Persistent L2ARC

This commit makes the L2ARC persistent across reboots. We implement
a light-weight persistent L2ARC metadata structure that allows L2ARC
contents to be recovered after a reboot. This significantly eases the
impact a reboot has on read performance on systems with large caches.

Reviewed-by: Matthew Ahrens <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Co-authored-by: Saso Kiselkov <[email protected]>
Co-authored-by: Jorgen Lundman <[email protected]>
Co-authored-by: George Amanakis <[email protected]>
Ported-by: Yuxuan Shui <[email protected]>
Signed-off-by: George Amanakis <[email protected]>
Closes #925 
Closes #1823 
Closes #2672 
Closes #3744 
Closes #9582 

1 files changed, 29 insertions, 2 deletions

diff --git a/lib/libzfs/libzfs_import.c b/lib/libzfs/libzfs_import.c
index 88c4c645b..6c5f61836 100644
--- a/lib/libzfs/libzfs_import.c
+++ b/lib/libzfs/libzfs_import.c
@@ -38,6 +38,7 @@
 #include <libzfs.h>
 #include <libzfs_impl.h>
 #include <libzutil.h>
+#include <sys/arc_impl.h>
 
 /*
  * Returns true if the named pool matches the given GUID.
@@ -146,8 +147,10 @@ zpool_clear_label(int fd)
 	struct stat64 statbuf;
 	int l;
 	vdev_label_t *label;
+	l2arc_dev_hdr_phys_t *l2dhdr;
 	uint64_t size;
-	int labels_cleared = 0;
+	int labels_cleared = 0, header_cleared = 0;
+	boolean_t clear_l2arc_header = B_FALSE;
 
 	if (fstat64_blk(fd, &statbuf) == -1)
 		return (0);
@@ -157,8 +160,13 @@ zpool_clear_label(int fd)
 	if ((label = calloc(1, sizeof (vdev_label_t))) == NULL)
 		return (-1);
 
+	if ((l2dhdr = calloc(1, sizeof (l2arc_dev_hdr_phys_t))) == NULL) {
+		free(label);
+		return (-1);
+	}
+
 	for (l = 0; l < VDEV_LABELS; l++) {
-		uint64_t state, guid;
+		uint64_t state, guid, l2cache;
 		nvlist_t *config;
 
 		if (pread64(fd, label, sizeof (vdev_label_t),
@@ -185,6 +193,15 @@ zpool_clear_label(int fd)
 			continue;
 		}
 
+		/* If the device is a cache device clear the header. */
+		if (!clear_l2arc_header) {
+			if (nvlist_lookup_uint64(config,
+			    ZPOOL_CONFIG_POOL_STATE, &l2cache) == 0 &&
+			    l2cache == POOL_STATE_L2CACHE) {
+				clear_l2arc_header = B_TRUE;
+			}
+		}
+
 		nvlist_free(config);
 
 		/*
@@ -202,7 +219,17 @@ zpool_clear_label(int fd)
 		}
 	}
 
+	/* Clear the L2ARC header. */
+	if (clear_l2arc_header) {
+		memset(l2dhdr, 0, sizeof (l2arc_dev_hdr_phys_t));
+		if (pwrite64(fd, l2dhdr, sizeof (l2arc_dev_hdr_phys_t),
+		    VDEV_LABEL_START_SIZE) == sizeof (l2arc_dev_hdr_phys_t)) {
+			header_cleared++;
+		}
+	}
+
 	free(label);
+	free(l2dhdr);
 
 	if (labels_cleared == 0)
 		return (-1);