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Date: Mon, 12 Feb 2024 21:35:35 +0200
Message-Id: <CZ3CPNVEG608.3LL5FU8SCDIOU@kernel.org>
From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Haitao Huang" <haitao.huang@linux.intel.com>,
 <dave.hansen@linux.intel.com>, <tj@kernel.org>, <mkoutny@suse.com>,
 <linux-kernel@vger.kernel.org>, <linux-sgx@vger.kernel.org>,
 <x86@kernel.org>, <cgroups@vger.kernel.org>, <tglx@linutronix.de>,
 <mingo@redhat.com>, <bp@alien8.de>, <hpa@zytor.com>,
 <sohil.mehta@intel.com>, <tim.c.chen@linux.intel.com>
Cc: <zhiquan1.li@intel.com>, <kristen@linux.intel.com>, <seanjc@google.com>,
 <zhanb@microsoft.com>, <anakrish@microsoft.com>,
 <mikko.ylinen@linux.intel.com>, <yangjie@microsoft.com>,
 <chrisyan@microsoft.com>
Subject: Re: [PATCH v9 08/15] x86/sgx: Implement EPC reclamation flows for
 cgroup
References: <20240205210638.157741-1-haitao.huang@linux.intel.com>
 <20240205210638.157741-9-haitao.huang@linux.intel.com>
In-Reply-To: <20240205210638.157741-9-haitao.huang@linux.intel.com>

On Mon Feb 5, 2024 at 11:06 PM EET, Haitao Huang wrote:
> From: Kristen Carlson Accardi <kristen@linux.intel.com>
>
> Implement the reclamation flow for cgroup, encapsulated in the top-level
> function sgx_epc_cgroup_reclaim_pages(). It does a pre-order walk on its
> subtree, and make calls to sgx_reclaim_pages() at each node passing in
> the LRU of that node. It keeps track of total reclaimed pages, and pages
> left to attempt.  It stops the walk if desired number of pages are
> attempted.
>
> In some contexts, e.g. page fault handling, only asynchronous
> reclamation is allowed. Create a work-queue, corresponding work item and
> function definitions to support the asynchronous reclamation. Both
> synchronous and asynchronous flows invoke the same top level reclaim
> function, and will be triggered later by sgx_epc_cgroup_try_charge()
> when usage of the cgroup is at or near its limit.
>
> Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> Co-developed-by: Haitao Huang <haitao.huang@linux.intel.com>
> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
> ---
> V9:
> - Add comments for static variables. (Jarkko)
>
> V8:
> - Remove alignment for substructure variables. (Jarkko)
>
> V7:
> - Split this out from the big patch, #10 in V6. (Dave, Kai)
> ---
>  arch/x86/kernel/cpu/sgx/epc_cgroup.c | 181 ++++++++++++++++++++++++++-
>  arch/x86/kernel/cpu/sgx/epc_cgroup.h |   3 +
>  2 files changed, 183 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.c b/arch/x86/kernel/cpu/s=
gx/epc_cgroup.c
> index f4a37ace67d7..16b6d9f909eb 100644
> --- a/arch/x86/kernel/cpu/sgx/epc_cgroup.c
> +++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
> @@ -8,9 +8,180 @@
>  /* The root EPC cgroup */
>  static struct sgx_epc_cgroup epc_cg_root;
> =20
> +/*
> + * The work queue that reclaims EPC pages in the background for cgroups.
> + *
> + * A cgroup schedules a work item into this queue to reclaim pages withi=
n the
> + * same cgroup when its usage limit is reached and synchronous reclamati=
on is not
> + * an option, e.g., in a fault handler.
> + */

Here I get a bit confused of the text because of "e.g., in a fault
handler".  Can we enumerate sites broadly where stimulus could
happen.

Does not have to be complete but at least the most common locations
would make this comment *actually* useful for later maintenance.

BR, Jarkko