache_create(SMO_CACHE_NAME,
+				   sizeof(struct smo_slub_object),
+				   0, 0, smo_object_ctor);
+	if (!cachep)
+		return -1;
+
+	return 0;
+}
+
+static void __exit smo_cache_cleanup(void)
+{
+	struct smo_slub_object *cur, *tmp;
+
+	list_for_each_entry_safe(cur, tmp, &objects, list) {
+		list_del(&cur->list);
+		kmem_cache_free(cachep, cur);
+	}
+	kmem_cache_destroy(cachep);
+}
+
+static int __init smo_init(void)
+{
+	int ret;
+
+	ret = smo_cache_init();
+	if (ret) {
+		pr_err("smo: Failed to create cache\n");
+		return ret;
+	}
+	pr_info("smo: Created kmem_cache: %s\n", SMO_CACHE_NAME);
+
+	ret = smo_debugfs_init();
+	if (ret) {
+		pr_err("smo: Failed to init debugfs\n");
+		return ret;
+	}
+	pr_info("smo: Created debugfs directory: /sys/kernel/debugfs/%s\n",
+		SMO_DEBUGFS_DIR);
+
+	pr_info("smo: Test module loaded\n");
+	return 0;
+}
+module_init(smo_init);
+
+static void __exit smo_exit(void)
+{
+	smo_debugfs_cleanup();
+	smo_cache_cleanup();
+
+	pr_info("smo: Test module removed\n");
+}
+module_exit(smo_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Tobin C. Harding");
+MODULE_DESCRIPTION("SLUB Movable Objects test module.");
-- 
2.21.0

[RFC PATCH v5 08/16] tools/testing/slab: Add object migration test suite

[Tobin C. Harding]

We just added a module that enables testing the SLUB allocators ability
to defrag/shrink caches via movable objects.  Tests are better when they
are automated.

Add automated testing via a python script for SLUB movable objects.

Example output:

  $ cd path/to/linux/tools/testing/slab
  $ /slub_defrag.py
  Please run script as root

  $ sudo ./slub_defrag.py
  <test are quiet, no output on success>

  $ sudo ./slub_defrag.py --debug
  Loading module ...
  Slab cache smo_test created
  Objects per slab: 20
  Running sanity checks ...

  Running module stress test (see dmesg for additional test output) ...
  Removing module slub_defrag ...
  Loading module ...
  Slab cache smo_test created

  Running test non-movable ...
  testing slab 'smo_test' prior to enabling movable objects ...
  verified non-movable slabs are NOT shrinkable

  Running test movable ...
  testing slab 'smo_test' after enabling movable objects ...
  verified movable slabs are shrinkable

  Removing module slub_defrag ...

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 tools/testing/slab/slub_defrag.c  |   1 +
 tools/testing/slab/slub_defrag.py | 451 ++++++++++++++++++++++++++++++
 2 files changed, 452 insertions(+)
 create mode 100755 tools/testing/slab/slub_defrag.py

diff --git a/tools/testing/slab/slub_defrag.c b/tools/testing/slab/slub_defrag.c
index 4a5c24394b96..8332e69ee868 100644
--- a/tools/testing/slab/slub_defrag.c
+++ b/tools/testing/slab/slub_defrag.c
@@ -337,6 +337,7 @@ static int smo_run_module_tests(int nr_objs, int keep)
 
 /*
  * struct functions() - Map command to a function pointer.
+ * If you update this please update the documentation in slub_defrag.py
  */
 struct functions {
 	char *fn_name;
diff --git a/tools/testing/slab/slub_defrag.py b/tools/testing/slab/slub_defrag.py
new file mode 100755
index 000000000000..41747c0db39b
--- /dev/null
+++ b/tools/testing/slab/slub_defrag.py
@@ -0,0 +1,451 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import subprocess
+import sys
+from os import path
+
+# SLUB Movable Objects test suite.
+#
+# Requirements:
+#  - CONFIG_SLUB=y
+#  - CONFIG_SLUB_DEBUG=y
+#  - The slub_defrag module in this directory.
+
+# Test SMO using a kernel module that enables triggering arbitrary
+# kernel code from userspace via a debugfs file.
+#
+# Module code is in ./slub_defrag.c, basically the functionality is as
+# follows:
+#
+#  - Creates debugfs file /sys/kernel/debugfs/smo/callfn
+#  - Writes to 'callfn' are parsed as a command string and the function
+#    associated with command is called.
+#  - Defines 4 commands (all commands operate on smo_test cache):
+#     - 'test': Runs module stress tests.
+#     - 'alloc N': Allocates N slub objects
+#     - 'free N POS': Frees N objects starting at POS (see below)
+#     - 'enable': Enables SLUB Movable Objects
+#
+# The module maintains a list of allocated objects.  Allocation adds
+# objects to the tail of the list.  Free'ing frees from the head of the
+# list.  This has the effect of creating free slots in the slab.  For
+# finer grained control over where in the cache slots are free'd POS
+# (position) argument may be used.
+
+# The main() function is reasonably readable; the test suite does the
+# following:
+#
+# 1. Runs the module stress tests.
+# 2. Tests the cache without movable objects enabled.
+#    - Creates multiple partial slabs as explained above.
+#    - Verifies that partial slabs are _not_ removed by shrink (see below).
+# 3. Tests the cache with movable objects enabled.
+#    - Creates multiple partial slabs as explained above.
+#    - Verifies that partial slabs _are_ removed by shrink (see below).
+
+# The sysfs file /sys/kernel/slab/<cache>/shrink enables calling the
+# function kmem_cache_shrink() (see mm/slab_common.c and mm/slub.cc).
+# Shrinking a cache attempts to consolidate all partial slabs by moving
+# objects if object migration is enable for the cache, otherwise
+# shrinking a cache simply re-orders the partial list so as most densely
+# populated slab are at the head of the list.
+
+# Enable/disable debugging output (also enabled via -d | --debug).
+debug = False
+
+# Used in debug messages and when running `insmod`.
+MODULE_NAME = "slub_defrag"
+
+# Slab cache created by the test module.
+CACHE_NAME = "smo_test"
+
+# Set by get_slab_config()
+objects_per_slab = 0
+pages_per_slab = 0
+debugfs_mounted = False         # Set to true if we mount debugfs.
+
+
+def eprint(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+
+def dprint(*args, **kwargs):
+    if debug:
+        print(*args, file=sys.stderr, **kwargs)
+
+
+def run_shell(cmd):
+    return subprocess.call([cmd], shell=True)
+
+
+def run_shell_get_stdout(cmd):
+    return subprocess.check_output([cmd], shell=True)
+
+
+def assert_root():
+    user = run_shell_get_stdout('whoami')
+    if user != b'root\n':
+        eprint("Please run script as root")
+        sys.exit(1)
+
+
+def mount_debugfs():
+    mounted = False
+
+    # Check if debugfs is mounted at a known mount point.
+    ret = run_shell('mount -l | grep /sys/kernel/debug > /dev/null 2>&1')
+    if ret != 0:
+        run_shell('mount -t debugfs none /sys/kernel/debug/')
+        mounted = True
+        dprint("Mounted debugfs on /sys/kernel/debug")
+
+    return mounted
+
+
+def umount_debugfs():
+    dprint("Un-mounting debugfs")
+    run_shell('umount /sys/kernel/debug')
+
+
+def load_module():
+    """Loads the test module.
+
+    We need a clean slab state to start with so module must
+    be loaded by the test suite.
+    """
+    ret = run_shell('lsmod | grep %s > /dev/null' % MODULE_NAME)
+    if ret == 0:
+        eprint("Please unload slub_defrag module before running test suite")
+        return -1
+
+    dprint('Loading module ...')
+    ret = run_shell('insmod %s.ko' % MODULE_NAME)
+    if ret != 0:                # ret==1 on error
+        return -1
+
+    dprint("Slab cache %s created" % CACHE_NAME)
+    return 0
+
+
+def unload_module():
+    ret = run_shell('lsmod | grep %s > /dev/null' % MODULE_NAME)
+    if ret == 0:
+        dprint('Removing module %s ...' % MODULE_NAME)
+        run_shell('rmmod %s > /dev/null 2>&1' % MODULE_NAME)
+
+
+def get_sysfs_value(filename):
+    """
+    Parse slab sysfs files (single line: '20 N0=20')
+    """
+    path = '/sys/kernel/slab/smo_test/%s' % filename
+    f = open(path, "r")
+    s = f.readline()
+    tokens = s.split(" ")
+
+    return int(tokens[0])
+
+
+def get_nr_objects_active():
+    return get_sysfs_value('objects')
+
+
+def get_nr_objects_total():
+    return get_sysfs_value('total_objects')
+
+
+def get_nr_slabs_total():
+    return get_sysfs_value('slabs')
+
+
+def get_nr_slabs_partial():
+    return get_sysfs_value('partial')
+
+
+def get_nr_slabs_full():
+    return get_nr_slabs_total() - get_nr_slabs_partial()
+
+
+def get_slab_config():
+    """Get relevant information from sysfs."""
+    global objects_per_slab
+
+    objects_per_slab = get_sysfs_value('objs_per_slab')
+    if objects_per_slab < 0:
+        return -1
+
+    dprint("Objects per slab: %d" % objects_per_slab)
+    return 0
+
+
+def verify_state(nr_objects_active, nr_objects_total,
+                 nr_slabs_partial, nr_slabs_full, nr_slabs_total, msg=''):
+    err = 0
+    got_nr_objects_active = get_nr_objects_active()
+    got_nr_objects_total = get_nr_objects_total()
+    got_nr_slabs_partial = get_nr_slabs_partial()
+    got_nr_slabs_full = get_nr_slabs_full()
+    got_nr_slabs_total = get_nr_slabs_total()
+
+    if got_nr_objects_active != nr_objects_active:
+        err = -1
+
+    if got_nr_objects_total != nr_objects_total:
+        err = -2
+
+    if got_nr_slabs_partial != nr_slabs_partial:
+        err = -3
+
+    if got_nr_slabs_full != nr_slabs_full:
+        err = -4
+
+    if got_nr_slabs_total != nr_slabs_total:
+        err = -5
+
+    if err != 0:
+        dprint("Verify state: %s" % msg)
+        dprint("  what\t\t\twant\tgot")
+        dprint("-----------------------------------------")
+        dprint("  %s\t%d\t%d" % ('nr_objects_active', nr_objects_active, got_nr_objects_active))
+        dprint("  %s\t%d\t%d" % ('nr_objects_total', nr_objects_total, got_nr_objects_total))
+        dprint("  %s\t%d\t%d" % ('nr_slabs_partial', nr_slabs_partial, got_nr_slabs_partial))
+        dprint("  %s\t\t%d\t%d" % ('nr_slabs_full', nr_slabs_full, got_nr_slabs_full))
+        dprint("  %s\t%d\t%d\n" % ('nr_slabs_total', nr_slabs_total, got_nr_slabs_total))
+
+    return err
+
+
+def exec_via_sysfs(command):
+        ret = run_shell('echo %s > /sys/kernel/debug/smo/callfn' % command)
+        if ret != 0:
+            eprint("Failed to echo command to sysfs: %s" % command)
+
+        return ret
+
+
+def enable_movable_objects():
+    return exec_via_sysfs('enable')
+
+
+def alloc(n):
+    exec_via_sysfs("alloc %d" % n)
+
+
+def free(n, pos = 0):
+    exec_via_sysfs('free %d %d' % (n, pos))
+
+
+def shrink():
+    ret = run_shell('slabinfo smo_test -s')
+    if ret != 0:
+            eprint("Failed to execute slabinfo -s")
+
+
+def sanity_checks():
+    # Verify everything is 0 to start with.
+    return verify_state(0, 0, 0, 0, 0, "sanity check")
+
+
+def test_non_movable():
+    one_over = objects_per_slab + 1
+
+    dprint("testing slab 'smo_test' prior to enabling movable objects ...")
+
+    alloc(one_over)
+
+    objects_active = one_over
+    objects_total = objects_per_slab * 2
+    slabs_partial = 1
+    slabs_full = 1
+    slabs_total = 2
+    ret = verify_state(objects_active, objects_total,
+                       slabs_partial, slabs_full, slabs_total,
+                       "non-movable: initial allocation")
+    if ret != 0:
+        eprint("test_non_movable: failed to verify initial state")
+        return -1
+
+    # Free object from first slot of first slab.
+    free(1)
+    objects_active = one_over - 1
+    objects_total = objects_per_slab * 2
+    slabs_partial = 2
+    slabs_full = 0
+    slabs_total = 2
+    ret = verify_state(objects_active, objects_total,
+                       slabs_partial, slabs_full, slabs_total,
+                       "non-movable: after free")
+    if ret != 0:
+        eprint("test_non_movable: failed to verify after free")
+        return -1
+
+    # Non-movable cache, shrink should have no effect.
+    shrink()
+    ret = verify_state(objects_active, objects_total,
+                       slabs_partial, slabs_full, slabs_total,
+                       "non-movable: after shrink")
+    if ret != 0:
+        eprint("test_non_movable: failed to verify after shrink")
+        return -1
+
+    # Cleanup
+    free(objects_per_slab)
+    shrink()
+
+    dprint("verified non-movable slabs are NOT shrinkable")
+    return 0
+
+
+def test_movable():
+    one_over = objects_per_slab + 1
+
+    dprint("testing slab 'smo_test' after enabling movable objects ...")
+
+    alloc(one_over)
+
+    objects_active = one_over
+    objects_total = objects_per_slab * 2
+    slabs_partial = 1
+    slabs_full = 1
+    slabs_total = 2
+    ret = verify_state(objects_active, objects_total,
+                       slabs_partial, slabs_full, slabs_total,
+                       "movable: initial allocation")
+    if ret != 0:
+        eprint("test_movable: failed to verify initial state")
+        return -1
+
+    # Free object from first slot of first slab.
+    free(1)
+    objects_active = one_over - 1
+    objects_total = objects_per_slab * 2
+    slabs_partial = 2
+    slabs_full = 0
+    slabs_total = 2
+    ret = verify_state(objects_active, objects_total,
+                       slabs_partial, slabs_full, slabs_total,
+                       "movable: after free")
+    if ret != 0:
+        eprint("test_movable: failed to verify after free")
+        return -1
+
+    # movable cache, shrink should move objects and free slab.
+    shrink()
+    objects_active = one_over - 1
+    objects_total = objects_per_slab * 1
+    slabs_partial = 0
+    slabs_full = 1
+    slabs_total = 1
+    ret = verify_state(objects_active, objects_total,
+                       slabs_partial, slabs_full, slabs_total,
+                       "movable: after shrink")
+    if ret != 0:
+        eprint("test_movable: failed to verify after shrink")
+        return -1
+
+    # Cleanup
+    free(objects_per_slab)
+    shrink()
+
+    dprint("verified movable slabs are shrinkable")
+    return 0
+
+
+def dprint_start_test(test):
+    dprint("Running %s ..." % test)
+
+
+def dprint_done():
+    dprint("")
+
+
+def run_test(fn, desc):
+    dprint_start_test(desc)
+    ret = fn()
+    if ret < 0:
+        fail_test(desc)
+    dprint_done()
+
+
+# Load and unload the module for this test to ensure clean state.
+def run_module_stress_test():
+    dprint("Running module stress test (see dmesg for additional test output) ...")
+
+    unload_module()
+    ret = load_module()
+    if ret < 0:
+        cleanup_and_exit(ret)
+
+    exec_via_sysfs("test");
+
+    unload_module()
+
+    dprint()
+
+
+def fail_test(msg):
+    eprint("\nFAIL: test failed: '%s' ... aborting\n" % msg)
+    cleanup_and_exit(1)
+
+
+def display_help():
+    print("Usage: %s [OPTIONS]\n" % path.basename(sys.argv[0]))
+    print("\tRuns defrag test suite (a.k.a. SLUB Movable Objects)\n")
+    print("OPTIONS:")
+    print("\t-d | --debug       Enable verbose debug output")
+    print("\t-h | --help        Print this help and exit")
+
+
+def cleanup_and_exit(return_code):
+    global debugfs_mounted
+
+    if debugfs_mounted == True:
+        umount_debugfs()
+
+    unload_module()
+
+    sys.exit(return_code)
+
+
+def main():
+    global debug
+
+    if len(sys.argv) > 1:
+        if sys.argv[1] == '-h' or sys.argv[1] == '--help':
+            display_help()
+            sys.exit(0)
+
+        if sys.argv[1] == '-d' or sys.argv[1] == '--debug':
+            debug = True
+
+    assert_root()
+
+    # Use cleanup_and_exit() instead of sys.exit() after mounting debugfs.
+    debugfs_mounted = mount_debugfs()
+
+    # Loads and unloads the module.
+    run_module_stress_test()
+
+    ret = load_module()
+    if (ret < 0):
+        cleanup_and_exit(ret)
+
+    ret = get_slab_config()
+    if (ret != 0):
+        fail_test("get slab config details")
+
+    run_test(sanity_checks, "sanity checks")
+
+    run_test(test_non_movable, "test non-movable")
+
+    ret = enable_movable_objects()
+    if (ret != 0):
+        fail_test("enable movable objects")
+
+    run_test(test_movable, "test movable")
+
+    cleanup_and_exit(0)
+
+if __name__== "__main__":
+  main()
-- 
2.21.0

