Use DNODE_FIND_DIRTY for SEEK_HOLE/SEEK_DATA.

There is no need to worry about txg syncs anymore, so remove
dmu_offset_next_sync and dnode_is_dirty too.

This should be transparent to userland execpt that holes created by
compression do not become visible until after the next txg sync.

mmap_seek_001_pos is updated to force a sync to match this case.

Signed-off-by: Robert Evans <[email protected]>

include/sys/dnode.h

@@ -435,7 +435,6 @@ boolean_t dnode_add_ref(dnode_t *dn, const void *ref);
 void dnode_rele(dnode_t *dn, const void *ref);
 void dnode_rele_and_unlock(dnode_t *dn, const void *tag, boolean_t evicting);
 int dnode_try_claim(objset_t *os, uint64_t object, int slots);
-boolean_t dnode_is_dirty(dnode_t *dn);
 void dnode_setdirty(dnode_t *dn, dmu_tx_t *tx);
 void dnode_set_dirtyctx(dnode_t *dn, dmu_tx_t *tx, const void *tag);
 void dnode_sync(dnode_t *dn, dmu_tx_t *tx);

module/zfs/dmu.c

@@ -75,15 +75,6 @@ static int zfs_nopwrite_enabled = 1;
  */
 static uint_t zfs_per_txg_dirty_frees_percent = 30;
 
-/*
- * Enable/disable forcing txg sync when dirty checking for holes with lseek().
- * By default this is enabled to ensure accurate hole reporting, it can result
- * in a significant performance penalty for lseek(SEEK_HOLE) heavy workloads.
- * Disabling this option will result in holes never being reported in dirty
- * files which is always safe.
- */
-static int zfs_dmu_offset_next_sync = 1;
-
 /*
  * Limit the amount we can prefetch with one call to this amount.  This
  * helps to limit the amount of memory that can be used by prefetching.
@@ -2159,45 +2150,16 @@ int
 dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
 {
 	dnode_t *dn;
-	int restarted = 0, err;
+	int err;
 
-restart:
 	err = dnode_hold(os, object, FTAG, &dn);
 	if (err)
 		return (err);
 
-	rw_enter(&dn->dn_struct_rwlock, RW_READER);
-
-	if (dnode_is_dirty(dn)) {
-		/*
-		 * If the zfs_dmu_offset_next_sync module option is enabled
-		 * then hole reporting has been requested.  Dirty dnodes
-		 * must be synced to disk to accurately report holes.
-		 *
-		 * Provided a RL_READER rangelock spanning 0-UINT64_MAX is
-		 * held by the caller only a single restart will be required.
-		 * We tolerate callers which do not hold the rangelock by
-		 * returning EBUSY and not reporting holes after one restart.
-		 */
-		if (zfs_dmu_offset_next_sync) {
-			rw_exit(&dn->dn_struct_rwlock);
-			dnode_rele(dn, FTAG);
+	err = dnode_next_offset(dn,
+	    DNODE_FIND_DIRTY | (hole ? DNODE_FIND_HOLE : 0),
+	    off, 1, 1, 0);
 
-			if (restarted)
-				return (SET_ERROR(EBUSY));
-
-			txg_wait_synced(dmu_objset_pool(os), 0);
-			restarted = 1;
-			goto restart;
-		}
-
-		err = SET_ERROR(EBUSY);
-	} else {
-		err = dnode_next_offset(dn, DNODE_FIND_HAVELOCK |
-		    (hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
-	}
-
-	rw_exit(&dn->dn_struct_rwlock);
 	dnode_rele(dn, FTAG);
 
 	return (err);
@@ -2597,9 +2559,6 @@ ZFS_MODULE_PARAM(zfs, zfs_, nopwrite_enabled, INT, ZMOD_RW,
 ZFS_MODULE_PARAM(zfs, zfs_, per_txg_dirty_frees_percent, UINT, ZMOD_RW,
 	"Percentage of dirtied blocks from frees in one TXG");
 
-ZFS_MODULE_PARAM(zfs, zfs_, dmu_offset_next_sync, INT, ZMOD_RW,
-	"Enable forcing txg sync to find holes");
-
 /* CSTYLED */
 ZFS_MODULE_PARAM(zfs, , dmu_prefetch_max, UINT, ZMOD_RW,
 	"Limit one prefetch call to this size");

module/zfs/dnode.c

@@ -1785,34 +1785,6 @@ dnode_try_claim(objset_t *os, uint64_t object, int slots)
 	    slots, NULL, NULL));
 }
 
