Add zfs_sync_pass_* tunable parameters

Commit 55d85d5a8c45c4559a4a0e675c37b0c3afb19c2f (backport of
the upstream changes) replaced three hardcoded constants:

    #define SYNC_PASS_DEFERRED_FREE 2 /* defer frees after this pass */
    #define SYNC_PASS_DONT_COMPRESS 4 /* don't compress after this pass */
    #define SYNC_PASS_REWRITE       1 /* rewrite new bps after this pass */

with a tunable parameters:

    int zfs_sync_pass_deferred_free = 2; /* defer frees starting in this pass */
    int zfs_sync_pass_dont_compress = 5; /* don't compress starting in this pass */
    int zfs_sync_pass_rewrite = 2;       /* rewrite new bps starting in this pass */

This commit makes these tunables available as module parameters
in Linux.  They should only be used for performance analysis
because changing them can result in subtle and pathological
performance problems.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1562

diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index 115d200bad0950c473ad8ae3fb1b04414f5e86af..2e1170920da3b7e56ad1a2c11daa756047d72390 100644 (file)
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -3236,4 +3236,16 @@ MODULE_PARM_DESC(zio_delay_max, "Max zio millisec delay before posting event");
 
 module_param(zio_requeue_io_start_cut_in_line, int, 0644);
 MODULE_PARM_DESC(zio_requeue_io_start_cut_in_line, "Prioritize requeued I/O");
+
+module_param(zfs_sync_pass_deferred_free, int, 0644);
+MODULE_PARM_DESC(zfs_sync_pass_deferred_free,
+    "defer frees starting in this pass");
+
+module_param(zfs_sync_pass_dont_compress, int, 0644);
+MODULE_PARM_DESC(zfs_sync_pass_dont_compress,
+    "don't compress starting in this pass");
+
+module_param(zfs_sync_pass_rewrite, int, 0644);
+MODULE_PARM_DESC(zfs_sync_pass_rewrite,
+    "rewrite new bps starting in this pass");
 #endif