[RFC PATCH v5 09/16] lib: Separate radix_tree_node and xa_node slab cache

[Tobin C. Harding]

Earlier, Slab Movable Objects (SMO) was implemented.  The XArray is now
able to take advantage of SMO in order to make xarray nodes
movable (when using the SLUB allocator).

Currently the radix tree uses the same slab cache as the XArray.  Only
XArray nodes are movable _not_ radix tree nodes.  We can give the radix
tree its own slab cache to overcome this.

In preparation for implementing XArray object migration (xa_node
objects) via Slab Movable Objects add a slab cache solely for XArray
nodes and make the XArray use this slab cache instead of the
radix_tree_node slab cache.

Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 include/linux/xarray.h |  3 +++
 init/main.c            |  2 ++
 lib/radix-tree.c       |  2 +-
 lib/xarray.c           | 48 ++++++++++++++++++++++++++++++++++--------
 4 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 0e01e6129145..773f91f8e1db 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -42,6 +42,9 @@
 
 #define BITS_PER_XA_VALUE	(BITS_PER_LONG - 1)
 
+/* Called from init/main.c */
+void xarray_slabcache_init(void);
+
 /**
  * xa_mk_value() - Create an XArray entry from an integer.
  * @v: Value to store in XArray.
diff --git a/init/main.c b/init/main.c
index 5a2c69b4d7b3..e89915ffbe26 100644
--- a/init/main.c
+++ b/init/main.c
@@ -106,6 +106,7 @@ static int kernel_init(void *);
 
 extern void init_IRQ(void);
 extern void radix_tree_init(void);
+extern void xarray_slabcache_init(void);
 
 /*
  * Debug helper: via this flag we know that we are in 'early bootup code'
@@ -621,6 +622,7 @@ asmlinkage __visible void __init start_kernel(void)
 		 "Interrupts were enabled *very* early, fixing it\n"))
 		local_irq_disable();
 	radix_tree_init();
+	xarray_slabcache_init();
 
 	/*
 	 * Set up housekeeping before setting up workqueues to allow the unbound
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 14d51548bea6..edbfb530ba73 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -44,7 +44,7 @@
 /*
  * Radix tree node cache.
  */
-struct kmem_cache *radix_tree_node_cachep;
+static struct kmem_cache *radix_tree_node_cachep;
 
 /*
  * The radix tree is variable-height, so an insert operation not only has
diff --git a/lib/xarray.c b/lib/xarray.c
index 6be3acbb861f..a528a5277c9d 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -27,6 +27,8 @@
  * @entry refers to something stored in a slot in the xarray
  */
 
+static struct kmem_cache *xa_node_cachep;
+
 static inline unsigned int xa_lock_type(const struct xarray *xa)
 {
 	return (__force unsigned int)xa->xa_flags & 3;
@@ -244,9 +246,21 @@ void *xas_load(struct xa_state *xas)
 }
 EXPORT_SYMBOL_GPL(xas_load);
 
-/* Move the radix tree node cache here */
-extern struct kmem_cache *radix_tree_node_cachep;
-extern void radix_tree_node_rcu_free(struct rcu_head *head);
+void xa_node_rcu_free(struct rcu_head *head)
+{
+	struct xa_node *node = container_of(head, struct xa_node, rcu_head);
+
+	/*
+	 * Must only free zeroed nodes into the slab.  We can be left with
+	 * non-NULL entries by radix_tree_free_nodes, so clear the entries
+	 * and tags here.
+	 */
+	memset(node->slots, 0, sizeof(node->slots));
+	memset(node->tags, 0, sizeof(node->tags));
+	INIT_LIST_HEAD(&node->private_list);
+
+	kmem_cache_free(xa_node_cachep, node);
+}
 
 #define XA_RCU_FREE	((struct xarray *)1)
 
@@ -254,7 +268,7 @@ static void xa_node_free(struct xa_node *node)
 {
 	XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
 	node->array = XA_RCU_FREE;
-	call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
+	call_rcu(&node->rcu_head, xa_node_rcu_free);
 }
 
 /*
@@ -270,7 +284,7 @@ static void xas_destroy(struct xa_state *xas)
 	if (!node)
 		return;
 	XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
-	kmem_cache_free(radix_tree_node_cachep, node);
+	kmem_cache_free(xa_node_cachep, node);
 	xas->xa_alloc = NULL;
 }
 
@@ -298,7 +312,7 @@ bool xas_nomem(struct xa_state *xas, gfp_t gfp)
 		xas_destroy(xas);
 		return false;
 	}
-	xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
+	xas->xa_alloc = kmem_cache_alloc(xa_node_cachep, gfp);
 	if (!xas->xa_alloc)
 		return false;
 	XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
@@ -327,10 +341,10 @@ static bool __xas_nomem(struct xa_state *xas, gfp_t gfp)
 	}
 	if (gfpflags_allow_blocking(gfp)) {
 		xas_unlock_type(xas, lock_type);
-		xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
+		xas->xa_alloc = kmem_cache_alloc(xa_node_cachep, gfp);
 		xas_lock_type(xas, lock_type);
 	} else {
-		xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
+		xas->xa_alloc = kmem_cache_alloc(xa_node_cachep, gfp);
 	}
 	if (!xas->xa_alloc)
 		return false;
@@ -358,7 +372,7 @@ static void *xas_alloc(struct xa_state *xas, unsigned int shift)
 	if (node) {
 		xas->xa_alloc = NULL;
 	} else {
-		node = kmem_cache_alloc(radix_tree_node_cachep,
+		node = kmem_cache_alloc(xa_node_cachep,
 					GFP_NOWAIT | __GFP_NOWARN);
 		if (!node) {
 			xas_set_err(xas, -ENOMEM);
@@ -1971,6 +1985,22 @@ void xa_destroy(struct xarray *xa)
 }
 EXPORT_SYMBOL(xa_destroy);
 
+static void xa_node_ctor(void *arg)
+{
+	struct xa_node *node = arg;
+
+	memset(node, 0, sizeof(*node));
+	INIT_LIST_HEAD(&node->private_list);
+}
+
+void __init xarray_slabcache_init(void)
+{
+	xa_node_cachep = kmem_cache_create("xarray_node",
+					   sizeof(struct xa_node), 0,
+					   SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
+					   xa_node_ctor);
+}
+
 #ifdef XA_DEBUG
 void xa_dump_node(const struct xa_node *node)
 {
-- 
2.21.0

[RFC PATCH v5 10/16] xarray: Implement migration function for xa_node objects

[Tobin C. Harding]

Recently Slab Movable Objects (SMO) was implemented for the SLUB
allocator.  The XArray can take advantage of this and make the xa_node
slab cache objects movable.

Implement functions to migrate objects and activate SMO when we
initialise the XArray slab cache.

This is based on initial code by Matthew Wilcox and was modified to work
with slab object migration.

Cc: Matthew Wilcox <willy@infradead.org>
Co-developed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 lib/xarray.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/lib/xarray.c b/lib/xarray.c
index a528a5277c9d..c6b077f59e88 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1993,12 +1993,73 @@ static void xa_node_ctor(void *arg)
 	INIT_LIST_HEAD(&node->private_list);
 }
 
+static void xa_object_migrate(struct xa_node *node, int numa_node)
+{
+	struct xarray *xa = READ_ONCE(node->array);
+	void __rcu **slot;
+	struct xa_node *new_node;
+	int i;
+
+	/* Freed or not yet in tree then skip */
+	if (!xa || xa == XA_RCU_FREE)
+		return;
+
+	new_node = kmem_cache_alloc_node(xa_node_cachep, GFP_KERNEL, numa_node);
+	if (!new_node) {
+		pr_err("%s: slab cache allocation failed\n", __func__);
+		return;
+	}
+
+	xa_lock_irq(xa);
+
+	/* Check again..... */
+	if (xa != node->array) {
+		node = new_node;
+		goto unlock;
+	}
+
+	memcpy(new_node, node, sizeof(struct xa_node));
+
+	if (list_empty(&node->private_list))
+		INIT_LIST_HEAD(&new_node->private_list);
+	else
+		list_replace(&node->private_list, &new_node->private_list);
+
+	for (i = 0; i < XA_CHUNK_SIZE; i++) {
+		void *x = xa_entry_locked(xa, new_node, i);
+
+		if (xa_is_node(x))
+			rcu_assign_pointer(xa_to_node(x)->parent, new_node);
+	}
+	if (!new_node->parent)
+		slot = &xa->xa_head;
+	else
+		slot = &xa_parent_locked(xa, new_node)->slots[new_node->offset];
+	rcu_assign_pointer(*slot, xa_mk_node(new_node));
+
+unlock:
+	xa_unlock_irq(xa);
+	xa_node_free(node);
+	rcu_barrier();
+}
+
+static void xa_migrate(struct kmem_cache *s, void **objects, int nr,
+		       int node, void *_unused)
+{
+	int i;
+
+	for (i = 0; i < nr; i++)
+		xa_object_migrate(objects[i], node);
+}
+
+
 void __init xarray_slabcache_init(void)
 {
 	xa_node_cachep = kmem_cache_create("xarray_node",
 					   sizeof(struct xa_node), 0,
 					   SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
 					   xa_node_ctor);
+	kmem_cache_setup_mobility(xa_node_cachep, NULL, xa_migrate);
 }
 
 #ifdef XA_DEBUG
-- 
2.21.0

[RFC PATCH v5 11/16] tools/testing/slab: Add XArray movable objects tests

[Tobin C. Harding]

We just implemented movable objects for the XArray.  Let's test it
intree.

Add test module for the XArray's movable objects implementation.

Functionality of the XArray Slab Movable Object implementation can
usually be seen by simply by using `slabinfo` on a running machine since
the radix tree is typically in use on a running machine and will have
partial slabs.  For repeated testing we can use the test module to run
to simulate a workload on the XArray then use `slabinfo` to test object
migration is functioning.

If testing on freshly spun up VM (low radix tree workload) it may be
necessary to load/unload the module a number of times to create partial
slabs.

Example test session
--------------------

Relevant /proc/slabinfo column headers:

  name   <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab>

Prior to testing slabinfo report for radix_tree_node:

  # slabinfo radix_tree_node --report

  Slabcache: radix_tree_node  Aliases:  0 Order :  2 Objects: 8352
  ** Reclaim accounting active
  ** Defragmentation at 30%

  Sizes (bytes)     Slabs              Debug                Memory
  ------------------------------------------------------------------------
  Object :     576  Total  :     497   Sanity Checks : On   Total: 8142848
  SlabObj:     912  Full   :     473   Redzoning     : On   Used : 4810752
  SlabSiz:   16384  Partial:      24   Poisoning     : On   Loss : 3332096
  Loss   :     336  CpuSlab:       0   Tracking      : On   Lalig: 2806272
  Align  :       8  Objects:      17   Tracing       : Off  Lpadd:  437360

Here you can see the kernel was built with Slab Movable Objects enabled
for the XArray (XArray uses the radix tree below the surface).

