lkml.org 
[lkml]   [2009]   [Mar]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/4] Memory controller soft limit patches (v3)
On Mon, 2 Mar 2009 23:22:35 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-02 15:18:30]:
>
> > On Mon, 2 Mar 2009 11:35:19 +0530
> > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> >
> > > > Then, not-sorted RB-tree can be there.
> > > >
> > > > BTW,
> > > > time_after(jiffies, 0)
> > > > is buggy (see definition). If you want make this true always,
> > > > time_after(jiffies, jiffies +1)
> > > >
> > >
> > > HZ/4 is 250/4 jiffies in the worst case (62). We have
> > > time_after(jiffies, next_update_interval) and next_update_interval is
> > > set to last_tree_update + 62. Not sure if I got what you are pointing
> > > to.
> > >
> > + unsigned long next_update = 0;
> > + unsigned long flags;
> > +
> > + if (!css_tryget(&mem->css))
> > + return;
> > + prev_usage_in_excess = mem->usage_in_excess;
> > + new_usage_in_excess = res_counter_soft_limit_excess(&mem->res);
> > +
> > + if (time_check)
> > + next_update = mem->last_tree_update +
> > + MEM_CGROUP_TREE_UPDATE_INTERVAL;
> > + if (new_usage_in_excess && time_after(jiffies, next_update)) {
> > + if (prev_usage_in_excess)
> > + mem_cgroup_remove_exceeded(mem);
> > + mem_cgroup_insert_exceeded(mem);
> > + updated_tree = true;
> > + } else if (prev_usage_in_excess && !new_usage_in_excess) {
> > + mem_cgroup_remove_exceeded(mem);
> > + updated_tree = true;
> > + }
> >
> > My point is what happens if time_check==false.
> > time_afrter(jiffies, 0) is buggy.
> >
>
> I see your point now, but the idea behind doing so is that
> time_after(jiffies, 0) will always return false, which forces the
> prev_usage_in_excess and !new_usage_in_excess check to execute. We set
> the value to false only from __mem_cgroup_free().
>
> Are you suggesting that calling time_after(jiffies, 0) is buggy?
> The comment
>
> Do this with "<0" and ">=0" to only test the sign of the result. A
>
> I think refers to the comparison check and not to the parameters. I
> hope I am reading this right.

106 #define time_after(a,b) \
107 (typecheck(unsigned long, a) && \
108 typecheck(unsigned long, b) && \
109 ((long)(b) - (long)(a) < 0))

Reading above.

if b==0.
if (long)a <0 -> false
if (long)a >0 -> true
jiffies is unsigned value. please think of bit-pattern of signed/unsigned value.


Thanks,
-Kame








\
 
 \ /
  Last update: 2009-03-03 01:07    [from the cache]
©2003-2011 Jasper Spaans