linux-kernel - Re: [PATCH v2] x86/sgx: Set active memcg prior to shmem allocation

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Message-ID: <CALvZod7+LyVDVvkdisSiQLySSnXjK5-VHbAwApE8TrHeUyAFxQ@mail.gmail.com>
Date:   Thu, 19 May 2022 14:22:26 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     linux-sgx@...r.kernel.org, Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        stable <stable@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2] x86/sgx: Set active memcg prior to shmem allocation

On Thu, May 19, 2022 at 2:05 PM Kristen Carlson Accardi
<kristen@...ux.intel.com> wrote:
>
> When the system runs out of enclave memory, SGX can reclaim EPC pages
> by swapping to normal RAM. These backing pages are allocated via a
> per-enclave shared memory area. Since SGX allows unlimited over
> commit on EPC memory, the reclaimer thread can allocate a large
> number of backing RAM pages in response to EPC memory pressure.
>
> When the shared memory backing RAM allocation occurs during
> the reclaimer thread context, the shared memory is charged to
> the root memory control group, and the shmem usage of the enclave
> is not properly accounted for, making cgroups ineffective at
> limiting the amount of RAM an enclave can consume.
>
> For example, when using a cgroup to launch a set of test
> enclaves, the kernel does not properly account for 50% - 75% of
> shmem page allocations on average. In the worst case, when
> nearly all allocations occur during the reclaimer thread, the
> kernel accounts less than a percent of the amount of shmem used
> by the enclave's cgroup to the correct cgroup.
>
> SGX stores a list of mm_structs that are associated with
> an enclave. Pick one of them during reclaim and charge that
> mm's memcg with the shmem allocation. The one that gets picked
> is arbitrary, but this list almost always only has one mm. The
> cases where there is more than one mm with different memcg's
> are not worth considering.
>
> Create a new function - sgx_encl_alloc_backing(). This function
> is used whenever a new backing storage page needs to be
> allocated. Previously the same function was used for page
> allocation as well as retrieving a previously allocated page.
> Prior to backing page allocation, if there is a mm_struct associated
> with the enclave that is requesting the allocation, it is set
> as the active memory control group.
>
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>

For the memcg part:

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>