Re: [PATCH -mm -v6 2/9] mm, memcg: Support to charge/uncharge multiple swap entries

[Balbir Singh]

On Thu, Mar 9, 2017 at 12:28 PM, Huang, Ying <ying.huang@xxxxxxxxx> wrote:
> Balbir Singh <bsingharora@xxxxxxxxx> writes:
>
>> On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote:
>>> From: Huang Ying <ying.huang@xxxxxxxxx>
>>>
>>> This patch make it possible to charge or uncharge a set of continuous
>>> swap entries in the swap cgroup.  The number of swap entries is
>>> specified via an added parameter.
>>>
>>> This will be used for the THP (Transparent Huge Page) swap support.
>>> Where a swap cluster backing a THP may be allocated and freed as a
>>> whole.  So a set of (HPAGE_PMD_NR) continuous swap entries backing one
>>> THP need to be charged or uncharged together.  This will batch the
>>> cgroup operations for the THP swap too.
>>
>> A quick look at the patches makes it look sane. I wonder if we would
>> make sense to track THP swapout separately as well
>> (from a memory.stat perspective)
>
> The patchset is just the first step of THP swap optimization.  So the
> THP will still be split after putting the THP into the swap cache.  This
> makes it unnecessary to change mem_cgroup_swapout().  I am working on a
> following up patchset to further delaying THP splitting after swapping
> out the THP to the disk.  In that patchset, I will change
> mem_cgroup_swapout() too.


Fair enough

Thanks,
Balbir