After inserting the test module (note we have triggered allocation of a
number of radix tree nodes increasing the object count but decreasing the
number of partial slabs):

  # slabinfo radix_tree_node --report

  Slabcache: radix_tree_node  Aliases:  0 Order :  2 Objects: 8442
  ** Reclaim accounting active
  ** Defragmentation at 30%

  Sizes (bytes)     Slabs              Debug                Memory
  ------------------------------------------------------------------------
  Object :     576  Total  :     499   Sanity Checks : On   Total: 8175616
  SlabObj:     912  Full   :     484   Redzoning     : On   Used : 4862592
  SlabSiz:   16384  Partial:      15   Poisoning     : On   Loss : 3313024
  Loss   :     336  CpuSlab:       0   Tracking      : On   Lalig: 2836512
  Align  :       8  Objects:      17   Tracing       : Off  Lpadd:  439120

Now we can shrink the radix_tree_node cache:

  # slabinfo radix_tree_node --shrink
  # slabinfo radix_tree_node --report

  Slabcache: radix_tree_node  Aliases:  0 Order :  2 Objects: 8515
  ** Reclaim accounting active
  ** Defragmentation at 30%

  Sizes (bytes)     Slabs              Debug                Memory
  ------------------------------------------------------------------------
  Object :     576  Total  :     501   Sanity Checks : On   Total: 8208384
  SlabObj:     912  Full   :     500   Redzoning     : On   Used : 4904640
  SlabSiz:   16384  Partial:       1   Poisoning     : On   Loss : 3303744
  Loss   :     336  CpuSlab:       0   Tracking      : On   Lalig: 2861040
  Align  :       8  Objects:      17   Tracing       : Off  Lpadd:  440880

Note the single remaining partial slab.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 tools/testing/slab/Makefile             |   2 +-
 tools/testing/slab/slub_defrag_xarray.c | 211 ++++++++++++++++++++++++
 2 files changed, 212 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/slab/slub_defrag_xarray.c

diff --git a/tools/testing/slab/Makefile b/tools/testing/slab/Makefile
index 440c2e3e356f..44c18d9a4d52 100644
--- a/tools/testing/slab/Makefile
+++ b/tools/testing/slab/Makefile
@@ -1,4 +1,4 @@
-obj-m += slub_defrag.o
+obj-m += slub_defrag.o slub_defrag_xarray.o
 
 KTREE=../../..
 
diff --git a/tools/testing/slab/slub_defrag_xarray.c b/tools/testing/slab/slub_defrag_xarray.c
new file mode 100644
index 000000000000..41143f73256c
--- /dev/null
+++ b/tools/testing/slab/slub_defrag_xarray.c
@@ -0,0 +1,211 @@
+// SPDX-License-Identifier: GPL-2.0+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+#include <linux/list.h>
+#include <linux/gfp.h>
+#include <linux/xarray.h>
+
+#define SMOX_CACHE_NAME "smox_test"
+static struct kmem_cache *cachep;
+
+/*
+ * Declare XArrays globally so we can clean them up on module unload.
+ */
+
+/* Used by test_smo_xarray()*/
+DEFINE_XARRAY(things);
+
+/* Thing to store pointers to in the XArray */
+struct smox_thing {
+	long id;
+};
+
+/* It's up to the caller to ensure id is unique */
+static struct smox_thing *alloc_thing(int id)
+{
+	struct smox_thing *thing;
+
+	thing = kmem_cache_alloc(cachep, GFP_KERNEL);
+	if (!thing)
+		return ERR_PTR(-ENOMEM);
+
+	thing->id = id;
+	return thing;
+}
+
+/**
+ * smox_object_ctor() - SMO object constructor function.
+ * @ptr: Pointer to memory where the object should be constructed.
+ */
+void smox_object_ctor(void *ptr)
+{
+	struct smox_thing *thing = ptr;
+
+	thing->id = -1;
+}
+
+/**
+ * smox_cache_migrate() - kmem_cache migrate function.
+ * @cp: kmem_cache pointer.
+ * @objs: Array of pointers to objects to migrate.
+ * @size: Number of objects in @objs.
+ * @node: NUMA node where the object should be allocated.
+ * @private: Pointer returned by kmem_cache_isolate_func().
+ */
+void smox_cache_migrate(struct kmem_cache *cp, void **objs, int size,
+			int node, void *private)
+{
+	struct smox_thing **ptrs = (struct smox_thing **)objs;
+	struct smox_thing *old, *new;
+	struct smox_thing *thing;
+	unsigned long index;
+	void *entry;
+	int i;
+
+	for (i = 0; i < size; i++) {
+		old = ptrs[i];
+
+		new = kmem_cache_alloc(cachep, GFP_KERNEL);
+		if (!new) {
+			pr_debug("kmem_cache_alloc failed\n");
+			return;
+		}
+
+		new->id = old->id;
+
+		/* Update reference the brain dead way */
+		xa_for_each(&things, index, thing) {
+			if (thing == old) {
+				entry = xa_store(&things, index, new, GFP_KERNEL);
+				if (entry != old) {
+					pr_err("failed to exchange new/old\n");
+					return;
+				}
+			}
+		}
+		kmem_cache_free(cachep, old);
+	}
+}
+
+/*
+ * test_smo_xarray() - Run some tests using an XArray.
+ */
+static int test_smo_xarray(void)
+{
+	const int keep = 6; /* Free 5 out of 6 items */
+	const int nr_items = 10000;
+	struct smox_thing *thing;
+	unsigned long index;
+	void *entry;
+	int expected;
+	int i;
+
+	/*
+	 * Populate XArray, this adds to the radix_tree_node cache as
+	 * well as the smox_test cache.
+	 */
+	for (i = 0; i < nr_items; i++) {
+		thing = alloc_thing(i);
+		entry = xa_store(&things, i, thing, GFP_KERNEL);
+		if (xa_is_err(entry)) {
+			pr_err("smox: failed to allocate entry: %d\n", i);
+			return -ENOMEM;
+		}
+	}
+
+	/* Now free  items, putting holes in both caches. */
+	for (i = 0; i < nr_items; i++) {
+		if (i % keep == 0)
+			continue;
+
+		thing = xa_erase(&things, i);
+		if (xa_is_err(thing))
+			pr_err("smox: error erasing entry: %d\n", i);
+		kmem_cache_free(cachep, thing);
+	}
+
+	expected = 0;
+	xa_for_each(&things, index, thing) {
+		if (thing->id != expected || index != expected) {
+			pr_err("smox: error; got %ld want %d at %ld\n",
+			       thing->id, expected, index);
+			return -1;
+		}
+		expected += keep;
+	}
+
+	/*
+	 * Leave caches sparsely allocated.  Shrink caches manually with:
+	 *
+	 *   slabinfo radix_tree_node --shrink
+	 *   slabinfo smox_test --shrink
+	 */
+
+	return 0;
+}
+
+static int __init smox_cache_init(void)
+{
+	cachep = kmem_cache_create(SMOX_CACHE_NAME,
+				   sizeof(struct smox_thing),
+				   0, 0, smox_object_ctor);
+	if (!cachep)
+		return -1;
+
+	return 0;
+}
+
+static void __exit smox_cache_cleanup(void)
+{
+	struct smox_thing *thing;
+	unsigned long i;
+
+	xa_for_each(&things, i, thing) {
+		kmem_cache_free(cachep, thing);
+	}
+	xa_destroy(&things);
+	kmem_cache_destroy(cachep);
+}
+
+static int __init smox_init(void)
+{
+	int ret;
+
+	ret = smox_cache_init();
+	if (ret) {
+		pr_err("smo_xarray: failed to create cache\n");
+		return ret;
+	}
+	pr_info("smo_xarray: created kmem_cache: %s\n", SMOX_CACHE_NAME);
+
+	kmem_cache_setup_mobility(cachep, NULL, smox_cache_migrate);
+	pr_info("smo_xarray: kmem_cache %s defrag enabled\n", SMOX_CACHE_NAME);
+
+	/*
+	 * Running this test consumes memory unless you shrink the
+	 * radix_tree_node cache manually with `slabinfo`.
+	 */
+	ret = test_smo_xarray();
+	if (ret)
+		pr_warn("test_smo_xarray failed: %d\n", ret);
+
+	pr_info("smo_xarray: module loaded successfully\n");
+	return 0;
+}
+module_init(smox_init);
+
+static void __exit smox_exit(void)
+{
+	smox_cache_cleanup();
+
+	pr_info("smo_xarray: module removed\n");
+}
+module_exit(smox_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Tobin C. Harding");
+MODULE_DESCRIPTION("SMO XArray test module.");
-- 
2.21.0

[RFC PATCH v5 12/16] slub: Enable moving objects to/from specific nodes

[Tobin C. Harding]

We have just implemented Slab Movable Objects (object migration).
Currently object migration is used to defrag a cache.  On NUMA systems
it would be nice to be able to control the source and destination nodes
when moving objects.

Add CONFIG_SMO_NODE to guard this feature.  CONFIG_SMO_NODE depends on
CONFIG_SLUB_DEBUG because we use the full list.

Implement moving all objects (including those in full slabs) to a
specific node.  Expose this functionality to userspace via a sysfs entry.

Add sysfs entry:

   /sysfs/kernel/slab/<cache>/move

With this users get access to the following functionality:

 - Move all objects to specified node.

   	echo "N1" > move

 - Move all objects from specified node to other specified
   node (from N1 -> to N2):

   	echo "N1 N2" > move

This also enables shrinking slabs on a specific node:

   	echo "N1 N1" > move

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 mm/Kconfig |   7 ++
 mm/slub.c  | 249 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 256 insertions(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index ee8d1f311858..aa8d60e69a01 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -258,6 +258,13 @@ config ARCH_ENABLE_THP_MIGRATION
 config CONTIG_ALLOC
        def_bool (MEMORY_ISOLATION && COMPACTION) || CMA
 
+config SMO_NODE
+       bool "Enable per node control of Slab Movable Objects"
+       depends on SLUB && SYSFS
+       select SLUB_DEBUG
+       help
+         On NUMA systems enable moving objects to and from a specified node.
+
 config PHYS_ADDR_T_64BIT
 	def_bool 64BIT
 
diff --git a/mm/slub.c b/mm/slub.c
index 2157205df7ba..9582f2fc97d2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4336,6 +4336,106 @@ static void move_slab_page(struct page *page, void *scratch, int node)
 	s->migrate(s, vector, count, node, private);
 }
 
+#ifdef CONFIG_SMO_NODE
+/*
+ * kmem_cache_move() - Attempt to move all slab objects.
+ * @s: The cache we are working on.
+ * @node: The node to move objects away from.
+ * @target_node: The node to move objects on to.
+ *
+ * Attempts to move all objects (partial slabs and full slabs) to target
+ * node.
+ *
+ * Context: Takes the list_lock.
+ * Return: The number of slabs remaining on node.
+ */
+static unsigned long kmem_cache_move(struct kmem_cache *s,
+				     int node, int target_node)
+{
+	struct kmem_cache_node *n = get_node(s, node);
+	LIST_HEAD(move_list);
+	struct page *page, *page2;
+	unsigned long flags;
+	void **scratch;
+
+	if (!s->migrate) {
+		pr_warn("%s SMO not enabled, cannot move objects\n", s->name);
+		goto out;
+	}
+
+	scratch = alloc_scratch(s);
+	if (!scratch)
+		goto out;
+
+	spin_lock_irqsave(&n->list_lock, flags);
+
+	list_for_each_entry_safe(page, page2, &n->partial, lru) {
+		if (!slab_trylock(page))
+			/* Busy slab. Get out of the way */
+			continue;
+
+		if (page->inuse) {
+			list_move(&page->lru, &move_list);
+			/* Stop page being considered for allocations */
+			n->nr_partial--;
+			page->frozen = 1;
+
+			slab_unlock(page);
+		} else {	/* Empty slab page */
+			list_del(&page->lru);
+			n->nr_partial--;
+			slab_unlock(page);
+			discard_slab(s, page);
+		}
+	}
+	list_for_each_entry_safe(page, page2, &n->full, lru) {
+		if (!slab_trylock(page))
+			continue;
+
+		list_move(&page->lru, &move_list);
+		page->frozen = 1;
+		slab_unlock(page);
+	}
+
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	list_for_each_entry(page, &move_list, lru) {
+		if (page->inuse)
+			move_slab_page(page, scratch, target_node);
+	}
+	kfree(scratch);
+
+	/* Bail here to save taking the list_lock */
+	if (list_empty(&move_list))
+		goto out;
+
+	/* Inspect results and dispose of pages */
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry_safe(page, page2, &move_list, lru) {
+		list_del(&page->lru);
+		slab_lock(page);
+		page->frozen = 0;
+
+		if (page->inuse) {
+			if (page->inuse == page->objects) {
+				list_add(&page->lru, &n->full);
+				slab_unlock(page);
+			} else {
+				n->nr_partial++;
+				list_add_tail(&page->lru, &n->partial);
+				slab_unlock(page);
+			}
+		} else {
+			slab_unlock(page);
+			discard_slab(s, page);
+		}
+	}
+	spin_unlock_irqrestore(&n->list_lock, flags);
+out:
+	return atomic_long_read(&n->nr_slabs);
+}
+#endif	/* CONFIG_SMO_NODE */
+
 /*
  * kmem_cache_defrag() - Defragment node.
  * @s: cache we are working on.
@@ -4450,6 +4550,32 @@ static unsigned long kmem_cache_defrag(struct kmem_cache *s,
 	return n->nr_partial;
 }
 
