On Tue 26-09-17 19:06:37, Yafang Shao wrote: > 2017-09-26 18:25 GMT+08:00 Michal Hocko <mhocko@xxxxxxxxxx>: > > On Wed 20-09-17 06:43:35, Yafang Shao wrote: > >> we can find the logic in domain_dirty_limits() that > >> when dirty bg_thresh is bigger than dirty thresh, > >> bg_thresh will be set as thresh * 1 / 2. > >> if (bg_thresh >= thresh) > >> bg_thresh = thresh / 2; > >> > >> But actually we can set vm background dirtiness bigger than > >> vm dirtiness successfully. This behavior may mislead us. > >> We'd better do this validity check at the beginning. > > > > This is an admin only interface. You can screw setting this up even > > when you keep consistency between the background and direct limits. In > > general we do not try to be clever for these knobs because we _expect_ > > admins to do sane things. Why is this any different and why do we need > > to add quite some code to handle one particular corner case? > > > > Of course we expect admins to do the sane things, but not all admins > are expert or faimilar with linux kernel source code. > If we have to read the source code to know what is the right thing to > do, I don't think this is a good interface, even for the admin. Well, it is kind of natural to setup background below the direct limit in general so I am not sure what is so surprising here. Moreover setting a non default drity limits already requires some expertise. It is not like an arbitrary value will work just fine... > Anyway, there's no document on that direct limits should not less than > background limits. Then improve the documentation. > > To be honest I am not entirely sure this is worth the code and the > > future maintenance burden. > I'm not sure if this code is a burden for the future maintenance, but > I think that if we don't introduce this code it is a burden to the > admins. anytime we might need to tweak background vs direct limit we would have to change these checks as well and that sounds like a maint. burden to me. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
