spa_load_verify() may consume too much memory

When a pool is imported it will scan the pool to verify the integrity 
of the data and metadata. The amount it scans will depend on the 
import flags provided. On systems with small amounts of memory or 
when importing a pool from the crash kernel, it's possible for 
spa_load_verify to issue too many I/Os that it consumes all the memory 
of the system resulting in an OOM message or a hang.

To prevent this, we limit the amount of memory that the initial pool
scan can consume. This change will, by default, use 1/16th of the ARC
for scan I/Os to prevent running the system out of memory during import.

Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Signed-off-by: George Wilson george.wilson@delphix.com
External-issue: DLPX-65237
External-issue: DLPX-65238
Closes #9146

cmd/zdb/zdb.c

@@ -111,7 +111,7 @@ typedef void object_viewer_t(objset_t *, uint64_t, void *data, size_t size);
 
 uint64_t *zopt_object = NULL;
 static unsigned zopt_objects = 0;
-uint64_t max_inflight = 1000;
+uint64_t max_inflight_bytes = 256 * 1024 * 1024; /* 256MB */
 static int leaked_objects = 0;
 static range_tree_t *mos_refd_objs;
 
@@ -3806,7 +3806,7 @@ zdb_blkptr_done(zio_t *zio)
 	abd_free(zio->io_abd);
 
 	mutex_enter(&spa->spa_scrub_lock);
-	spa->spa_load_verify_ios--;
+	spa->spa_load_verify_bytes -= BP_GET_PSIZE(bp);
 	cv_broadcast(&spa->spa_scrub_io_cv);
 
 	if (ioerr && !(zio->io_flags & ZIO_FLAG_SPECULATIVE)) {
@@ -3877,9 +3877,9 @@ zdb_blkptr_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 			flags |= ZIO_FLAG_SPECULATIVE;
 
 		mutex_enter(&spa->spa_scrub_lock);
-		while (spa->spa_load_verify_ios > max_inflight)
+		while (spa->spa_load_verify_bytes > max_inflight_bytes)
 			cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
-		spa->spa_load_verify_ios++;
+		spa->spa_load_verify_bytes += size;
 		mutex_exit(&spa->spa_scrub_lock);
 
 		zio_nowait(zio_read(NULL, spa, bp, abd, size,
@@ -4895,6 +4895,7 @@ dump_block_stats(spa_t *spa)
 			    ZIO_FLAG_GODFATHER);
 		}
 	}
+	ASSERT0(spa->spa_load_verify_bytes);
 
 	/*
 	 * Done after zio_wait() since zcb_haderrors is modified in
@@ -6681,10 +6682,10 @@ main(int argc, char **argv)
 			break;
 		/* NB: Sort single match options below. */
 		case 'I':
-			max_inflight = strtoull(optarg, NULL, 0);
-			if (max_inflight == 0) {
+			max_inflight_bytes = strtoull(optarg, NULL, 0);
+			if (max_inflight_bytes == 0) {
 				(void) fprintf(stderr, "maximum number "
-				    "of inflight I/Os must be greater "
+				    "of inflight bytes must be greater "
 				    "than 0\n");
 				usage();
 			}

include/sys/spa_impl.h

@@ -272,7 +272,9 @@ struct spa {
 	boolean_t	spa_extreme_rewind;	/* rewind past deferred frees */
 	kmutex_t	spa_scrub_lock;		/* resilver/scrub lock */
 	uint64_t	spa_scrub_inflight;	/* in-flight scrub bytes */
-	uint64_t	spa_load_verify_ios;	/* in-flight verification IOs */
+
+	/* in-flight verification bytes */
+	uint64_t	spa_load_verify_bytes;
 	kcondvar_t	spa_scrub_io_cv;	/* scrub I/O completion */
 	uint8_t		spa_scrub_active;	/* active or suspended? */
 	uint8_t		spa_scrub_type;		/* type of scrub we're doing */

man/man5/zfs-module-parameters.5

@@ -543,13 +543,13 @@ Default value: \fB1\fR.
 .sp
 .ne 2
 .na
-\fBspa_load_verify_maxinflight\fR (int)
+\fBspa_load_verify_shift\fR (int)
 .ad
 .RS 12n
-Maximum concurrent I/Os during the traversal performed during an "extreme
-rewind" (\fB-X\fR) pool import.
+Sets the maximum number of bytes to consume during pool import to the log2
+fraction of the target arc size.
 .sp
-Default value: \fB10000\fR.
+Default value: \fB4\fR.
 .RE
 
