(2012/06/28 19:57), Glauber Costa wrote: > On 06/28/2012 02:20 PM, Kamezawa Hiroyuki wrote: >> I think usage > limit means a sign of BUG. But, sometimes, >> res_counter_charge_nofail() is very convenient. tcp_memcg uses it. >> And I'd like to use it for helping page migration. >> >> This patch adds res_counter_usage_safe() which returns min(usage,limit). >> By this we can use res_counter_charge_nofail() without breaking >> user experience. >> >> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > I totally agree. > > It would be very nice to never go over limit, but truth is, sometimes > we're forced too - for a limited time. In those circumstances, it is > better to actually charge memcg, so the charges won't unbalance and > disappear. Every work around proposed so far for those has been to > basically add some form of "extra_charge" to the memcg, that would > effectively charge to it, but not display it. > > The good fix is in the display side. > > We should just be careful to always have good justification for no_fail > usage. It should be reserved to those situations where we really need > it, but that's on us on future reviews. > > For the idea: > > Acked-by: Glauber Costa <glommer@xxxxxxxxxxxxx> > > For the patch itself: I believe we can take the lock once in > res_counter_usage_safe, and then read the value and the limit under it. > > Calling res_counter_read_u64 two times seems not only wasteful but > potentially wrong, since they can change under our nose. > Thank you for comments. I'll update the patch using that way. Thanks, -Kame -- 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>