writeback: explicit low bound for vm.dirty_ratio
in [Kernel]
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From: Wu Fengguang on 10 Aug 2010 14:20 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(a)jp.fujitsu.com> wrote: > > > > Subject: writeback: explicit low bound for vm.dirty_ratio > > > From: Wu Fengguang <fengguang.wu(a)intel.com> > > > 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |