Base dbuf cache size limit on arc_c_max

Fixes openzfs#10563

Signed-off-by: Ryan Moeller <[email protected]>

include/sys/arc_impl.h

@@ -33,6 +33,7 @@
 #include <sys/zio_crypt.h>
 #include <sys/zthr.h>
 #include <sys/aggsum.h>
+#include <sys/multilist.h>
 
 #ifdef __cplusplus
 extern "C" {

module/zfs/dbuf.c

@@ -28,6 +28,7 @@
 
 #include <sys/zfs_context.h>
 #include <sys/arc.h>
+#include <sys/arc_impl.h>
 #include <sys/dmu.h>
 #include <sys/dmu_send.h>
 #include <sys/dmu_impl.h>
@@ -207,7 +208,7 @@ typedef struct dbuf_cache {
 dbuf_cache_t dbuf_caches[DB_CACHE_MAX];
 
 /* Size limits for the caches */
-unsigned long dbuf_cache_max_bytes = 0;
+unsigned long dbuf_cache_max_bytes = ULONG_MAX;
 unsigned long dbuf_metadata_cache_max_bytes = 0;
 /* Set the default sizes of the caches to log2 fraction of arc size */
 int dbuf_cache_shift = 5;
@@ -613,8 +614,8 @@ dbuf_cache_multilist_index_func(multilist_t *ml, void *obj)
 static inline unsigned long
 dbuf_cache_target_bytes(void)
 {
-	return MIN(dbuf_cache_max_bytes,
-	    arc_target_bytes() >> dbuf_cache_shift);
+	return (MIN(dbuf_cache_max_bytes,
+	    arc_target_bytes() >> dbuf_cache_shift));
 }
 
 static inline uint64_t
@@ -807,20 +808,14 @@ dbuf_init(void)
 
 	/*
 	 * Setup the parameters for the dbuf caches. We set the sizes of the
-	 * dbuf cache and the metadata cache to 1/32nd and 1/16th (default)
-	 * of the target size of the ARC. If the values has been specified as
-	 * a module option and they're not greater than the target size of the
-	 * ARC, then we honor that value.
+	 * dbuf metadata cache to 1/16th (default) of the max size of the ARC.
+	 * If the value has been specified as a module option and it's not
+	 * greater than the max size of the ARC, then we honor that value.
 	 */
-	if (dbuf_cache_max_bytes == 0 ||
-	    dbuf_cache_max_bytes >= arc_target_bytes()) {
-		dbuf_cache_max_bytes = arc_target_bytes() >> dbuf_cache_shift;
-	}
 	if (dbuf_metadata_cache_max_bytes == 0 ||
-	    dbuf_metadata_cache_max_bytes >= arc_target_bytes()) {
+	    dbuf_metadata_cache_max_bytes >= arc_c_max)
 		dbuf_metadata_cache_max_bytes =
-		    arc_target_bytes() >> dbuf_metadata_cache_shift;
-	}
+		    arc_c_max >> dbuf_metadata_cache_shift;
 
 	/*
 	 * All entries are queued via taskq_dispatch_ent(), so min/maxalloc