On 01/29/2013 05:46 PM, Lord Glauber Costa of Sealand wrote:
> Hi,
>
> On 01/28/2013 02:54 PM, Jeff Liu wrote:
>> As we don't account the swap stat number for the root_mem_cgroup anymore,
>> here we can just return an invalid CSS ID if there is no non-root memcg
>> is alive. Also, introduce memsw_accounting_users to track the number of
>> active non-root memcgs.
>>
>> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
>> CC: Glauber Costa <glommer@xxxxxxxxxxxxx>
>> CC: Michal Hocko <mhocko@xxxxxxx>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>> CC: Johannes Weiner <hannes@xxxxxxxxxxx>
>> CC: Mel Gorman <mgorman@xxxxxxx>
>> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> CC: Sha Zhengju <handai.szj@xxxxxxxxxx>
>>
>> ---
>> mm/page_cgroup.c | 16 +++++++++++++++-
>> 1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
>> index c945254..189fbf5 100644
>> --- a/mm/page_cgroup.c
>> +++ b/mm/page_cgroup.c
>> @@ -336,6 +336,8 @@ struct swap_cgroup {
>> };
>> #define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
>>
>> +static atomic_t memsw_accounting_users = ATOMIC_INIT(0);
>> +
>
> I am not seeing this being incremented or decremented. I can only guess
> that it comes in later patches. However, they are clearly used as a
> global reference counter.
>
> This is precisely one of the use cases static branches solve very
> neatly. Did you consider using them?
Yep, I'll try to replace it with the static branches if there are no
objections from the others. :)
Thanks,
-Jeff
>
> True, they will help a lot more when we are touching hot paths, and swap
> is hardly a hot path.
>
> However, since one of the main complaints about memcg has been that we
> inflict "death by a thousand cuts", maybe it wouldn't hurt everything
> else being the same.
>
> Michal and others, do you have any feelings here?
>
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