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

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Message-ID: <CAKTCnzneq1JZnSQnxNBJCxJEfk65N8GPL=K6T8Lg44t7hjtV1A@mail.gmail.com>
Date:   Fri, 10 Mar 2017 08:22:28 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vladimir Davydov <vdavydov@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>
Subject: Re: [PATCH -mm -v6 2/9] mm, memcg: Support to charge/uncharge
 multiple swap entries

On Thu, Mar 9, 2017 at 12:28 PM, Huang, Ying <ying.huang@...el.com> wrote:
> Balbir Singh <bsingharora@...il.com> writes:
>
>> On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote:
>>> From: Huang Ying <ying.huang@...el.com>
>>>
>>> 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