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Subject: Re: [PATCH v10 3/8] hugetlb_cgroup: add reservation accounting for
 private mappings
To:     Mina Almasry <almasrymina@google.com>, rientjes@google.com,
        shakeelb@google.com
Cc:     shuah@kernel.org, gthelen@google.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org,
        aneesh.kumar@linux.vnet.ibm.com
References: <20200115012651.228058-1-almasrymina@google.com>
 <20200115012651.228058-3-almasrymina@google.com>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <49e5872e-eecb-4279-bc79-bbc1e132ab5d@oracle.com>
Date:   Fri, 17 Jan 2020 14:57:59 -0800
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On 1/14/20 5:26 PM, Mina Almasry wrote:
> Normally the pointer to the cgroup to uncharge hangs off the struct
> page, and gets queried when it's time to free the page. With
> hugetlb_cgroup reservations, this is not possible. Because it's possible
> for a page to be reserved by one task and actually faulted in by another
> task.
> 
> The best place to put the hugetlb_cgroup pointer to uncharge for
> reservations is in the resv_map. But, because the resv_map has different
> semantics for private and shared mappings, the code patch to
> charge/uncharge shared and private mappings is different. This patch
> implements charging and uncharging for private mappings.
> 
> For private mappings, the counter to uncharge is in
> resv_map->reservation_counter. On initializing the resv_map this is set
> to NULL. On reservation of a region in private mapping, the tasks
> hugetlb_cgroup is charged and the hugetlb_cgroup is placed is
> resv_map->reservation_counter.
> 
> On hugetlb_vm_op_close, we uncharge resv_map->reservation_counter.
> 
> Signed-off-by: Mina Almasry <almasrymina@google.com>

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

-- 
Mike Kravetz