On Mon, Mar 11, 2013 at 6:57 PM, Andrew Morton
<a...@linux-foundation.org> wrote:
> On Mon, 11 Mar 2013 18:18:56 -0300 "Raphael S. Carvalho"
> <raphael.sc...@gmail.com> wrote:
>
>> From: Raphael S.Carvalho <raphael.sc...@gmail.com>
>>
>> Notes: find_next_offset searches for an available "cleaned bit"
>> in the respective pid bitmap (page), so returns the offset if found,
>> otherwise it returns a value equals to BITS_PER_PAGE.
>>
>> For example, suppose find_next_offset didn't find any available
>> bit, so there's no purpose to call mk_pid (Wasteful Cpu Cycles).
>>
>> Therefore, I found it could be better to call mk_pid after
>> the checking (offset < BITS_PER_PAGE) returned sucessfully!
>> Another point: If (offset < BITS_PER_PAGE) results in a "failure",
>> then mk_pid would be called again afterwards.
>>
>> ...
>>
>> --- a/kernel/pid.c
>> +++ b/kernel/pid.c
>> @@ -190,8 +190,8 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
>> return pid;
>> }
>> offset = find_next_offset(map, offset);
>> - pid = mk_pid(pid_ns, map, offset);
>> - } while (offset < BITS_PER_PAGE && pid < pid_max);
>> + } while (offset < BITS_PER_PAGE &&
>> + (pid = mk_pid(pid_ns, map, offset)) < pid_max);
>> }
>> if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
>> ++map;
>
> Looks OK. But I think it's simpler and more straightforward to do it
> this way?
Yes, it looks much better.
>
> for ( ; ; ) {
> if (!test_and_set_bit(offset, map->page)) {
> atomic_dec(&map->nr_free);
> set_last_pid(pid_ns, last, pid);
> return pid;
> }
> offset = find_next_offset(map, offset);
> if (offset >= BITS_PER_PAGE)
> break;
> pid = mk_pid(pid_ns, map, offset);
> if (pid >= pid_max)
> break;
> }
>
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