zfsonlinux/zfs — pull request #1562 by imp (2013-07-02 08:57:11+00:00)
Title: New tunable parameters

While the new tunables are not intended for day-to-day tweak, it is the question of parity with Illumos - if the need to tinker with these variable ever arise the Linux way of doing so is module parameter.

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.