+#ifdef CONFIG_SMO_NODE
+/*
+ * kmem_cache_move_to_node() - Move all slab objects to node.
+ * @s: The cache we are working on.
+ * @node: The target node to move objects to.
+ *
+ * Attempt to move all slab objects from all nodes to @node.
+ *
+ * Return: The total number of slabs left on emptied nodes.
+ */
+static unsigned long kmem_cache_move_to_node(struct kmem_cache *s, int node)
+{
+	unsigned long left = 0;
+	int nid;
+
+	for_each_node_state(nid, N_NORMAL_MEMORY) {
+		if (nid == node)
+			continue;
+
+		left += kmem_cache_move(s, nid, node);
+	}
+
+	return left;
+}
+#endif
+
 /**
  * kmem_defrag_slabs() - Defrag slab caches.
  * @node: The node to defrag or -1 for all nodes.
@@ -5594,6 +5720,126 @@ static ssize_t shrink_store(struct kmem_cache *s,
 }
 SLAB_ATTR(shrink);
 
+#ifdef CONFIG_SMO_NODE
+static ssize_t move_show(struct kmem_cache *s, char *buf)
+{
+	return 0;
+}
+
+/*
+ * parse_move_store_input() - Parse buf getting integer arguments.
+ * @buf: Buffer to parse.
+ * @length: Length of @buf.
+ * @arg0: Return parameter, first argument.
+ * @arg1: Return parameter, second argument.
+ *
+ * Parses the input from user write to sysfs file 'move'.  Input string
+ * should contain either one or two node specifiers of form Nx where x
+ * is an integer specifying the NUMA node ID.  'N' or 'n' may be used.
+ * n/N may be omitted.
+ *
+ * e.g.
+ *     echo 'N1' > /sysfs/kernel/slab/cache/move
+ * or
+ *     echo 'N0 N2' > /sysfs/kernel/slab/cache/move
+ *
+ * Regex matching accepted forms: '[nN]?[0-9]( [nN]?[0-9])?'
+ *
+ * FIXME: This is really fragile.  Input must be exactly correct,
+ *        spurious whitespace causes parse errors.
+ *
+ * Return: 0 if an argument was successfully converted, or an error code.
+ */
+static ssize_t parse_move_store_input(const char *buf, size_t length,
+				      long *arg0, long *arg1)
+{
+	char *s, *save, *ptr;
+	int ret = 0;
+
+	if (!buf)
+		return -EINVAL;
+
+	s = kstrdup(buf, GFP_KERNEL);
+	if (!s)
+		return -ENOMEM;
+	save = s;
+
+	if (s[length - 1] == '\n') {
+		s[length - 1] = '\0';
+		length--;
+	}
+
+	ptr = strsep(&s, " ");
+	if (!ptr || strcmp(ptr, "") == 0) {
+		ret = 0;
+		goto out;
+	}
+
+	if (*ptr == 'N' || *ptr == 'n')
+		ptr++;
+	ret = kstrtol(ptr, 10, arg0);
+	if (ret < 0)
+		goto out;
+
+	if (s) {
+		if (*s == 'N' || *s == 'n')
+			s++;
+		ret = kstrtol(s, 10, arg1);
+		if (ret < 0)
+			goto out;
+	}
+
+	ret = 0;
+out:
+	kfree(save);
+	return ret;
+}
+
+static bool is_valid_node(int node)
+{
+	int nid;
+
+	for_each_node_state(nid, N_NORMAL_MEMORY) {
+		if (nid == node)
+			return true;
+	}
+	return false;
+}
+
+/*
+ * move_store() - Move objects between nodes.
+ * @s: The cache we are working on.
+ * @buf: String received.
+ * @length: Length of @buf.
+ *
+ * Writes to /sys/kernel/slab/<cache>/move are interpreted as follows:
+ *
+ *  echo "N1" > move       : Move all objects (from all nodes) to node 1.
+ *  echo "N0 N1" > move    : Move all objects from node 0 to node 1.
+ *
+ * 'N' may be omitted:
+ */
+static ssize_t move_store(struct kmem_cache *s, const char *buf, size_t length)
+{
+	long arg0 = -1;
+	long arg1 = -1;
+	int ret;
+
+	ret = parse_move_store_input(buf, length, &arg0, &arg1);
+	if (ret < 0)
+		return -EINVAL;
+
+	if (is_valid_node(arg0) && is_valid_node(arg1))
+		(void)kmem_cache_move(s, arg0, arg1);
+	else if (is_valid_node(arg0))
+		(void)kmem_cache_move_to_node(s, arg0);
+
+	/* FIXME: What should we be returning here? */
+	return length;
+}
+SLAB_ATTR(move);
+#endif	/* CONFIG_SMO_NODE */
+
 #ifdef CONFIG_NUMA
 static ssize_t remote_node_defrag_ratio_show(struct kmem_cache *s, char *buf)
 {
@@ -5718,6 +5964,9 @@ static struct attribute *slab_attrs[] = {
 	&reclaim_account_attr.attr,
 	&destroy_by_rcu_attr.attr,
 	&shrink_attr.attr,
+#ifdef CONFIG_SMO_NODE
+	&move_attr.attr,
+#endif
 	&slabs_cpu_partial_attr.attr,
 #ifdef CONFIG_SLUB_DEBUG
 	&total_objects_attr.attr,
-- 
2.21.0

[RFC PATCH v5 13/16] slub: Enable balancing slabs across nodes

[Tobin C. Harding]

We have just implemented Slab Movable Objects (SMO).  On NUMA systems
slabs can become unbalanced i.e. many slabs on one node while other
nodes have few slabs.  Using SMO we can balance the slabs across all
the nodes.

The algorithm used is as follows:

 1. Move all objects to node 0 (this has the effect of defragmenting the
    cache).

 2. Calculate the desired number of slabs for each node (this is done
    using the approximation nr_slabs / nr_nodes).

 3. Loop over the nodes moving the desired number of slabs from node 0
    to the node.

Feature is conditionally built in with CONFIG_SMO_NODE, this is because
we need the full list (we enable SLUB_DEBUG to get this).  Future
version may separate final list out of SLUB_DEBUG.

Expose this functionality to userspace via a sysfs entry.  Add sysfs
entry:

       /sysfs/kernel/slab/<cache>/balance

Write of '1' to this file triggers balance, no other value accepted.

This feature relies on SMO being enable for the cache, this is done with
a call to, after the isolate/migrate functions have been defined.

	kmem_cache_setup_mobility(s, isolate, migrate)

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 mm/slub.c | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index 9582f2fc97d2..25b6d1e408e3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4574,6 +4574,109 @@ static unsigned long kmem_cache_move_to_node(struct kmem_cache *s, int node)
 
 	return left;
 }
+
+/*
+ * kmem_cache_move_slabs() - Attempt to move @num slabs to target_node,
+ * @s: The cache we are working on.
+ * @node: The node to move objects from.
+ * @target_node: The node to move objects to.
+ * @num: The number of slabs to move.
+ *
+ * Attempts to move @num slabs from @node to @target_node.  This is done
+ * by migrating objects from slabs on the full_list.
+ *
+ * Return: The number of slabs moved or error code.
+ */
+static long kmem_cache_move_slabs(struct kmem_cache *s,
+				  int node, int target_node, long num)
+{
+	struct kmem_cache_node *n = get_node(s, node);
+	LIST_HEAD(move_list);
+	struct page *page, *page2;
+	unsigned long flags;
+	void **scratch;
+	long done = 0;
+
+	if (node == target_node)
+		return -EINVAL;
+
+	scratch = alloc_scratch(s);
+	if (!scratch)
+		return -ENOMEM;
+
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry_safe(page, page2, &n->full, lru) {
+		if (!slab_trylock(page))
+			/* Busy slab. Get out of the way */
+			continue;
+
+		list_move(&page->lru, &move_list);
+		page->frozen = 1;
+		slab_unlock(page);
+
+		if (++done >= num)
+			break;
+	}
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	list_for_each_entry(page, &move_list, lru) {
+		if (page->inuse)
+			move_slab_page(page, scratch, target_node);
+	}
+	kfree(scratch);
+
+	/* Inspect results and dispose of pages */
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry_safe(page, page2, &move_list, lru) {
+		list_del(&page->lru);
+		slab_lock(page);
+		page->frozen = 0;
+
+		if (page->inuse) {
+			/*
+			 * This is best effort only, if slab still has
+			 * objects just put it back on the partial list.
+			 */
+			n->nr_partial++;
+			list_add_tail(&page->lru, &n->partial);
+			slab_unlock(page);
+		} else {
+			slab_unlock(page);
+			discard_slab(s, page);
+		}
+	}
+	spin_unlock_irqrestore(&n->list_lock, flags);
+
+	return done;
+}
+
+/*
+ * kmem_cache_balance_nodes() - Balance slabs across nodes.
+ * @s: The cache we are working on.
+ */
+static void kmem_cache_balance_nodes(struct kmem_cache *s)
+{
+	struct kmem_cache_node *n = get_node(s, 0);
+	unsigned long desired_nr_slabs_per_node;
+	unsigned long nr_slabs;
+	int nr_nodes = 0;
+	int nid;
+
+	(void)kmem_cache_move_to_node(s, 0);
+
+	for_each_node_state(nid, N_NORMAL_MEMORY)
+		nr_nodes++;
+
+	nr_slabs = atomic_long_read(&n->nr_slabs);
+	desired_nr_slabs_per_node = nr_slabs / nr_nodes;
+
+	for_each_node_state(nid, N_NORMAL_MEMORY) {
+		if (nid == 0)
+			continue;
+
+		kmem_cache_move_slabs(s, 0, nid, desired_nr_slabs_per_node);
+	}
+}
 #endif
 
 /**
@@ -5838,6 +5941,22 @@ static ssize_t move_store(struct kmem_cache *s, const char *buf, size_t length)
 	return length;
 }
 SLAB_ATTR(move);
+
+static ssize_t balance_show(struct kmem_cache *s, char *buf)
+{
+	return 0;
+}
+
+static ssize_t balance_store(struct kmem_cache *s,
+			     const char *buf, size_t length)
+{
+	if (buf[0] == '1')
+		kmem_cache_balance_nodes(s);
+	else
+		return -EINVAL;
+	return length;
+}
+SLAB_ATTR(balance);
 #endif	/* CONFIG_SMO_NODE */
 
 #ifdef CONFIG_NUMA
@@ -5966,6 +6085,7 @@ static struct attribute *slab_attrs[] = {
 	&shrink_attr.attr,
 #ifdef CONFIG_SMO_NODE
 	&move_attr.attr,
+	&balance_attr.attr,
 #endif
 	&slabs_cpu_partial_attr.attr,
 #ifdef CONFIG_SLUB_DEBUG
-- 
2.21.0

[RFC PATCH v5 14/16] dcache: Provide a dentry constructor

[Tobin C. Harding]

In order to support object migration on the dentry cache we need to have
a determined object state at all times. Without a constructor the object
would have a random state after allocation.

Provide a dentry constructor.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 fs/dcache.c | 30 +++++++++++++++++++++---------
 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 8136bda27a1f..b7318615979d 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1602,6 +1602,16 @@ void d_invalidate(struct dentry *dentry)
 }
 EXPORT_SYMBOL(d_invalidate);
 
+static void dcache_ctor(void *p)
+{
+	struct dentry *dentry = p;
+
+	/* Mimic lockref_mark_dead() */
+	dentry->d_lockref.count = -128;
+
+	spin_lock_init(&dentry->d_lock);
+}
+
 /**
  * __d_alloc	-	allocate a dcache entry
  * @sb: filesystem it will belong to
@@ -1657,7 +1667,6 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 
 	dentry->d_lockref.count = 1;
 	dentry->d_flags = 0;
-	spin_lock_init(&dentry->d_lock);
 	seqcount_init(&dentry->d_seq);
 	dentry->d_inode = NULL;
 	dentry->d_parent = dentry;
@@ -3095,14 +3104,17 @@ static void __init dcache_init_early(void)
 
 static void __init dcache_init(void)
 {
-	/*
-	 * A constructor could be added for stable state like the lists,
-	 * but it is probably not worth it because of the cache nature
-	 * of the dcache.
-	 */
-	dentry_cache = KMEM_CACHE_USERCOPY(dentry,
-		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
-		d_iname);
+	slab_flags_t flags =
+		SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | SLAB_MEM_SPREAD | SLAB_ACCOUNT;
+
+	dentry_cache =
+		kmem_cache_create_usercopy("dentry",
+					   sizeof(struct dentry),
+					   __alignof__(struct dentry),
+					   flags,
+					   offsetof(struct dentry, d_iname),
+					   sizeof_field(struct dentry, d_iname),
+					   dcache_ctor);
 
 	/* Hash may have been set up in dcache_init_early */
 	if (!hashdist)
-- 
2.21.0

[RFC PATCH v5 15/16] dcache: Implement partial shrink via Slab Movable Objects

[Tobin C. Harding]

The dentry slab cache is susceptible to internal fragmentation.  Now
that we have Slab Movable Objects we can attempt to defragment the
dcache.  Dentry objects are inherently _not_ relocatable however under
some conditions they can be free'd.  This is the same as shrinking the
dcache but instead of shrinking the whole cache we only attempt to free
those objects that are located in partially full slab pages.  There is
no guarantee that this will reduce the memory usage of the system, it is
a compromise between fragmented memory and total cache shrinkage with
the hope that some memory pressure can be alleviated.

This is implemented using the newly added Slab Movable Objects
infrastructure.  The dcache 'migration' function is intentionally _not_
called 'd_migrate' because we only free, we do not migrate.  Call it
'd_partial_shrink' to make explicit that no reallocation is done.

