Messages in this thread | | | Date | Mon, 2 Mar 2009 14:32:50 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 0/4] Memory controller soft limit patches (v3) |
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On Mon, 2 Mar 2009 10:10:43 +0530 Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-02 09:24:04]: > > > On Sun, 01 Mar 2009 11:59:59 +0530 > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > > > > > > From: Balbir Singh <balbir@linux.vnet.ibm.com>
> > > > At first, it's said "When cgroup people adds something, the kernel gets slow". > > This is my start point of reviewing. Below is comments to this version of patch. > > > > 1. I think it's bad to add more hooks to res_counter. It's enough slow to give up > > adding more fancy things.. > > res_counters was desgined to be extensible, why is adding anything to > it going to make it slow, unless we turn on soft_limits? > You inserted new "if" logic in the core loop. (What I want to say here is not that this is definitely bad but that "isn't there any alternatives which is less overhead.)
> > > > 2. please avoid to add hooks to hot-path. In your patch, especially a hook to > > mem_cgroup_uncharge_common() is annoying me. > > If soft limits are not enabled, the function does a small check and > leaves. > &soft_fail_res is passed always even if memory.soft_limit==ULONG_MAX res_counter_soft_limit_excess() adds one more function call and spinlock, and irq-off.
> > > > 3. please avoid to use global spinlock more. > > no lock is best. mutex is better, maybe. > > > > No lock to update a tree which is update concurrently? > Using tree/sort itself is nonsense, I believe.
> > 4. RB-tree seems broken. Following is example. (please note you do all ops > > in lazy manner (once in HZ/4.) > > > > i). while running, the tree is constructed as following > > > > R R=exceed=300M > > / \ > > A B A=exceed=200M B=exceed=400M > > ii) A process B exits, but and usage goes down. > > That is why we have the hook in uncharge. Even if we update and the > usage goes down, the tree is ordered by usage_in_excess which is > updated only when the tree is updated. So what you show below does not > occur. I think I should document the design better. >
time_check==true. So, update-tree at uncharge() only happens once in HZ/4 == @@ -1422,6 +1520,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype) mz = page_cgroup_zoneinfo(pc); unlock_page_cgroup(pc);
+ mem_cgroup_check_and_update_tree(mem, true); /* at swapout, this memcg will be accessed to record to swap */ if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT) css_put(&mem->css); == 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)
Thanks, -Kame
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