-/*
- * Checks if the dnode itself is dirty, or is carrying any uncommitted records.
- * It is important to check both conditions, as some operations (eg appending
- * to a file) can dirty both as a single logical unit, but they are not synced
- * out atomically, so checking one and not the other can result in an object
- * appearing to be clean mid-way through a commit.
- *
- * Do not change this lightly! If you get it wrong, dmu_offset_next() can
- * detect a hole where there is really data, leading to silent corruption.
- */
-boolean_t
-dnode_is_dirty(dnode_t *dn)
-{
-	mutex_enter(&dn->dn_mtx);
-
-	for (int i = 0; i < TXG_SIZE; i++) {
-		if (multilist_link_active(&dn->dn_dirty_link[i]) ||
-		    !list_is_empty(&dn->dn_dirty_records[i])) {
-			mutex_exit(&dn->dn_mtx);
-			return (B_TRUE);
-		}
-	}
-
-	mutex_exit(&dn->dn_mtx);
-
-	return (B_FALSE);
-}
-
 void
 dnode_setdirty(dnode_t *dn, dmu_tx_t *tx)
 {

tests/zfs-tests/cmd/Makefile.am

@@ -66,6 +66,7 @@ scripts_zfs_tests_bin_PROGRAMS += %D%/mkbusy %D%/mkfile %D%/mkfiles %D%/mktree
 
 
 scripts_zfs_tests_bin_PROGRAMS += %D%/mmap_exec %D%/mmap_seek %D%/mmap_sync %D%/mmapwrite %D%/readmmap
+%C%_mmap_seek_LDADD = libzfs_core.la
 %C%_mmapwrite_LDADD = -lpthread
 
 if WANT_MMAP_LIBAIO

tests/zfs-tests/cmd/mmap_seek.c

@@ -34,6 +34,8 @@
 #ifdef __linux__
 #include <linux/fs.h>
 #endif
+#include <libnvpair.h>
+#include <libzfs_core.h>
 
 static void
 seek_data(int fd, off_t offset, off_t expected)
@@ -65,12 +67,14 @@ main(int argc, char **argv)
 	char *buf = NULL;
 	int err;
 
-	if (argc != 4) {
+	if (argc != 5) {
 		(void) printf("usage: %s <file name> <file size> "
-		    "<block size>\n", argv[0]);
+		    "<block size> <poolname>\n", argv[0]);
 		exit(1);
 	}
 
+	(void) libzfs_core_init();
+
 	int fd = open(file_path, O_RDWR | O_CREAT, 0666);
 	if (fd == -1) {
 		(void) fprintf(stderr, "%s: %s: ", execname, file_path);
@@ -80,6 +84,7 @@ main(int argc, char **argv)
 
 	off_t file_size = atoi(argv[2]);
 	off_t block_size = atoi(argv[3]);
+	const char *poolname = argv[4];
 
 	if (block_size * 2 > file_size) {
 		(void) fprintf(stderr, "file size must be at least "
@@ -133,6 +138,16 @@ main(int argc, char **argv)
 
 	/* Punch a hole (required compression be enabled). */
 	memset(buf + block_size, 0, block_size);
+	err = msync(buf, file_size, MS_SYNC);
+	if (err == -1) {
+		perror("msync");
+		exit(2);
+	}
+	err = lzc_sync(poolname, NULL, NULL);
+	if (err != 0) {
+		perror("lzc_sync");
+		exit(2);
+	}
 	seek_data(fd, 0, 0);
 	seek_data(fd, block_size, 2 * block_size);
 	seek_hole(fd, 0, block_size);

tests/zfs-tests/include/tunables.cfg

@@ -33,7 +33,6 @@ DEADMAN_FAILMODE		deadman.failmode		zfs_deadman_failmode
 DEADMAN_SYNCTIME_MS		deadman.synctime_ms		zfs_deadman_synctime_ms
 DEADMAN_ZIOTIME_MS		deadman.ziotime_ms		zfs_deadman_ziotime_ms
 DISABLE_IVSET_GUID_CHECK	disable_ivset_guid_check	zfs_disable_ivset_guid_check
-DMU_OFFSET_NEXT_SYNC		dmu_offset_next_sync		zfs_dmu_offset_next_sync
 EMBEDDED_SLOG_MIN_MS		embedded_slog_min_ms		zfs_embedded_slog_min_ms
 INITIALIZE_CHUNK_SIZE		initialize_chunk_size		zfs_initialize_chunk_size
 INITIALIZE_VALUE		initialize_value		zfs_initialize_value

tests/zfs-tests/tests/functional/mmap/mmap_seek_001_pos.ksh

@@ -43,24 +43,19 @@ function cleanup
 	log_must zfs set compression=off $TESTPOOL/$TESTFS
 	log_must zfs set recordsize=128k $TESTPOOL/$TESTFS
 	log_must rm -f $TESTDIR/test-mmap-file
-	log_must set_tunable64 DMU_OFFSET_NEXT_SYNC $dmu_offset_next_sync
 }
 
 log_assert "lseek() data/holes for an mmap()'d file."
 
 log_onexit cleanup
 
-# Enable hole reporting for dirty files.
-typeset dmu_offset_next_sync=$(get_tunable DMU_OFFSET_NEXT_SYNC)
-log_must set_tunable64 DMU_OFFSET_NEXT_SYNC 1
-
 # Compression must be enabled to convert zero'd blocks to holes.
 # This behavior is checked by the mmap_seek test.
 log_must zfs set compression=on $TESTPOOL/$TESTFS
 
 for bs in 4096 8192 16384 32768 65536 131072; do
 	log_must zfs set recordsize=$bs $TESTPOOL/$TESTFS
-	log_must mmap_seek $TESTDIR/test-mmap-file $((1024*1024)) $bs
+	log_must mmap_seek $TESTDIR/test-mmap-file $((1024*1024)) $bs $TESTPOOL
 	log_must rm $TESTDIR/test-mmap-file
 done