Implement isolate and 'migrate' functions for the dentry slab cache.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
 fs/dcache.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index b7318615979d..0dfe580c2d42 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -31,6 +31,7 @@
 #include <linux/bit_spinlock.h>
 #include <linux/rculist_bl.h>
 #include <linux/list_lru.h>
+#include <linux/backing-dev.h>
 #include "internal.h"
 #include "mount.h"
 
@@ -3071,6 +3072,79 @@ void d_tmpfile(struct dentry *dentry, struct inode *inode)
 }
 EXPORT_SYMBOL(d_tmpfile);
 
+/*
+ * d_isolate() - Dentry isolation callback function.
+ * @s: The dentry cache.
+ * @v: Vector of pointers to the objects to isolate.
+ * @nr: Number of objects in @v.
+ *
+ * The slab allocator is holding off frees. We can safely examine
+ * the object without the danger of it vanishing from under us.
+ */
+static void *d_isolate(struct kmem_cache *s, void **v, int nr)
+{
+	struct list_head *dispose;
+	struct dentry *dentry;
+	int i;
+
+	dispose = kmalloc(sizeof(*dispose), GFP_KERNEL);
+	if (!dispose)
+		return NULL;
+
+	INIT_LIST_HEAD(dispose);
+
+	for (i = 0; i < nr; i++) {
+		dentry = v[i];
+		spin_lock(&dentry->d_lock);
+
+		if (dentry->d_lockref.count > 0 ||
+		    dentry->d_flags & DCACHE_SHRINK_LIST) {
+			spin_unlock(&dentry->d_lock);
+			continue;
+		}
+
+		if (dentry->d_flags & DCACHE_LRU_LIST)
+			d_lru_del(dentry);
+
+		d_shrink_add(dentry, dispose);
+		spin_unlock(&dentry->d_lock);
+	}
+
+	return dispose;
+}
+
+/*
+ * d_partial_shrink() - Dentry migration callback function.
+ * @s: The dentry cache.
+ * @_unused: We do not access the vector.
+ * @__unused: No need for length of vector.
+ * @___unused: We do not do any allocation.
+ * @private: list_head pointer representing the shrink list.
+ *
+ * Dispose of the shrink list created during isolation function.
+ *
+ * Dentry objects can _not_ be relocated and shrinking the whole dcache
+ * can be expensive.  This is an effort to free dentry objects that are
+ * stopping slab pages from being free'd without clearing the whole dcache.
+ *
+ * This callback is called from the SLUB allocator object migration
+ * infrastructure in attempt to free up slab pages by freeing dentry
+ * objects from partially full slabs.
+ */
+static void d_partial_shrink(struct kmem_cache *s, void **_unused, int __unused,
+			     int ___unused, void *private)
+{
+	struct list_head *dispose = private;
+
+	if (!private)		/* kmalloc error during isolate. */
+		return;
+
+	if (!list_empty(dispose))
+		shrink_dentry_list(dispose);
+
+	kfree(private);
+}
+
 static __initdata unsigned long dhash_entries;
 static int __init set_dhash_entries(char *str)
 {
@@ -3116,6 +3190,8 @@ static void __init dcache_init(void)
 					   sizeof_field(struct dentry, d_iname),
 					   dcache_ctor);
 
+	kmem_cache_setup_mobility(dentry_cache, d_isolate, d_partial_shrink);
+
 	/* Hash may have been set up in dcache_init_early */
 	if (!hashdist)
 		return;
-- 
2.21.0

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

[Tobin C. Harding]

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

Re: [RFC PATCH v5 01/16] slub: Add isolate() and migrate() methods

[Roman Gushchin]

On Mon, May 20, 2019 at 03:40:02PM +1000, Tobin C. Harding wrote:
> Add the two methods needed for moving objects and enable the display of
> the callbacks via the /sys/kernel/slab interface.
> 
> Add documentation explaining the use of these methods and the prototypes
> for slab.h. Add functions to setup the callbacks method for a slab
> cache.
> 
> Add empty functions for SLAB/SLOB. The API is generic so it could be
> theoretically implemented for these allocators as well.
> 
> Change sysfs 'ctor' field to be 'ops' to contain all the callback
> operations defined for a slab cache.  Display the existing 'ctor'
> callback in the ops fields contents along with 'isolate' and 'migrate'
> callbacks.
> 
> Co-developed-by: Christoph Lameter <cl@linux.com>
> Signed-off-by: Tobin C. Harding <tobin@kernel.org>
> ---
>  include/linux/slab.h     | 70 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/slub_def.h |  3 ++
>  mm/slub.c                | 59 +++++++++++++++++++++++++++++----
>  3 files changed, 126 insertions(+), 6 deletions(-)

Reviewed-by: Roman Gushchin <guro@fb.com>

Thanks!

Re: [RFC PATCH v5 03/16] slub: Sort slab cache list

[Roman Gushchin]

On Mon, May 20, 2019 at 03:40:04PM +1000, Tobin C. Harding wrote:
> It is advantageous to have all defragmentable slabs together at the
> beginning of the list of slabs so that there is no need to scan the
> complete list. Put defragmentable caches first when adding a slab cache
> and others last.
> 
> Co-developed-by: Christoph Lameter <cl@linux.com>
> Signed-off-by: Tobin C. Harding <tobin@kernel.org>

Reviewed-by: Roman Gushchin <guro@fb.com>

Re: [RFC PATCH v5 04/16] slub: Slab defrag core

[Roman Gushchin]

On Mon, May 20, 2019 at 03:40:05PM +1000, Tobin C. Harding wrote:
> Internal fragmentation can occur within pages used by the slub
> allocator.  Under some workloads large numbers of pages can be used by
> partial slab pages.  This under-utilisation is bad simply because it
> wastes memory but also because if the system is under memory pressure
> higher order allocations may become difficult to satisfy.  If we can
> defrag slab caches we can alleviate these problems.
> 
> Implement Slab Movable Objects in order to defragment slab caches.
> 
> Slab defragmentation may occur:
> 
> 1. Unconditionally when __kmem_cache_shrink() is called on a slab cache
>    by the kernel calling kmem_cache_shrink().
> 
> 2. Unconditionally through the use of the slabinfo command.
> 
> 	slabinfo <cache> -s
> 
> 3. Conditionally via the use of kmem_cache_defrag()
> 
> - Use Slab Movable Objects when shrinking cache.
> 
> Currently when the kernel calls kmem_cache_shrink() we curate the
> partial slabs list.  If object migration is not enabled for the cache we
> still do this, if however, SMO is enabled we attempt to move objects in
> partially full slabs in order to defragment the cache.  Shrink attempts
> to move all objects in order to reduce the cache to a single partial
> slab for each node.
> 
> - Add conditional per node defrag via new function:
> 
> 	kmem_defrag_slabs(int node).
> 
> kmem_defrag_slabs() attempts to defragment all slab caches for
> node. Defragmentation is done conditionally dependent on MAX_PARTIAL
> _and_ defrag_used_ratio.
> 
>    Caches are only considered for defragmentation if the number of
>    partial slabs exceeds MAX_PARTIAL (per node).
> 
>    Also, defragmentation only occurs if the usage ratio of the slab is
>    lower than the configured percentage (sysfs field added in this
>    patch).  Fragmentation ratios are measured by calculating the
>    percentage of objects in use compared to the total number of objects
>    that the slab page can accommodate.
> 
>    The scanning of slab caches is optimized because the defragmentable
>    slabs come first on the list. Thus we can terminate scans on the
>    first slab encountered that does not support defragmentation.
> 
>    kmem_defrag_slabs() takes a node parameter. This can either be -1 if
>    defragmentation should be performed on all nodes, or a node number.
> 
>    Defragmentation may be disabled by setting defrag ratio to 0
> 
> 	echo 0 > /sys/kernel/slab/<cache>/defrag_used_ratio
> 
> - Add a defrag ratio sysfs field and set it to 30% by default. A limit
> of 30% specifies that more than 3 out of 10 available slots for objects
> need to be in use otherwise slab defragmentation will be attempted on
> the remaining objects.
> 
> In order for a cache to be defragmentable the cache must support object
> migration (SMO).  Enabling SMO for a cache is done via a call to the
> recently added function:
> 
> 	void kmem_cache_setup_mobility(struct kmem_cache *,
> 				       kmem_cache_isolate_func,
> 			               kmem_cache_migrate_func);
> 
> Co-developed-by: Christoph Lameter <cl@linux.com>
> Signed-off-by: Tobin C. Harding <tobin@kernel.org>
> ---
>  Documentation/ABI/testing/sysfs-kernel-slab |  14 +
>  include/linux/slab.h                        |   1 +
>  include/linux/slub_def.h                    |   7 +
>  mm/slub.c                                   | 385 ++++++++++++++++----
>  4 files changed, 334 insertions(+), 73 deletions(-)

Hi Tobin!

Overall looks very good to me! I'll take another look when you'll post
a non-RFC version, but so far I can't find any issues.

A generic question: as I understand, you do support only root kmemcaches now.
Is kmemcg support in plans?

Without it the patchset isn't as attractive to anyone using cgroups,
as it could be. Also, I hope it can solve (or mitigate) the memcg-specific
problem of scattering vfs cache workingset over multiple generations of the
same cgroup (their kmem_caches).

Thanks!

> 
> diff --git a/Documentation/ABI/testing/sysfs-kernel-slab b/Documentation/ABI/testing/sysfs-kernel-slab
> index 29601d93a1c2..c6f129af035a 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-slab
> +++ b/Documentation/ABI/testing/sysfs-kernel-slab
> @@ -180,6 +180,20 @@ Description:
>  		list.  It can be written to clear the current count.
>  		Available when CONFIG_SLUB_STATS is enabled.
>  
> +What:		/sys/kernel/slab/cache/defrag_used_ratio
> +Date:		May 2019
> +KernelVersion:	5.2
> +Contact:	Christoph Lameter <cl@linux-foundation.org>
> +		Pekka Enberg <penberg@cs.helsinki.fi>,
> +Description:
> +		The defrag_used_ratio file allows the control of how aggressive
> +		slab fragmentation reduction works at reclaiming objects from
> +		sparsely populated slabs. This is a percentage. If a slab has
> +		less than this percentage of objects allocated then reclaim will
> +		attempt to reclaim objects so that the whole slab page can be
> +		freed. 0% specifies no reclaim attempt (defrag disabled), 100%
> +		specifies attempt to reclaim all pages.  The default is 30%.
> +
>  What:		/sys/kernel/slab/cache/deactivate_to_tail
>  Date:		February 2008
>  KernelVersion:	2.6.25
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 886fc130334d..4bf381b34829 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -149,6 +149,7 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name,
>  			void (*ctor)(void *));
>  void kmem_cache_destroy(struct kmem_cache *);
>  int kmem_cache_shrink(struct kmem_cache *);
> +unsigned long kmem_defrag_slabs(int node);
>  
>  void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
>  void memcg_deactivate_kmem_caches(struct mem_cgroup *);
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index 2879a2f5f8eb..34c6f1250652 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -107,6 +107,13 @@ struct kmem_cache {
>  	unsigned int red_left_pad;	/* Left redzone padding size */
>  	const char *name;	/* Name (only for display!) */
>  	struct list_head list;	/* List of slab caches */
> +	int defrag_used_ratio;	/*
> +				 * Ratio used to check against the
> +				 * percentage of objects allocated in a
> +				 * slab page.  If less than this ratio
> +				 * is allocated then reclaim attempts
> +				 * are made.
> +				 */
>  #ifdef CONFIG_SYSFS
>  	struct kobject kobj;	/* For sysfs */
>  	struct work_struct kobj_remove_work;
> diff --git a/mm/slub.c b/mm/slub.c
> index 66d474397c0f..2157205df7ba 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -355,6 +355,12 @@ static __always_inline void slab_lock(struct page *page)
>  	bit_spin_lock(PG_locked, &page->flags);
>  }
>  
> +static __always_inline int slab_trylock(struct page *page)
> +{
> +	VM_BUG_ON_PAGE(PageTail(page), page);
> +	return bit_spin_trylock(PG_locked, &page->flags);
> +}
> +
>  static __always_inline void slab_unlock(struct page *page)
>  {
>  	VM_BUG_ON_PAGE(PageTail(page), page);
> @@ -3634,6 +3640,7 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
>  
>  	set_cpu_partial(s);
>  
> +	s->defrag_used_ratio = 30;
>  #ifdef CONFIG_NUMA
>  	s->remote_node_defrag_ratio = 1000;
>  #endif
> @@ -3950,79 +3957,6 @@ void kfree(const void *x)
>  }
>  EXPORT_SYMBOL(kfree);
>  
> -#define SHRINK_PROMOTE_MAX 32
> -
> -/*
> - * kmem_cache_shrink discards empty slabs and promotes the slabs filled
> - * up most to the head of the partial lists. New allocations will then
> - * fill those up and thus they can be removed from the partial lists.
> - *
> - * The slabs with the least items are placed last. This results in them
> - * being allocated from last increasing the chance that the last objects
> - * are freed in them.
> - */
> -int __kmem_cache_shrink(struct kmem_cache *s)
> -{
> -	int node;
> -	int i;
> -	struct kmem_cache_node *n;
> -	struct page *page;
> -	struct page *t;
> -	struct list_head discard;
> -	struct list_head promote[SHRINK_PROMOTE_MAX];
> -	unsigned long flags;
> -	int ret = 0;
> -
> -	flush_all(s);
> -	for_each_kmem_cache_node(s, node, n) {
> -		INIT_LIST_HEAD(&discard);
> -		for (i = 0; i < SHRINK_PROMOTE_MAX; i++)
> -			INIT_LIST_HEAD(promote + i);
> -
> -		spin_lock_irqsave(&n->list_lock, flags);
> -
> -		/*
> -		 * Build lists of slabs to discard or promote.
> -		 *
> -		 * Note that concurrent frees may occur while we hold the
> -		 * list_lock. page->inuse here is the upper limit.
> -		 */
> -		list_for_each_entry_safe(page, t, &n->partial, slab_list) {
> -			int free = page->objects - page->inuse;
> -
> -			/* Do not reread page->inuse */
> -			barrier();
> -
> -			/* We do not keep full slabs on the list */
> -			BUG_ON(free <= 0);
> -
> -			if (free == page->objects) {
> -				list_move(&page->slab_list, &discard);
> -				n->nr_partial--;
> -			} else if (free <= SHRINK_PROMOTE_MAX)
> -				list_move(&page->slab_list, promote + free - 1);
> -		}
> -
> -		/*
> -		 * Promote the slabs filled up most to the head of the
> -		 * partial list.
> -		 */
> -		for (i = SHRINK_PROMOTE_MAX - 1; i >= 0; i--)
> -			list_splice(promote + i, &n->partial);
> -
> -		spin_unlock_irqrestore(&n->list_lock, flags);
> -
> -		/* Release empty slabs */
> -		list_for_each_entry_safe(page, t, &discard, slab_list)
> -			discard_slab(s, page);
> -
> -		if (slabs_node(s, node))
> -			ret = 1;
> -	}
> -
> -	return ret;
> -}
> -
>  #ifdef CONFIG_MEMCG
>  static void kmemcg_cache_deact_after_rcu(struct kmem_cache *s)
>  {
> @@ -4317,6 +4251,287 @@ int __kmem_cache_create(struct kmem_cache *s, slab_flags_t flags)
>  	return err;
>  }
>  
> +/*
> + * Allocate a slab scratch space that is sufficient to keep pointers to
> + * individual objects for all objects in cache and also a bitmap for the
> + * objects (used to mark which objects are active).
> + */
> +static inline void *alloc_scratch(struct kmem_cache *s)
> +{
> +	unsigned int size = oo_objects(s->max);
> +
> +	return kmalloc(size * sizeof(void *) +
> +		       BITS_TO_LONGS(size) * sizeof(unsigned long),
> +		       GFP_KERNEL);
> +}

I'd pass a single number (s->max) instead of s here.

