linux 6.7 compat: rework shrinker setup for heap allocations

6.7 changes the shrinker API such that shrinkers must be allocated
dynamically by the kernel. To accomodate this, this commit reworks
spl_register_shrinker() to do something similar against earlier kernels.

Signed-off-by: Rob Norris <robn@despairlabs.com>
Sponsored-by: https://github.com/sponsors/robn

config/kernel-shrink.m4

@@ -128,6 +128,25 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK], [
 	])
 ])
 
+dnl #
+dnl # 6.7 API change
+dnl # register_shrinker has been replaced by shrinker_register.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER_REGISTER], [
+	ZFS_LINUX_TEST_SRC([shrinker_register], [
+		#include <linux/shrinker.h>
+		unsigned long shrinker_cb(struct shrinker *shrink,
+		    struct shrink_control *sc) { return 0; }
+	],[
+		struct shrinker cache_shrinker = {
+			.count_objects = shrinker_cb,
+			.scan_objects = shrinker_cb,
+			.seeks = DEFAULT_SEEKS,
+		};
+		shrinker_register(&cache_shrinker);
+	])
+])
+
 AC_DEFUN([ZFS_AC_KERNEL_SHRINKER_CALLBACK],[
 	dnl #
 	dnl # 6.0 API change
@@ -165,18 +184,40 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINKER_CALLBACK],[
 			dnl # cs->shrink() is logically split in to
 			dnl # cs->count_objects() and cs->scan_objects()
 			dnl #
-			AC_MSG_CHECKING([if cs->count_objects callback exists])
+			AC_MSG_CHECKING(
+			    [whether cs->count_objects callback exists])
 			ZFS_LINUX_TEST_RESULT(
 			    [shrinker_cb_shrink_control_split],[
 				AC_MSG_RESULT(yes)
 				AC_DEFINE(HAVE_SPLIT_SHRINKER_CALLBACK, 1,
 				    [cs->count_objects exists])
 			],[
+				AC_MSG_RESULT(no)
+
+				AC_MSG_CHECKING(
+				    [whether shrinker_register exists])
+				ZFS_LINUX_TEST_RESULT([shrinker_register], [
+					AC_MSG_RESULT(yes)
+					AC_DEFINE(HAVE_SHRINKER_REGISTER, 1,
+					    [shrinker_register exists])
+
+					dnl # We assume that the split shrinker
+					dnl # callback exists if
+					dnl # shrinker_register() exists,
+					dnl # because the latter is a much more
+					dnl # recent addition, and the macro
+					dnl # test for shrinker_register() only
+					dnl # works if the callback is split
+					AC_DEFINE(HAVE_SPLIT_SHRINKER_CALLBACK,
+					    1, [cs->count_objects exists])
+				],[
+					AC_MSG_RESULT(no)
 					ZFS_LINUX_TEST_ERROR([shrinker])
 				])
 			])
 		])
 	])
+])
 
 dnl #
 dnl # 2.6.39 API change,
@@ -211,6 +252,7 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER], [
 	ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK
 	ZFS_AC_KERNEL_SRC_SHRINK_CONTROL_STRUCT
 	ZFS_AC_KERNEL_SRC_REGISTER_SHRINKER_VARARG
+	ZFS_AC_KERNEL_SRC_SHRINKER_REGISTER
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_SHRINKER], [

include/os/linux/spl/sys/shrinker.h

@@ -29,12 +29,13 @@
 
 /*
  * Due to frequent changes in the shrinker API the following
- * compatibility wrappers should be used.  They are as follows:
+ * compatibility wrapper should be used.
  *
- *   SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost);
+ *   shrinker = spl_register_shrinker(name, countfunc, scanfunc, seek_cost);
+ *   spl_unregister_shrinker(shrinker);
  *
- * SPL_SHRINKER_DECLARE is used to declare a shrinker with the name varname,
+ * spl_register_shrinker is used to create and register a shrinker with the
- * which is passed to spl_register_shrinker()/spl_unregister_shrinker().
+ * given name.
  * The countfunc returns the number of free-able objects.
  * The scanfunc returns the number of objects that were freed.
  * The callbacks can return SHRINK_STOP if further calls can't make any more
@@ -57,57 +58,28 @@
  *	...scan objects in the cache and reclaim them...
  * }
  *
- * SPL_SHRINKER_DECLARE(my_shrinker, my_count, my_scan, DEFAULT_SEEKS);
+ * static struct shrinker *my_shrinker;
  *
  * void my_init_func(void) {
- *	spl_register_shrinker(&my_shrinker);
+ *	my_shrinker = spl_register_shrinker("my-shrinker",
+ *	    my_count, my_scan, DEFAULT_SEEKS);
+ * }
+ *
+ * void my_fini_func(void) {
+ *	spl_unregister_shrinker(my_shrinker);
  * }
  */
 
