On Fri, 20 Aug 2010 15:50:54 +1000 Con Kolivas <kernel@xxxxxxxxxxx> wrote: > On Fri, 20 Aug 2010 02:13:25 pm KOSAKI Motohiro wrote: > > > The dirty_ratio was silently limited to >= 5%. This is not a user > > > expected behavior. Let's rip it. > > > > > > It's not likely the user space will depend on the old behavior. > > > So the risk of breaking user space is very low. > > > > > > CC: Jan Kara <jack@xxxxxxx> > > > CC: Neil Brown <neilb@xxxxxxx> > > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > > > Thank you. > > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > I have tried to do this in the past, and setting this value to 0 on some > machines caused the machine to come to a complete standstill with small > writes to disk. It seemed there was some kind of "minimum" amount of data > required by the VM before anything would make it to the disk and I never > quite found out where that blockade occurred. This was some time ago (3 years > ago) so I'm not sure if the problem has since been fixed in the VM since > then. I suggest you do some testing with this value set to zero before > approving this change. > If it is appropriate to have a lower limit, that should be imposed where the sysctl is defined in kernel/sysctl.c, not imposed after the fact where the value is used. As we now have dirty_bytes which over-rides dirty_ratio, there is little cost in having a lower_limit for dirty_ratio - it could even stay at 5% - but it really shouldn't be silent. Writing a number below the limit to the sysctl file should fail. NeilBrown -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>