> +
> +/*
> + * move_slab_page() - Move all objects in the given slab.
> + * @page: The slab we are working on.
> + * @scratch: Pointer to scratch space.
> + * @node: The target node to move objects to.
> + *
> + * If the target node is not the current node then the object is moved
> + * to the target node.  If the target node is the current node then this
> + * is an effective way of defragmentation since the current slab page
> + * with its object is exempt from allocation.
> + */
> +static void move_slab_page(struct page *page, void *scratch, int node)
> +{
> +	unsigned long objects;
> +	struct kmem_cache *s;
> +	unsigned long flags;
> +	unsigned long *map;
> +	void *private;
> +	int count;
> +	void *p;
> +	void **vector = scratch;
> +	void *addr = page_address(page);
> +
> +	local_irq_save(flags);
> +	slab_lock(page);
> +
> +	BUG_ON(!PageSlab(page)); /* Must be a slab page */
> +	BUG_ON(!page->frozen);	 /* Slab must have been frozen earlier */
> +
> +	s = page->slab_cache;
> +	objects = page->objects;
> +	map = scratch + objects * sizeof(void **);
> +
> +	/* Determine used objects */
> +	bitmap_fill(map, objects);
> +	for (p = page->freelist; p; p = get_freepointer(s, p))
> +		__clear_bit(slab_index(p, s, addr), map);
> +
> +	/* Build vector of pointers to objects */
> +	count = 0;
> +	memset(vector, 0, objects * sizeof(void **));
> +	for_each_object(p, s, addr, objects)
> +		if (test_bit(slab_index(p, s, addr), map))
> +			vector[count++] = p;
> +
> +	if (s->isolate)
> +		private = s->isolate(s, vector, count);
> +	else
> +		/* Objects do not need to be isolated */
> +		private = NULL;
> +
> +	/*
> +	 * Pinned the objects. Now we can drop the slab lock. The slab
> +	 * is frozen so it cannot vanish from under us nor will
> +	 * allocations be performed on the slab. However, unlocking the
> +	 * slab will allow concurrent slab_frees to proceed. So the
> +	 * subsystem must have a way to tell from the content of the
> +	 * object that it was freed.
> +	 *
> +	 * If neither RCU nor ctor is being used then the object may be
> +	 * modified by the allocator after being freed which may disrupt
> +	 * the ability of the migrate function to tell if the object is
> +	 * free or not.
> +	 */
> +	slab_unlock(page);
> +	local_irq_restore(flags);
> +
> +	/* Perform callback to move the objects */
> +	s->migrate(s, vector, count, node, private);
> +}
> +
> +/*
> + * kmem_cache_defrag() - Defragment node.
> + * @s: cache we are working on.
> + * @node: The node to move objects from.
> + * @target_node: The node to move objects to.
> + * @ratio: The defrag ratio (percentage, between 0 and 100).
> + *
> + * Release slabs with zero objects and try to call the migration function
> + * for slabs with less than the 'ratio' percentage of objects allocated.
> + *
> + * Moved objects are allocated on @target_node.
> + *
> + * Return: The number of partial slabs left on @node after the
> + *         operation.
> + */
> +static unsigned long kmem_cache_defrag(struct kmem_cache *s,
> +				       int node, int target_node, int ratio)
> +{
> +	struct kmem_cache_node *n = get_node(s, node);
> +	struct page *page, *page2;
> +	LIST_HEAD(move_list);
> +	unsigned long flags;
> +
> +	if (node == target_node && n->nr_partial <= 1) {
> +		/*
> +		 * Trying to reduce fragmentation on a node but there is
> +		 * only a single or no partial slab page. This is already
> +		 * the optimal object density that we can reach.
> +		 */
> +		return n->nr_partial;
> +	}
> +
> +	spin_lock_irqsave(&n->list_lock, flags);
> +	list_for_each_entry_safe(page, page2, &n->partial, lru) {
> +		if (!slab_trylock(page))
> +			/* Busy slab. Get out of the way */
> +			continue;
> +
> +		if (page->inuse) {
> +			if (page->inuse > ratio * page->objects / 100) {
> +				slab_unlock(page);
> +				/*
> +				 * Skip slab because the object density
> +				 * in the slab page is high enough.
> +				 */
> +				continue;
> +			}
> +
> +			list_move(&page->lru, &move_list);
> +			if (s->migrate) {
> +				/* Stop page being considered for allocations */
> +				n->nr_partial--;
> +				page->frozen = 1;
> +			}
> +			slab_unlock(page);
> +		} else {	/* Empty slab page */
> +			list_del(&page->lru);
> +			n->nr_partial--;
> +			slab_unlock(page);
> +			discard_slab(s, page);
> +		}
> +	}
> +
> +	if (!s->migrate) {
> +		/*
> +		 * No defrag method. By simply putting the zaplist at
> +		 * the end of the partial list we can let them simmer
> +		 * longer and thus increase the chance of all objects
> +		 * being reclaimed.
> +		 */
> +		list_splice(&move_list, n->partial.prev);
> +	}
> +
> +	spin_unlock_irqrestore(&n->list_lock, flags);
> +
> +	if (s->migrate && !list_empty(&move_list)) {
> +		void **scratch = alloc_scratch(s);
> +		if (scratch) {
> +			/* Try to remove / move the objects left */
> +			list_for_each_entry(page, &move_list, lru) {
> +				if (page->inuse)
> +					move_slab_page(page, scratch, target_node);
> +			}
> +			kfree(scratch);
> +		}
> +
> +		/* Inspect results and dispose of pages */
> +		spin_lock_irqsave(&n->list_lock, flags);
> +		list_for_each_entry_safe(page, page2, &move_list, lru) {
> +			list_del(&page->lru);
> +			slab_lock(page);
> +			page->frozen = 0;
> +
> +			if (page->inuse) {
> +				/*
> +				 * Objects left in slab page, move it to the
> +				 * tail of the partial list to increase the
> +				 * chance that the freeing of the remaining
> +				 * objects will free the slab page.
> +				 */
> +				n->nr_partial++;
> +				list_add_tail(&page->lru, &n->partial);
> +				slab_unlock(page);
> +			} else {
> +				slab_unlock(page);
> +				discard_slab(s, page);
> +			}
> +		}
> +		spin_unlock_irqrestore(&n->list_lock, flags);
> +	}
> +
> +	return n->nr_partial;
> +}
> +
> +/**
> + * kmem_defrag_slabs() - Defrag slab caches.
> + * @node: The node to defrag or -1 for all nodes.
> + *
> + * Defrag slabs conditional on the amount of fragmentation in a page.
> + *
> + * Return: The total number of partial slabs in migratable caches left
> + *         on @node after the operation.
> + */
> +unsigned long kmem_defrag_slabs(int node)
> +{
> +	struct kmem_cache *s;
> +	unsigned long left = 0;
> +	int nid;
> +
> +	if (node >= MAX_NUMNODES)
> +		return -EINVAL;
> +
> +	/*
> +	 * kmem_defrag_slabs() may be called from the reclaim path which
> +	 * may be called for any page allocator alloc. So there is the
> +	 * danger that we get called in a situation where slub already
> +	 * acquired the slub_lock for other purposes.
> +	 */
> +	if (!mutex_trylock(&slab_mutex))
> +		return 0;
> +
> +	list_for_each_entry(s, &slab_caches, list) {
> +		/*
> +		 * Defragmentable caches come first. If the slab cache is
> +		 * not defragmentable then we can stop traversing the list.
> +		 */
> +		if (!s->migrate)
> +			break;
> +
> +		if (node >= 0) {
> +			if (s->node[node]->nr_partial > MAX_PARTIAL) {
> +				left += kmem_cache_defrag(s, node, node,
> +							  s->defrag_used_ratio);
> +			}
> +			continue;
> +		}
> +
> +		for_each_node_state(nid, N_NORMAL_MEMORY) {
> +			if (s->node[nid]->nr_partial > MAX_PARTIAL) {
> +				left += kmem_cache_defrag(s, nid, nid,
> +							  s->defrag_used_ratio);
> +			}
> +		}
> +	}
> +	mutex_unlock(&slab_mutex);
> +	return left;
> +}
> +EXPORT_SYMBOL(kmem_defrag_slabs);
> +
> +/**
> + * __kmem_cache_shrink() - Shrink a cache.
> + * @s: The cache to shrink.
> + *
> + * Reduces the memory footprint of a slab cache by as much as possible.
> + *
> + * This works by:
> + *  1. Removing empty slabs from the partial list.
> + *  2. Migrating slab objects to denser slab pages if the slab cache
> + *  supports migration.  If not, reorganizing the partial list so that
> + *  more densely allocated slab pages come first.
> + *
> + * Not called directly, called by kmem_cache_shrink().
> + */
> +int __kmem_cache_shrink(struct kmem_cache *s)
> +{
> +	int node;
> +	int left = 0;
> +
> +	flush_all(s);
> +	for_each_node_state(node, N_NORMAL_MEMORY)
> +		left += kmem_cache_defrag(s, node, node, 100);
> +
> +	return left;
> +}
> +EXPORT_SYMBOL(__kmem_cache_shrink);
> +
>  void kmem_cache_setup_mobility(struct kmem_cache *s,
>  			       kmem_cache_isolate_func isolate,
>  			       kmem_cache_migrate_func migrate)
> @@ -5168,6 +5383,29 @@ static ssize_t destroy_by_rcu_show(struct kmem_cache *s, char *buf)
>  }
>  SLAB_ATTR_RO(destroy_by_rcu);
>  
> +static ssize_t defrag_used_ratio_show(struct kmem_cache *s, char *buf)
> +{
> +	return sprintf(buf, "%d\n", s->defrag_used_ratio);
> +}
> +
> +static ssize_t defrag_used_ratio_store(struct kmem_cache *s,
> +				       const char *buf, size_t length)
> +{
> +	unsigned long ratio;
> +	int err;
> +
> +	err = kstrtoul(buf, 10, &ratio);
> +	if (err)
> +		return err;
> +
> +	if (ratio > 100)
> +		return -EINVAL;
> +
> +	s->defrag_used_ratio = ratio;
> +	return length;
> +}
> +SLAB_ATTR(defrag_used_ratio);
> +
>  #ifdef CONFIG_SLUB_DEBUG
>  static ssize_t slabs_show(struct kmem_cache *s, char *buf)
>  {
> @@ -5492,6 +5730,7 @@ static struct attribute *slab_attrs[] = {
>  	&validate_attr.attr,
>  	&alloc_calls_attr.attr,
>  	&free_calls_attr.attr,
> +	&defrag_used_ratio_attr.attr,
>  #endif
>  #ifdef CONFIG_ZONE_DMA
>  	&cache_dma_attr.attr,
> -- 
> 2.21.0
> 

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

[Roman Gushchin]

On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> 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.

Hm, isn't it better to make it a static branch? Or basically anything
that allows switching on the fly?

It seems that the cost of just building it in shouldn't be that high.
And the question if the defragmentation worth the trouble is so much
easier to answer if it's possible to turn it on and off without rebooting.

Thanks!

> 
> 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
> 

Re: [RFC PATCH v5 13/16] slub: Enable balancing slabs across nodes

[Roman Gushchin]

On Mon, May 20, 2019 at 03:40:14PM +1000, Tobin C. Harding wrote:
> We have just implemented Slab Movable Objects (SMO).  On NUMA systems
> slabs can become unbalanced i.e. many slabs on one node while other
> nodes have few slabs.  Using SMO we can balance the slabs across all
> the nodes.
> 
> The algorithm used is as follows:
> 
>  1. Move all objects to node 0 (this has the effect of defragmenting the
>     cache).

This already sounds dangerous (or costly). Can't it be done without
cross-node data moves?

> 
>  2. Calculate the desired number of slabs for each node (this is done
>     using the approximation nr_slabs / nr_nodes).

So that on this step only (actual data size - desired data size) has
to be moved?

Thanks!