-#ifdef HAVE_REGISTER_SHRINKER_VARARG
+typedef unsigned long (*spl_shrinker_cb)
-#define	spl_register_shrinker(x)	register_shrinker(x, "zfs-arc-shrinker")
+	(struct shrinker *, struct shrink_control *);
-#else
-#define	spl_register_shrinker(x)	register_shrinker(x)
-#endif
-#define	spl_unregister_shrinker(x)	unregister_shrinker(x)
 
-/*
+struct shrinker *spl_register_shrinker(const char *name,
- * Linux 3.0 to 3.11 Shrinker API Compatibility.
+    spl_shrinker_cb countfunc, spl_shrinker_cb scanfunc, int seek_cost);
- */
+void spl_unregister_shrinker(struct shrinker *);
-#if defined(HAVE_SINGLE_SHRINKER_CALLBACK)
-#define	SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost)	\
-static int								\
-__ ## varname ## _wrapper(struct shrinker *shrink, struct shrink_control *sc)\
-{									\
-	if (sc->nr_to_scan != 0) {					\
-		(void) scanfunc(shrink, sc);				\
-	}								\
-	return (countfunc(shrink, sc));					\
-}									\
-									\
-static struct shrinker varname = {					\
-	.shrink = __ ## varname ## _wrapper,				\
-	.seeks = seek_cost,						\
-}
 
+#ifndef SHRINK_STOP
+/* 3.0-3.11 compatibility */
 #define	SHRINK_STOP	(-1)
-
-/*
- * Linux 3.12 and later Shrinker API Compatibility.
- */
-#elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
-#define	SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost)	\
-static struct shrinker varname = {					\
-	.count_objects = countfunc,					\
-	.scan_objects = scanfunc,					\
-	.seeks = seek_cost,						\
-}
-
-#else
-/*
- * Linux 2.x to 2.6.22, or a newer shrinker API has been introduced.
- */
-#error "Unknown shrinker callback"
 #endif
 
 #endif /* SPL_SHRINKER_H */

module/Kbuild.in

@@ -79,6 +79,7 @@ SPL_OBJS := \
 	spl-kstat.o \
 	spl-proc.o \
 	spl-procfs-list.o \
+	spl-shrinker.o \
 	spl-taskq.o \
 	spl-thread.o \
 	spl-trace.o \

