linux-kernel - Re: [PATCH v9 08/15] x86/sgx: Implement EPC reclamation flows for cgroup

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Date: Mon, 12 Feb 2024 21:35:35 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Haitao Huang" <haitao.huang@...ux.intel.com>,
 <dave.hansen@...ux.intel.com>, <tj@...nel.org>, <mkoutny@...e.com>,
 <linux-kernel@...r.kernel.org>, <linux-sgx@...r.kernel.org>,
 <x86@...nel.org>, <cgroups@...r.kernel.org>, <tglx@...utronix.de>,
 <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
 <sohil.mehta@...el.com>, <tim.c.chen@...ux.intel.com>
Cc: <zhiquan1.li@...el.com>, <kristen@...ux.intel.com>, <seanjc@...gle.com>,
 <zhanb@...rosoft.com>, <anakrish@...rosoft.com>,
 <mikko.ylinen@...ux.intel.com>, <yangjie@...rosoft.com>,
 <chrisyan@...rosoft.com>
Subject: Re: [PATCH v9 08/15] x86/sgx: Implement EPC reclamation flows for
 cgroup

On Mon Feb 5, 2024 at 11:06 PM EET, Haitao Huang wrote:
> From: Kristen Carlson Accardi <kristen@...ux.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@...el.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Co-developed-by: Haitao Huang <haitao.huang@...ux.intel.com>
> Signed-off-by: Haitao Huang <haitao.huang@...ux.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/sgx/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;
>  
> +/*
> + * The work queue that reclaims EPC pages in the background for cgroups.
> + *
> + * A cgroup schedules a work item into this queue to reclaim pages within the
> + * same cgroup when its usage limit is reached and synchronous reclamation 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