From aebc96831f152a9da5f2c919103d571e80d3fade Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Thu, 5 Nov 2020 03:25:23 +0000
Subject: [PATCH] zfs: lz4: add optional kmem_alloc support

lz4 port from illumos to Linux added a 16KB per-CPU cache to accommodate for
the missing 16KB malloc. FreeBSD supports this size, making the extra cache
harmful as it can't share buckets.
---
 sys/contrib/openzfs/module/zfs/lz4.c | 61 ++++++++++++++++++++++++++--
 1 file changed, 57 insertions(+), 4 deletions(-)

diff --git a/sys/contrib/openzfs/module/zfs/lz4.c b/sys/contrib/openzfs/module/zfs/lz4.c
index 4b46e694891a..9da9d9e00635 100644
--- a/sys/contrib/openzfs/module/zfs/lz4.c
+++ b/sys/contrib/openzfs/module/zfs/lz4.c
@@ -44,7 +44,8 @@ static int LZ4_compressCtx(void *ctx, const char *source, char *dest,
 static int LZ4_compress64kCtx(void *ctx, const char *source, char *dest,
     int isize, int osize);
 
-static kmem_cache_t *lz4_cache;
+static void *lz4_alloc(int flags);
+static void lz4_free(void *ctx);
 
 /*ARGSUSED*/
 size_t
@@ -838,8 +839,7 @@ real_LZ4_compress(const char *source, char *dest, int isize, int osize)
 	void *ctx;
 	int result;
 
-	ASSERT(lz4_cache != NULL);
-	ctx = kmem_cache_alloc(lz4_cache, KM_SLEEP);
+	ctx = lz4_alloc(KM_SLEEP);
 
 	/*
 	 * out of kernel memory, gently fall through - this will disable
@@ -855,7 +855,7 @@ real_LZ4_compress(const char *source, char *dest, int isize, int osize)
 	else
 		result = LZ4_compressCtx(ctx, source, dest, isize, osize);
 
-	kmem_cache_free(lz4_cache, ctx);
+	lz4_free(ctx);
 	return (result);
 }
 
@@ -1014,6 +1014,23 @@ LZ4_uncompress_unknownOutputSize(const char *source, char *dest, int isize,
 	return (-1);
 }
 
+#ifdef __FreeBSD__
+/*
+ * FreeBSD has 4, 8 and 16 KB malloc zones which can be used here.
+ * Should struct refTables get resized this may need to be revisited, hence
+ * compiler-time asserts.
+ */
+_Static_assert(sizeof(struct refTables) <= 16384,
+    "refTables too big for malloc");
+_Static_assert((sizeof(struct refTables) % 4096) == 0,
+    "refTables not a multiple of page size");
+#else
+#define ZFS_LZ4_USE_CACHE
+#endif
+
+#ifdef ZFS_LZ4_USE_CACHE
+static kmem_cache_t *lz4_cache;
+
 void
 lz4_init(void)
 {
@@ -1029,3 +1046,39 @@ lz4_fini(void)
 		lz4_cache = NULL;
 	}
 }
+
+static void *
+lz4_alloc(int flags)
+{
+	ASSERT(lz4_cache != NULL);
+	return (kmem_cache_alloc(lz4_cache, flags));
+}
+
+static void
+lz4_free(void *ctx)
+{
+	kmem_cache_free(lz4_cache, ctx);
+}
+#else
+void
+lz4_init(void)
+{
+}
+
+void
+lz4_fini(void)
+{
+}
+
+static void *
+lz4_alloc(int flags)
+{
+	return (kmem_alloc(sizeof (struct refTables), flags));
+}
+
+static void
+lz4_free(void *ctx)
+{
+	kmem_free(ctx, sizeof (struct refTables));
+}
+#endif