[Devel] Re: [PATCH 8/15] Helpers to find the task by its numerical ids

[Pavel Emelyanov]

Oleg Nesterov wrote:
> On 07/26, Pavel Emelyanov wrote:
>> +#define find_pid(pid)	find_pid_ns(pid, &init_pid_ns)
> 
> Again, I think find_pid() should use current's active ns, not
> init_pid_ns. Just grep for find_pid/find_task_by_pid.
> 
>> --- linux-2.6.23-rc1-mm1.orig/kernel/pid.c	2007-07-26 16:34:45.000000000 +0400
>> +++ linux-2.6.23-rc1-mm1-7/kernel/pid.c	2007-07-26 16:36:37.000000000 +0400
>> @@ -204,19 +221,20 @@ static void delayed_put_pid(struct rcu_h
>>  	goto out;
>>  }
>>
>> -struct pid * fastcall find_pid(int nr)
>> +struct pid * fastcall find_pid_ns(int nr, struct pid_namespace *ns)
>>  {
>>  	struct hlist_node *elem;
>> -	struct pid *pid;
>> +	struct upid *pnr;
>> +
>> +	hlist_for_each_entry_rcu(pnr, elem,
>> +			&pid_hash[pid_hashfn(nr, ns)], pid_chain)
>> +		if (pnr->nr == nr && pnr->ns == ns)
>                                      ^^^^^^^^^^^^^
> Aha, that is why we need upid->ns.

That's it :)

> I am a bit surprised we don't move the global pid_hash into the
> "struct pid_namespace", this could speedup the search, and we
> don't need upid->ns.

Hm... Worth thinking about, but this hash itself is large enough and
its size depends on the node's number of pages, so we'll have

1. either to make per-namespace hash (much) smaller;
2. or to give (too) many memory for it.

>> -struct pid *find_ge_pid(int nr)
>> +struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
>>  {
>>  	struct pid *pid;
>>
>>  	do {
>> -		pid = find_pid(nr);
>> +		pid = find_pid_ns(nr, ns);
>>  		if (pid)
>>  			break;
>> -		nr = next_pidmap(task_active_pid_ns(current), nr);
>> +		nr = next_pidmap(ns, nr);
>>  	} while (nr > 0);
>>
>>  	return pid;
> 
> This means we should fix the caller, next_tgid(), but this is done
> in 15/15.

Sorry :)

> Oleg.
> 
> 

Thank,
Pavel