Re: [RFC PATCH v5 04/16] slub: Slab defrag core

[Tobin C. Harding]

On Tue, May 21, 2019 at 12:51:57AM +0000, Roman Gushchin wrote:
> On Mon, May 20, 2019 at 03:40:05PM +1000, Tobin C. Harding wrote:
> > Internal fragmentation can occur within pages used by the slub
> > allocator.  Under some workloads large numbers of pages can be used by
> > partial slab pages.  This under-utilisation is bad simply because it
> > wastes memory but also because if the system is under memory pressure
> > higher order allocations may become difficult to satisfy.  If we can
> > defrag slab caches we can alleviate these problems.
> > 
> > Implement Slab Movable Objects in order to defragment slab caches.
> > 
> > Slab defragmentation may occur:
> > 
> > 1. Unconditionally when __kmem_cache_shrink() is called on a slab cache
> >    by the kernel calling kmem_cache_shrink().
> > 
> > 2. Unconditionally through the use of the slabinfo command.
> > 
> > 	slabinfo <cache> -s
> > 
> > 3. Conditionally via the use of kmem_cache_defrag()
> > 
> > - Use Slab Movable Objects when shrinking cache.
> > 
> > Currently when the kernel calls kmem_cache_shrink() we curate the
> > partial slabs list.  If object migration is not enabled for the cache we
> > still do this, if however, SMO is enabled we attempt to move objects in
> > partially full slabs in order to defragment the cache.  Shrink attempts
> > to move all objects in order to reduce the cache to a single partial
> > slab for each node.
> > 
> > - Add conditional per node defrag via new function:
> > 
> > 	kmem_defrag_slabs(int node).
> > 
> > kmem_defrag_slabs() attempts to defragment all slab caches for
> > node. Defragmentation is done conditionally dependent on MAX_PARTIAL
> > _and_ defrag_used_ratio.
> > 
> >    Caches are only considered for defragmentation if the number of
> >    partial slabs exceeds MAX_PARTIAL (per node).
> > 
> >    Also, defragmentation only occurs if the usage ratio of the slab is
> >    lower than the configured percentage (sysfs field added in this
> >    patch).  Fragmentation ratios are measured by calculating the
> >    percentage of objects in use compared to the total number of objects
> >    that the slab page can accommodate.
> > 
> >    The scanning of slab caches is optimized because the defragmentable
> >    slabs come first on the list. Thus we can terminate scans on the
> >    first slab encountered that does not support defragmentation.
> > 
> >    kmem_defrag_slabs() takes a node parameter. This can either be -1 if
> >    defragmentation should be performed on all nodes, or a node number.
> > 
> >    Defragmentation may be disabled by setting defrag ratio to 0
> > 
> > 	echo 0 > /sys/kernel/slab/<cache>/defrag_used_ratio
> > 
> > - Add a defrag ratio sysfs field and set it to 30% by default. A limit
> > of 30% specifies that more than 3 out of 10 available slots for objects
> > need to be in use otherwise slab defragmentation will be attempted on
> > the remaining objects.
> > 
> > In order for a cache to be defragmentable the cache must support object
> > migration (SMO).  Enabling SMO for a cache is done via a call to the
> > recently added function:
> > 
> > 	void kmem_cache_setup_mobility(struct kmem_cache *,
> > 				       kmem_cache_isolate_func,
> > 			               kmem_cache_migrate_func);
> > 
> > Co-developed-by: Christoph Lameter <cl@linux.com>
> > Signed-off-by: Tobin C. Harding <tobin@kernel.org>
> > ---
> >  Documentation/ABI/testing/sysfs-kernel-slab |  14 +
> >  include/linux/slab.h                        |   1 +
> >  include/linux/slub_def.h                    |   7 +
> >  mm/slub.c                                   | 385 ++++++++++++++++----
> >  4 files changed, 334 insertions(+), 73 deletions(-)
> 
> Hi Tobin!
> 
> Overall looks very good to me! I'll take another look when you'll post
> a non-RFC version, but so far I can't find any issues.

Thanks for the reviews.

> A generic question: as I understand, you do support only root kmemcaches now.
> Is kmemcg support in plans?

I know very little about cgroups, I have no plans for this work.
However, I'm not the architect behind this - Christoph is guiding the
direction on this one.  Perhaps he will comment.

> Without it the patchset isn't as attractive to anyone using cgroups,
> as it could be. Also, I hope it can solve (or mitigate) the memcg-specific
> problem of scattering vfs cache workingset over multiple generations of the
> same cgroup (their kmem_caches).

I'm keen to work on anything that makes this more useful so I'll do some
research.  Thanks for the idea.

Regards,
Tobin.

Re: [RFC PATCH v5 04/16] slub: Slab defrag core

[Roman Gushchin]

On Tue, May 21, 2019 at 11:15:25AM +1000, Tobin C. Harding wrote:
> On Tue, May 21, 2019 at 12:51:57AM +0000, Roman Gushchin wrote:
> > On Mon, May 20, 2019 at 03:40:05PM +1000, Tobin C. Harding wrote:
> > > Internal fragmentation can occur within pages used by the slub
> > > allocator.  Under some workloads large numbers of pages can be used by
> > > partial slab pages.  This under-utilisation is bad simply because it
> > > wastes memory but also because if the system is under memory pressure
> > > higher order allocations may become difficult to satisfy.  If we can
> > > defrag slab caches we can alleviate these problems.
> > > 
> > > Implement Slab Movable Objects in order to defragment slab caches.
> > > 
> > > Slab defragmentation may occur:
> > > 
> > > 1. Unconditionally when __kmem_cache_shrink() is called on a slab cache
> > >    by the kernel calling kmem_cache_shrink().
> > > 
> > > 2. Unconditionally through the use of the slabinfo command.
> > > 
> > > 	slabinfo <cache> -s
> > > 
> > > 3. Conditionally via the use of kmem_cache_defrag()
> > > 
> > > - Use Slab Movable Objects when shrinking cache.
> > > 
> > > Currently when the kernel calls kmem_cache_shrink() we curate the
> > > partial slabs list.  If object migration is not enabled for the cache we
> > > still do this, if however, SMO is enabled we attempt to move objects in
> > > partially full slabs in order to defragment the cache.  Shrink attempts
> > > to move all objects in order to reduce the cache to a single partial
> > > slab for each node.
> > > 
> > > - Add conditional per node defrag via new function:
> > > 
> > > 	kmem_defrag_slabs(int node).
> > > 
> > > kmem_defrag_slabs() attempts to defragment all slab caches for
> > > node. Defragmentation is done conditionally dependent on MAX_PARTIAL
> > > _and_ defrag_used_ratio.
> > > 
> > >    Caches are only considered for defragmentation if the number of
> > >    partial slabs exceeds MAX_PARTIAL (per node).
> > > 
> > >    Also, defragmentation only occurs if the usage ratio of the slab is
> > >    lower than the configured percentage (sysfs field added in this
> > >    patch).  Fragmentation ratios are measured by calculating the
> > >    percentage of objects in use compared to the total number of objects
> > >    that the slab page can accommodate.
> > > 
> > >    The scanning of slab caches is optimized because the defragmentable
> > >    slabs come first on the list. Thus we can terminate scans on the
> > >    first slab encountered that does not support defragmentation.
> > > 
> > >    kmem_defrag_slabs() takes a node parameter. This can either be -1 if
> > >    defragmentation should be performed on all nodes, or a node number.
> > > 
> > >    Defragmentation may be disabled by setting defrag ratio to 0
> > > 
> > > 	echo 0 > /sys/kernel/slab/<cache>/defrag_used_ratio
> > > 
> > > - Add a defrag ratio sysfs field and set it to 30% by default. A limit
> > > of 30% specifies that more than 3 out of 10 available slots for objects
> > > need to be in use otherwise slab defragmentation will be attempted on
> > > the remaining objects.
> > > 
> > > In order for a cache to be defragmentable the cache must support object
> > > migration (SMO).  Enabling SMO for a cache is done via a call to the
> > > recently added function:
> > > 
> > > 	void kmem_cache_setup_mobility(struct kmem_cache *,
> > > 				       kmem_cache_isolate_func,
> > > 			               kmem_cache_migrate_func);
> > > 
> > > Co-developed-by: Christoph Lameter <cl@linux.com>
> > > Signed-off-by: Tobin C. Harding <tobin@kernel.org>
> > > ---
> > >  Documentation/ABI/testing/sysfs-kernel-slab |  14 +
> > >  include/linux/slab.h                        |   1 +
> > >  include/linux/slub_def.h                    |   7 +
> > >  mm/slub.c                                   | 385 ++++++++++++++++----
> > >  4 files changed, 334 insertions(+), 73 deletions(-)
> > 
> > Hi Tobin!
> > 
> > Overall looks very good to me! I'll take another look when you'll post
> > a non-RFC version, but so far I can't find any issues.
> 
> Thanks for the reviews.
> 
> > A generic question: as I understand, you do support only root kmemcaches now.
> > Is kmemcg support in plans?
> 
> I know very little about cgroups, I have no plans for this work.
> However, I'm not the architect behind this - Christoph is guiding the
> direction on this one.  Perhaps he will comment.
> 
> > Without it the patchset isn't as attractive to anyone using cgroups,
> > as it could be. Also, I hope it can solve (or mitigate) the memcg-specific
> > problem of scattering vfs cache workingset over multiple generations of the
> > same cgroup (their kmem_caches).
> 
> I'm keen to work on anything that makes this more useful so I'll do some
> research.  Thanks for the idea.

You're welcome! I'm happy to help or even to do it by myself, once
your patches will be merged.

Thanks!

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

[Tobin C. Harding]

On Tue, May 21, 2019 at 12:57:47AM +0000, Roman Gushchin wrote:
> On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> > 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.
> 
> Hm, isn't it better to make it a static branch? Or basically anything
> that allows switching on the fly?

If that is wanted, turning SMO on and off per cache, we can probably do
this in the SMO code in SLUB.

> It seems that the cost of just building it in shouldn't be that high.
> And the question if the defragmentation worth the trouble is so much
> easier to answer if it's possible to turn it on and off without rebooting.

If the question is 'is defragmentation worth the trouble for the
dcache', I'm not sure having SMO turned off helps answer that question.
If one doesn't shrink the dentry cache there should be very little
overhead in having SMO enabled.  So if one wants to explore this
question then they can turn on the config option.  Please correct me if
I'm wrong.

The ifdef guard is there so memory management is not having any negative
effects on the dcache/VFS (no matter how small).  It also means that the
VFS guys don't have to keep an eye on what SMO is doing, they can
just configure SMO out.  The dcache is already fairly complex, I'm not
sure adding complexity to it without good reason is sound practice.  At
best SMO is only going to by mildly useful to the dcache so I feel we
should err on the side of caution.

Open to ideas.

Thanks,
Tobin.

Re: [RFC PATCH v5 13/16] slub: Enable balancing slabs across nodes

[Tobin C. Harding]

On Tue, May 21, 2019 at 01:04:10AM +0000, Roman Gushchin wrote:
> On Mon, May 20, 2019 at 03:40:14PM +1000, Tobin C. Harding wrote:
> > We have just implemented Slab Movable Objects (SMO).  On NUMA systems
> > slabs can become unbalanced i.e. many slabs on one node while other
> > nodes have few slabs.  Using SMO we can balance the slabs across all
> > the nodes.
> > 
> > The algorithm used is as follows:
> > 
> >  1. Move all objects to node 0 (this has the effect of defragmenting the
> >     cache).
> 
> This already sounds dangerous (or costly). Can't it be done without
> cross-node data moves?
>
> > 
> >  2. Calculate the desired number of slabs for each node (this is done
> >     using the approximation nr_slabs / nr_nodes).
> 
> So that on this step only (actual data size - desired data size) has
> to be moved?

This is just the most braindead algorithm I could come up with.  Surely
there are a bunch of things that could be improved.  Since I don't know
the exact use case it seemed best not to optimize for any one use case.

I'll review, comment on, and test any algorithm you come up with!

thanks,
Tobin.

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

[Roman Gushchin]

On Tue, May 21, 2019 at 11:31:18AM +1000, Tobin C. Harding wrote:
> On Tue, May 21, 2019 at 12:57:47AM +0000, Roman Gushchin wrote:
> > On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> > > 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.
> > 
> > Hm, isn't it better to make it a static branch? Or basically anything
> > that allows switching on the fly?
> 
> If that is wanted, turning SMO on and off per cache, we can probably do
> this in the SMO code in SLUB.

Not necessarily per cache, but without recompiling the kernel.
> 
> > It seems that the cost of just building it in shouldn't be that high.
> > And the question if the defragmentation worth the trouble is so much
> > easier to answer if it's possible to turn it on and off without rebooting.
> 
> If the question is 'is defragmentation worth the trouble for the
> dcache', I'm not sure having SMO turned off helps answer that question.
> If one doesn't shrink the dentry cache there should be very little
> overhead in having SMO enabled.  So if one wants to explore this
> question then they can turn on the config option.  Please correct me if
> I'm wrong.

The problem with a config option is that it's hard to switch over.

So just to test your changes in production a new kernel should be built,
tested and rolled out to a representative set of machines (which can be
measured in thousands of machines). Then if results are questionable,
it should be rolled back.

What you're actually guarding is the kmem_cache_setup_mobility() call,
which can be perfectly avoided using a boot option, for example. Turning
it on and off completely dynamic isn't that hard too.

Of course, it's up to you, it's just probably easier to find new users
of a new feature, when it's easy to test it.

Thanks!

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

[Tobin C. Harding]

On Tue, May 21, 2019 at 02:05:38AM +0000, Roman Gushchin wrote:
> On Tue, May 21, 2019 at 11:31:18AM +1000, Tobin C. Harding wrote:
> > On Tue, May 21, 2019 at 12:57:47AM +0000, Roman Gushchin wrote:
> > > On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> > > > 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.
> > > 
> > > Hm, isn't it better to make it a static branch? Or basically anything
> > > that allows switching on the fly?
> > 
> > If that is wanted, turning SMO on and off per cache, we can probably do
> > this in the SMO code in SLUB.
> 
> Not necessarily per cache, but without recompiling the kernel.
> > 
> > > It seems that the cost of just building it in shouldn't be that high.
> > > And the question if the defragmentation worth the trouble is so much
> > > easier to answer if it's possible to turn it on and off without rebooting.
> > 
> > If the question is 'is defragmentation worth the trouble for the
> > dcache', I'm not sure having SMO turned off helps answer that question.
> > If one doesn't shrink the dentry cache there should be very little
> > overhead in having SMO enabled.  So if one wants to explore this
> > question then they can turn on the config option.  Please correct me if
> > I'm wrong.
> 
> The problem with a config option is that it's hard to switch over.
> 
> So just to test your changes in production a new kernel should be built,
> tested and rolled out to a representative set of machines (which can be
> measured in thousands of machines). Then if results are questionable,
> it should be rolled back.
> 
> What you're actually guarding is the kmem_cache_setup_mobility() call,
> which can be perfectly avoided using a boot option, for example. Turning
> it on and off completely dynamic isn't that hard too.
> 
> Of course, it's up to you, it's just probably easier to find new users
> of a new feature, when it's easy to test it.

Ok, cool - I like it.  Will add for next version.

thanks,
Tobin.

