MFC r274337,r274673,274681,r275515:

ZFS large block support.  The default recordsize remains at 128KB.

A new tunable/sysctl variable, vfs.zfs.max_recordsize is added to
allow adjusting the permitted maximum record size, or
zfs_max_recordsize, with a default of 1MB.  ZFS will not allow
setting recordsize greater than zfs_max_recordsize as a safety
belt, because larger recordsize means greater read and write
latency and more memory usage.

Please note that booting from datasets that have recordsize greater
than 128KB is not supported (but it's Okay to enable the feature on
the pool).

Limited safety belt is provided for mounted root filesystem but use
caution when using a larger value.

Illumos issue:
    5027 zfs large block support

1 files changed, 2 insertions, 5 deletions

diff --git a/sys/cddl/boot/zfs/zfsimpl.h b/sys/cddl/boot/zfs/zfsimpl.h
index 5f2e255..730cdf4 100644
--- a/sys/cddl/boot/zfs/zfsimpl.h
+++ b/sys/cddl/boot/zfs/zfsimpl.h
@@ -113,17 +113,14 @@
 #define	BSWAP_64(x)	((BSWAP_32(x) << 32) | BSWAP_32((x) >> 32))
 
 /*
- * We currently support nine block sizes, from 512 bytes to 128K.
- * We could go higher, but the benefits are near-zero and the cost
- * of COWing a giant block to modify one byte would become excessive.
+ * Note: the boot loader can't actually read blocks larger than 128KB,
+ * due to lack of memory.  Therefore its SPA_MAXBLOCKSIZE is still 128KB.
  */
 #define	SPA_MINBLOCKSHIFT	9
 #define	SPA_MAXBLOCKSHIFT	17
 #define	SPA_MINBLOCKSIZE	(1ULL << SPA_MINBLOCKSHIFT)
 #define	SPA_MAXBLOCKSIZE	(1ULL << SPA_MAXBLOCKSHIFT)
 
-#define	SPA_BLOCKSIZES		(SPA_MAXBLOCKSHIFT - SPA_MINBLOCKSHIFT + 1)
-
 /*
  * The DVA size encodings for LSIZE and PSIZE support blocks up to 32MB.
  * The ASIZE encoding should be at least 64 times larger (6 more bits)