Hi, the following patch will add:

ftp://ftp.NetBSD.org/pub/NetBSD/misc/xtraeme/syncfs_sysctl.diff

[juan@Nocturno][~]> sysctl -a|grep syncfs
kern.syncfs.syncdelay = 30
kern.syncfs.filedelay = 30
kern.syncfs.dirdelay = 15
kern.syncfs.metadelay = 10
[juan@Nocturno][~]>

It will modify the values defined in sys/miscfs/syncfs/sync_subr.c:

time_t syncdelay = 30;   /* max time to delay syncing data */
time_t filedelay = 30;     /* time to delay syncing files */ 
time_t dirdelay  = 15;     /* time to delay syncing directories */
time_t metadelay = 10;  /* time to delay syncing metadata */

FYI FreeBSD has implemented that too, but with different nodes:

kern.{dir,file,meta}_delay.

What do you think? is it useful for anyone?

Thanks.