 .sp

module/zfs/spa.c

@@ -90,6 +90,7 @@
 #include <sys/fm/util.h>
 #include <sys/callb.h>
 #include <sys/zone.h>
+#include <sys/vmsystm.h>
 #endif	/* _KERNEL */
 
 #include "zfs_prop.h"
@@ -2197,16 +2198,16 @@ spa_load_verify_done(zio_t *zio)
 	}
 
 	mutex_enter(&spa->spa_scrub_lock);
-	spa->spa_load_verify_ios--;
+	spa->spa_load_verify_bytes -= BP_GET_PSIZE(bp);
 	cv_broadcast(&spa->spa_scrub_io_cv);
 	mutex_exit(&spa->spa_scrub_lock);
 }
 
 /*
- * Maximum number of concurrent scrub i/os to create while verifying
- * a pool while importing it.
+ * Maximum number of inflight bytes is the log2 faction of the arc size.
+ * By default, we set it to 1/16th of the arc.
  */
-int spa_load_verify_maxinflight = 10000;
+int spa_load_verify_shift = 4;
 int spa_load_verify_metadata = B_TRUE;
 int spa_load_verify_data = B_TRUE;
 
@@ -2228,13 +2229,14 @@ spa_load_verify_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	if (!BP_IS_METADATA(bp) && !spa_load_verify_data)
 		return (0);
 
+	int maxinflight_bytes = arc_target_bytes() >> spa_load_verify_shift;
 	zio_t *rio = arg;
 	size_t size = BP_GET_PSIZE(bp);
 
 	mutex_enter(&spa->spa_scrub_lock);
-	while (spa->spa_load_verify_ios >= spa_load_verify_maxinflight)
+	while (spa->spa_load_verify_bytes >= maxinflight_bytes)
 		cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
-	spa->spa_load_verify_ios++;
+	spa->spa_load_verify_bytes += size;
 	mutex_exit(&spa->spa_scrub_lock);
 
 	zio_nowait(zio_read(rio, spa, bp, abd_alloc_for_io(size, B_FALSE), size,
@@ -2287,12 +2289,14 @@ spa_load_verify(spa_t *spa)
 			    "spa_load_verify_metadata=%u)",
 			    spa_load_verify_data, spa_load_verify_metadata);
 		}
+
 		error = traverse_pool(spa, spa->spa_verify_min_txg,
 		    TRAVERSE_PRE | TRAVERSE_PREFETCH_METADATA |
 		    TRAVERSE_NO_DECRYPT, spa_load_verify_cb, rio);
 	}
 
 	(void) zio_wait(rio);
+	ASSERT0(spa->spa_load_verify_bytes);
 
 	spa->spa_load_meta_errors = sle.sle_meta_count;
 	spa->spa_load_data_errors = sle.sle_data_count;
@@ -9309,9 +9313,11 @@ EXPORT_SYMBOL(spa_event_notify);
 #endif
 
 #if defined(_KERNEL)
-module_param(spa_load_verify_maxinflight, int, 0644);
-MODULE_PARM_DESC(spa_load_verify_maxinflight,
-	"Max concurrent traversal I/Os while verifying pool during import -X");
+/* BEGIN CSTYLED */
+module_param(spa_load_verify_shift, int, 0644);
+MODULE_PARM_DESC(spa_load_verify_shift, "log2(fraction of arc that can "
+	"be used by inflight I/Os when verifying pool during import");
+/* END CSTYLED */
 
 module_param(spa_load_verify_metadata, int, 0644);
 MODULE_PARM_DESC(spa_load_verify_metadata,