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

[Tobin C. Harding]

On Tue, May 21, 2019 at 02:05:38AM +0000, Roman Gushchin wrote:
> On Tue, May 21, 2019 at 11:31:18AM +1000, Tobin C. Harding wrote:
> > On Tue, May 21, 2019 at 12:57:47AM +0000, Roman Gushchin wrote:
> > > On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> > > > 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.
> > > 
> > > Hm, isn't it better to make it a static branch? Or basically anything
> > > that allows switching on the fly?
> > 
> > If that is wanted, turning SMO on and off per cache, we can probably do
> > this in the SMO code in SLUB.
> 
> Not necessarily per cache, but without recompiling the kernel.
> > 
> > > It seems that the cost of just building it in shouldn't be that high.
> > > And the question if the defragmentation worth the trouble is so much
> > > easier to answer if it's possible to turn it on and off without rebooting.
> > 
> > If the question is 'is defragmentation worth the trouble for the
> > dcache', I'm not sure having SMO turned off helps answer that question.
> > If one doesn't shrink the dentry cache there should be very little
> > overhead in having SMO enabled.  So if one wants to explore this
> > question then they can turn on the config option.  Please correct me if
> > I'm wrong.
> 
> The problem with a config option is that it's hard to switch over.
> 
> So just to test your changes in production a new kernel should be built,
> tested and rolled out to a representative set of machines (which can be
> measured in thousands of machines). Then if results are questionable,
> it should be rolled back.
> 
> What you're actually guarding is the kmem_cache_setup_mobility() call,
> which can be perfectly avoided using a boot option, for example. Turning
> it on and off completely dynamic isn't that hard too.

Hi Roman,

I've added a boot parameter to SLUB so that admins can enable/disable
SMO at boot time system wide.  Then for each object that implements SMO
(currently XArray and dcache) I've also added a boot parameter to
enable/disable SMO for that cache specifically (these depend on SMO
being enabled system wide).

All three boot parameters default to 'off', I've added a config option
to default each to 'on'.

I've got a little more testing to do on another part of the set then the
PATCH version is coming at you :)

This is more a courtesy email than a request for comment, but please
feel free to shout if you don't like the method outlined above.

Fully dynamic config is not currently possible because currently the SMO
implementation does not support disabling mobility for a cache once it
is turned on, a bit of extra logic would need to be added and some state
stored - I'm not sure it warrants it ATM but that can be easily added
later if wanted.  Maybe Christoph will give his opinion on this.

thanks,
Tobin.

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

[Roman Gushchin]

On Wed, May 29, 2019 at 01:54:06PM +1000, Tobin C. Harding wrote:
> On Tue, May 21, 2019 at 02:05:38AM +0000, Roman Gushchin wrote:
> > On Tue, May 21, 2019 at 11:31:18AM +1000, Tobin C. Harding wrote:
> > > On Tue, May 21, 2019 at 12:57:47AM +0000, Roman Gushchin wrote:
> > > > On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> > > > > 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.
> > > > 
> > > > Hm, isn't it better to make it a static branch? Or basically anything
> > > > that allows switching on the fly?
> > > 
> > > If that is wanted, turning SMO on and off per cache, we can probably do
> > > this in the SMO code in SLUB.
> > 
> > Not necessarily per cache, but without recompiling the kernel.
> > > 
> > > > It seems that the cost of just building it in shouldn't be that high.
> > > > And the question if the defragmentation worth the trouble is so much
> > > > easier to answer if it's possible to turn it on and off without rebooting.
> > > 
> > > If the question is 'is defragmentation worth the trouble for the
> > > dcache', I'm not sure having SMO turned off helps answer that question.
> > > If one doesn't shrink the dentry cache there should be very little
> > > overhead in having SMO enabled.  So if one wants to explore this
> > > question then they can turn on the config option.  Please correct me if
> > > I'm wrong.
> > 
> > The problem with a config option is that it's hard to switch over.
> > 
> > So just to test your changes in production a new kernel should be built,
> > tested and rolled out to a representative set of machines (which can be
> > measured in thousands of machines). Then if results are questionable,
> > it should be rolled back.
> > 
> > What you're actually guarding is the kmem_cache_setup_mobility() call,
> > which can be perfectly avoided using a boot option, for example. Turning
> > it on and off completely dynamic isn't that hard too.
> 
> Hi Roman,
> 
> I've added a boot parameter to SLUB so that admins can enable/disable
> SMO at boot time system wide.  Then for each object that implements SMO
> (currently XArray and dcache) I've also added a boot parameter to
> enable/disable SMO for that cache specifically (these depend on SMO
> being enabled system wide).
> 
> All three boot parameters default to 'off', I've added a config option
> to default each to 'on'.
> 
> I've got a little more testing to do on another part of the set then the
> PATCH version is coming at you :)
> 
> This is more a courtesy email than a request for comment, but please
> feel free to shout if you don't like the method outlined above.
> 
> Fully dynamic config is not currently possible because currently the SMO
> implementation does not support disabling mobility for a cache once it
> is turned on, a bit of extra logic would need to be added and some state
> stored - I'm not sure it warrants it ATM but that can be easily added
> later if wanted.  Maybe Christoph will give his opinion on this.

Perfect!

Thanks.

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

[Tobin C. Harding]

On Wed, May 29, 2019 at 04:16:51PM +0000, Roman Gushchin wrote:
> On Wed, May 29, 2019 at 01:54:06PM +1000, Tobin C. Harding wrote:
> > On Tue, May 21, 2019 at 02:05:38AM +0000, Roman Gushchin wrote:
> > > On Tue, May 21, 2019 at 11:31:18AM +1000, Tobin C. Harding wrote:
> > > > On Tue, May 21, 2019 at 12:57:47AM +0000, Roman Gushchin wrote:
> > > > > On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> > > > > > 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.
> > > > > 
> > > > > Hm, isn't it better to make it a static branch? Or basically anything
> > > > > that allows switching on the fly?
> > > > 
> > > > If that is wanted, turning SMO on and off per cache, we can probably do
> > > > this in the SMO code in SLUB.
> > > 
> > > Not necessarily per cache, but without recompiling the kernel.
> > > > 
> > > > > It seems that the cost of just building it in shouldn't be that high.
> > > > > And the question if the defragmentation worth the trouble is so much
> > > > > easier to answer if it's possible to turn it on and off without rebooting.
> > > > 
> > > > If the question is 'is defragmentation worth the trouble for the
> > > > dcache', I'm not sure having SMO turned off helps answer that question.
> > > > If one doesn't shrink the dentry cache there should be very little
> > > > overhead in having SMO enabled.  So if one wants to explore this
> > > > question then they can turn on the config option.  Please correct me if
> > > > I'm wrong.
> > > 
> > > The problem with a config option is that it's hard to switch over.
> > > 
> > > So just to test your changes in production a new kernel should be built,
> > > tested and rolled out to a representative set of machines (which can be
> > > measured in thousands of machines). Then if results are questionable,
> > > it should be rolled back.
> > > 
> > > What you're actually guarding is the kmem_cache_setup_mobility() call,
> > > which can be perfectly avoided using a boot option, for example. Turning
> > > it on and off completely dynamic isn't that hard too.
> > 
> > Hi Roman,
> > 
> > I've added a boot parameter to SLUB so that admins can enable/disable
> > SMO at boot time system wide.  Then for each object that implements SMO
> > (currently XArray and dcache) I've also added a boot parameter to
> > enable/disable SMO for that cache specifically (these depend on SMO
> > being enabled system wide).
> > 
> > All three boot parameters default to 'off', I've added a config option
> > to default each to 'on'.
> > 
> > I've got a little more testing to do on another part of the set then the
> > PATCH version is coming at you :)
> > 
> > This is more a courtesy email than a request for comment, but please
> > feel free to shout if you don't like the method outlined above.
> > 
> > Fully dynamic config is not currently possible because currently the SMO
> > implementation does not support disabling mobility for a cache once it
> > is turned on, a bit of extra logic would need to be added and some state
> > stored - I'm not sure it warrants it ATM but that can be easily added
> > later if wanted.  Maybe Christoph will give his opinion on this.
> 
> Perfect!

Hi Roman,

I'm about to post PATCH series.  I have removed all the boot time config
options in contrast to what I stated in this thread.  I feel it requires
some comment so as not to seem rude to you.  Please feel free to
re-raise these issues on the series if you feel it is a better place to
do it than on this thread.

I still hear you re making testing easier if there are boot parameters.
I don't have extensive experience testing on a large number of machines
so I have no basis to contradict what you said.

It was suggested to me that having switches to turn SMO off implies the
series is not ready.  I am claiming that SMO _is_ ready and also that it
has no negative effects (especially on the dcache).  I therefore think
this comment is pertinent.

So ... I re-did the boot parameters defaulting to 'on'.  However I could
then see no reason (outside of testing) to turn them off.  It seems ugly
to have code that is only required during testing and never after.
Please correct me if I'm wrong.

Finally I decided that since adding a boot parameter is trivial that
hackers could easily add one to test if they wanted to test a specific
cache.  Otherwise we just test 'patched kernel' vs 'unpatched kernel'.
Again, please correct me if I'm wrong.

So, that said, please feel free to voice your opinion as strongly as you
wish.  I am super appreciative of the time you have already taken to
look at these patches.  I hope I have made the best technical decision,
and I am totally open to being told I'm wrong :)

thanks,
Tobin.

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

[Roman Gushchin]

On Mon, Jun 03, 2019 at 02:26:20PM +1000, Tobin C. Harding wrote:
> On Wed, May 29, 2019 at 04:16:51PM +0000, Roman Gushchin wrote:
> > On Wed, May 29, 2019 at 01:54:06PM +1000, Tobin C. Harding wrote:
> > > On Tue, May 21, 2019 at 02:05:38AM +0000, Roman Gushchin wrote:
> > > > On Tue, May 21, 2019 at 11:31:18AM +1000, Tobin C. Harding wrote:
> > > > > On Tue, May 21, 2019 at 12:57:47AM +0000, Roman Gushchin wrote:
> > > > > > On Mon, May 20, 2019 at 03:40:17PM +1000, Tobin C. Harding wrote:
> > > > > > > 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.
> > > > > > 
> > > > > > Hm, isn't it better to make it a static branch? Or basically anything
> > > > > > that allows switching on the fly?
> > > > > 
> > > > > If that is wanted, turning SMO on and off per cache, we can probably do
> > > > > this in the SMO code in SLUB.
> > > > 
> > > > Not necessarily per cache, but without recompiling the kernel.
> > > > > 
> > > > > > It seems that the cost of just building it in shouldn't be that high.
> > > > > > And the question if the defragmentation worth the trouble is so much
> > > > > > easier to answer if it's possible to turn it on and off without rebooting.
> > > > > 
> > > > > If the question is 'is defragmentation worth the trouble for the
> > > > > dcache', I'm not sure having SMO turned off helps answer that question.
> > > > > If one doesn't shrink the dentry cache there should be very little
> > > > > overhead in having SMO enabled.  So if one wants to explore this
> > > > > question then they can turn on the config option.  Please correct me if
> > > > > I'm wrong.
> > > > 
> > > > The problem with a config option is that it's hard to switch over.
> > > > 
> > > > So just to test your changes in production a new kernel should be built,
> > > > tested and rolled out to a representative set of machines (which can be
> > > > measured in thousands of machines). Then if results are questionable,
> > > > it should be rolled back.
> > > > 
> > > > What you're actually guarding is the kmem_cache_setup_mobility() call,
> > > > which can be perfectly avoided using a boot option, for example. Turning
> > > > it on and off completely dynamic isn't that hard too.
> > > 
> > > Hi Roman,
> > > 
> > > I've added a boot parameter to SLUB so that admins can enable/disable
> > > SMO at boot time system wide.  Then for each object that implements SMO
> > > (currently XArray and dcache) I've also added a boot parameter to
> > > enable/disable SMO for that cache specifically (these depend on SMO
> > > being enabled system wide).
> > > 
> > > All three boot parameters default to 'off', I've added a config option
> > > to default each to 'on'.
> > > 
> > > I've got a little more testing to do on another part of the set then the
> > > PATCH version is coming at you :)
> > > 
> > > This is more a courtesy email than a request for comment, but please
> > > feel free to shout if you don't like the method outlined above.
> > > 
> > > Fully dynamic config is not currently possible because currently the SMO
> > > implementation does not support disabling mobility for a cache once it
> > > is turned on, a bit of extra logic would need to be added and some state
> > > stored - I'm not sure it warrants it ATM but that can be easily added
> > > later if wanted.  Maybe Christoph will give his opinion on this.
> > 
> > Perfect!
> 
> Hi Roman,
> 
> I'm about to post PATCH series.  I have removed all the boot time config
> options in contrast to what I stated in this thread.  I feel it requires
> some comment so as not to seem rude to you.  Please feel free to
> re-raise these issues on the series if you feel it is a better place to
> do it than on this thread.
> 
> I still hear you re making testing easier if there are boot parameters.
> I don't have extensive experience testing on a large number of machines
> so I have no basis to contradict what you said.
> 
> It was suggested to me that having switches to turn SMO off implies the
> series is not ready.  I am claiming that SMO _is_ ready and also that it
> has no negative effects (especially on the dcache).  I therefore think
> this comment is pertinent.
> 
> So ... I re-did the boot parameters defaulting to 'on'.  However I could
> then see no reason (outside of testing) to turn them off.  It seems ugly
> to have code that is only required during testing and never after.
> Please correct me if I'm wrong.
> 
> Finally I decided that since adding a boot parameter is trivial that
> hackers could easily add one to test if they wanted to test a specific
> cache.  Otherwise we just test 'patched kernel' vs 'unpatched kernel'.
> Again, please correct me if I'm wrong.
> 
> So, that said, please feel free to voice your opinion as strongly as you
> wish.  I am super appreciative of the time you have already taken to
> look at these patches.  I hope I have made the best technical decision,
> and I am totally open to being told I'm wrong :)

Hi Tobin!

No boot options looks totally fine to me. I just don't like new config
options. No options at all is always the best.

Btw, thank you for this clarification!

I'll definitely try to look into the patchset on this week.

Thanks!