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 <[email protected]>
Sponsored-by: https://github.com/sponsors/robn

3 files changed, 123 insertions, 4 deletions

diff --git a/module/Kbuild.in b/module/Kbuild.in
index b9c284a24..f1a145779 100644
--- a/module/Kbuild.in
+++ b/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 \
diff --git a/module/os/linux/spl/spl-shrinker.c b/module/os/linux/spl/spl-shrinker.c
new file mode 100644
index 000000000..d5c8da471
--- /dev/null
+++ b/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 <[email protected]>.
+ *  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);
diff --git a/module/os/linux/zfs/arc_os.c b/module/os/linux/zfs/arc_os.c
index 43ed087e2..1fa9f3eb3 100644
--- a/module/os/linux/zfs/arc_os.c
+++ b/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,
-    arc_shrinker_count, arc_shrinker_scan, DEFAULT_SEEKS);
+static struct shrinker *arc_shrinker = NULL;
 
 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