module/os/linux/spl/spl-shrinker.c

@@ -0,0 +1,115 @@
+/*
+ *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
+ *  Copyright (C) 2007 The Regents of the University of California.
+ *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
+ *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
+ *  UCRL-CODE-235197
+ *
+ *  This file is part of the SPL, Solaris Porting Layer.
+ *
+ *  The SPL is free software; you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the
+ *  Free Software Foundation; either version 2 of the License, or (at your
+ *  option) any later version.
+ *
+ *  The SPL is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ *  for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *  Solaris Porting Layer (SPL) Shrinker Implementation.
+ */
+
+#include <sys/kmem.h>
+#include <sys/shrinker.h>
+
+#ifdef HAVE_SINGLE_SHRINKER_CALLBACK
+/* 3.0-3.11: single shrink() callback, which we wrap to carry both functions */
+struct spl_shrinker_wrap {
+	struct shrinker shrinker;
+	spl_shrinker_cb countfunc;
+	spl_shrinker_cb scanfunc;
+};
+
+static int
+spl_shrinker_single_cb(struct shrinker *shrinker, struct shrink_control *sc)
+{
+	struct spl_shrinker_wrap *sw = (struct spl_shrinker_wrap *)shrinker;
+
+	if (sc->nr_to_scan != 0)
+		(void) sw->scanfunc(&sw->shrinker, sc);
+	return (sw->countfunc(&sw->shrinker, sc));
+}
+#endif
+
+struct shrinker *
+spl_register_shrinker(const char *name, spl_shrinker_cb countfunc,
+    spl_shrinker_cb scanfunc, int seek_cost)
+{
+	struct shrinker *shrinker;
+
+	/* allocate shrinker */
+#if defined(HAVE_SHRINKER_REGISTER)
+	/* 6.7: kernel will allocate the shrinker for us */
+	shrinker = shrinker_alloc(0, name);
+#elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
+	/* 3.12-6.6: we allocate the shrinker  */
+	shrinker = kmem_zalloc(sizeof (struct shrinker), KM_SLEEP);
+#elif defined(HAVE_SINGLE_SHRINKER_CALLBACK)
+	/* 3.0-3.11: allocate a wrapper */
+	struct spl_shrinker_wrap *sw =
+	    kmem_zalloc(sizeof (struct spl_shrinker_wrap), KM_SLEEP);
+	shrinker = &sw->shrinker;
+#else
+	/* 2.x-2.6.22, or a newer shrinker API has been introduced. */
+#error "Unknown shrinker API"
+#endif
+
+	if (shrinker == NULL)
+		return (NULL);
+
+	/* set callbacks */
+#ifdef HAVE_SINGLE_SHRINKER_CALLBACK
+	sw->countfunc = countfunc;
+	sw->scanfunc = scanfunc;
+	shrinker->shrink = spl_shrinker_single_cb;
+#else
+	shrinker->count_objects = countfunc;
+	shrinker->scan_objects = scanfunc;
+#endif
+
+	/* set params */
+	shrinker->seeks = seek_cost;
+
+	/* register with kernel */
+#if defined(HAVE_SHRINKER_REGISTER)
+	shrinker_register(shrinker);
+#elif defined(HAVE_REGISTER_SHRINKER_VARARG)
+	register_shrinker(shrinker, name);
+#else
+	register_shrinker(shrinker);
+#endif
+
+	return (shrinker);
+}
+EXPORT_SYMBOL(spl_register_shrinker);
+
+void
+spl_unregister_shrinker(struct shrinker *shrinker)
+{
+#if defined(HAVE_SHRINKER_REGISTER)
+	shrinker_free(shrinker);
+#elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
+	unregister_shrinker(shrinker);
+	kmem_free(shrinker, sizeof (struct shrinker));
+#elif defined(HAVE_SINGLE_SHRINKER_CALLBACK)
+	unregister_shrinker(shrinker);
+	kmem_free(shrinker, sizeof (struct spl_shrinker_wrap));
+#else
+#error "Unknown shrinker API"
+#endif
+}
+EXPORT_SYMBOL(spl_unregister_shrinker);

module/os/linux/zfs/arc_os.c

@@ -247,8 +247,7 @@ arc_shrinker_scan(struct shrinker *shrink, struct shrink_control *sc)
 	return (sc->nr_to_scan);
 }
 
-SPL_SHRINKER_DECLARE(arc_shrinker,
+static struct shrinker *arc_shrinker = NULL;
-    arc_shrinker_count, arc_shrinker_scan, DEFAULT_SEEKS);
 
 int
 arc_memory_throttle(spa_t *spa, uint64_t reserve, uint64_t txg)
@@ -351,14 +350,18 @@ arc_lowmem_init(void)
 	 * reclaim from the arc.  This is done to prevent kswapd from
 	 * swapping out pages when it is preferable to shrink the arc.
 	 */
-	spl_register_shrinker(&arc_shrinker);
+	arc_shrinker = spl_register_shrinker("zfs-arc-shrinker",
+	    arc_shrinker_count, arc_shrinker_scan, DEFAULT_SEEKS);
+	VERIFY(arc_shrinker);
+
 	arc_set_sys_free(allmem);
 }
 
 void
 arc_lowmem_fini(void)
 {
-	spl_unregister_shrinker(&arc_shrinker);
+	spl_unregister_shrinker(arc_shrinker);
+	arc_shrinker = NULL;
 }
 
 int