On Tue, Aug 10, 2010 at 11:57:12AM +0800, Neil Brown wrote: > On Tue, 10 Aug 2010 12:12:06 +0900 (JST) > KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote: > > > > Subject: writeback: explicit low bound for vm.dirty_ratio > > > From: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > > Date: Thu Jul 15 10:28:57 CST 2010 > > > > > > Force a user visible low bound of 5% for the vm.dirty_ratio interface. > > > > > > This is an interface change. When doing > > > > > > echo N > /proc/sys/vm/dirty_ratio > > > > > > where N < 5, the old behavior is pretend to accept the value, while > > > the new behavior is to reject it explicitly with -EINVAL. This will > > > possibly break user space if they checks the return value. > > > > Umm.. I dislike this change. Is there any good reason to refuse explicit > > admin's will? Why 1-4% is so bad? Internal clipping can be changed later > > but explicit error behavior is hard to change later. > > As a data-point, I had a situation a while back where I needed a value below > 1 to get desired behaviour. The system had lots of RAM and fairly slow > write-back (over NFS) so a 'sync' could take minutes. Jan, here is a use case to limit dirty pages on slow devices :) > So I would much prefer allowing not only 1-4, but also fraction values!!! > > I can see no justification at all for setting a lower bound of 5. Even zero > can be useful - for testing purposes mostly. Neil, that's perfectly legitimate need which I overlooked. It seems that the vm.dirty_bytes parameter will work for your case. Thanks, Fengguang -- 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>