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. -- 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>