Expose zfetch_max_idistance tunable

FreeBSD had this value tunable before the switch to the new OpenZFS. The tunable name has changed, breaking legacy compat. Restore legacy compat for this tunable, properly expose the tunable with the new name on all platforms, and document it in zfs-module-parameters(5). While here, clean up the documentation for zfetch_max_distance a bit. Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Ryan Moeller <[email protected]> Closes openzfs#11038
sempervictus · May 31, 2021 · 2bf963c · 2bf963c
1 parent cf86650
commit 2bf963c
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Showing 3 changed files with 20 additions and 5 deletions.
diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
@@ -827,9 +827,20 @@ Default value: \fB1,048,576\fR.
 \fBzfetch_max_distance\fR (uint)
 .ad
 .RS 12n
-Max bytes to prefetch per stream (default 8MB).
+Max bytes to prefetch per stream.
 .sp
-Default value: \fB8,388,608\fR.
+Default value: \fB8,388,608\fR (8MB).
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfetch_max_idistance\fR (uint)
+.ad
+.RS 12n
+Max bytes to prefetch indirects for per stream.
+.sp
+Default vaule: \fB67,108,864\fR (64MB).
 .RE
 
 .sp

diff --git a/module/os/freebsd/zfs/sysctl_os.c b/module/os/freebsd/zfs/sysctl_os.c
@@ -300,8 +300,9 @@ SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_distance, CTLFLAG_RWTUN,
 
 /* max bytes to prefetch indirects for per stream (default 64MB) */
 extern uint32_t	zfetch_max_idistance;
-SYSCTL_UINT(_vfs_zfs_prefetch, OID_AUTO, max_idistance, CTLFLAG_RWTUN,
-    &zfetch_max_idistance, 0, "Max bytes to prefetch indirects for per stream");
+SYSCTL_UINT(_vfs_zfs_zfetch, OID_AUTO, max_idistance, CTLFLAG_RWTUN,
+    &zfetch_max_idistance, 0,
+    "Max bytes to prefetch indirects for per stream (LEGACY)");
 
 /* dsl_pool.c */
 

diff --git a/module/zfs/dmu_zfetch.c b/module/zfs/dmu_zfetch.c
@@ -457,7 +457,10 @@ ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, min_sec_reap, UINT, ZMOD_RW,
 	"Min time before stream reclaim");
 
 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_distance, UINT, ZMOD_RW,
-	"Max bytes to prefetch per stream (default 8MB)");
+	"Max bytes to prefetch per stream");
+
+ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, max_idistance, UINT, ZMOD_RW,
+	"Max bytes to prefetch indirects for per stream");
 
 ZFS_MODULE_PARAM(zfs_prefetch, zfetch_, array_rd_sz, ULONG, ZMOD_RW,
 	"Number of bytes in a array_read");