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

From: Shakeel Butt <shakeelb@google.com>
To: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: linux-sgx@vger.kernel.org, Jarkko Sakkinen <jarkko@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	stable <stable@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>, Michal Hocko <mhocko@suse.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH v2] x86/sgx: Set active memcg prior to shmem allocation
Date: Thu, 19 May 2022 14:22:26 -0700	[thread overview]
Message-ID: <CALvZod7+LyVDVvkdisSiQLySSnXjK5-VHbAwApE8TrHeUyAFxQ@mail.gmail.com> (raw)
In-Reply-To: <20220519210445.5310-1-kristen@linux.intel.com>

On Thu, May 19, 2022 at 2:05 PM Kristen Carlson Accardi
<kristen@linux.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@linux.intel.com>

For the memcg part:

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