linux-kernel - Re: [PATCH v12 07/14] x86/sgx: Abstract tracking reclaimable pages in LRU

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Message-ID: <e218d2aab5d793a3b4c64f90f7bad997c745ba91.camel@intel.com>
Date: Tue, 16 Apr 2024 14:07:33 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "hpa@...or.com" <hpa@...or.com>, "tim.c.chen@...ux.intel.com"
	<tim.c.chen@...ux.intel.com>, "linux-sgx@...r.kernel.org"
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	"chrisyan@...rosoft.com" <chrisyan@...rosoft.com>
Subject: Re: [PATCH v12 07/14] x86/sgx: Abstract tracking reclaimable pages in
 LRU

On Mon, 2024-04-15 at 20:20 -0700, Haitao Huang wrote:
> From: Kristen Carlson Accardi <kristen@...ux.intel.com>
> 
> The functions, sgx_{mark,unmark}_page_reclaimable(), manage the tracking
> of reclaimable EPC pages: sgx_mark_page_reclaimable() adds a newly
> allocated page into the global LRU list while
> sgx_unmark_page_reclaimable() does the opposite. Abstract the hard coded
> global LRU references in these functions to make them reusable when
> pages are tracked in per-cgroup LRUs.
> 
> Create a helper, sgx_lru_list(), that returns the LRU that tracks a given
> EPC page. It simply returns the global LRU now, and will later return
> the LRU of the cgroup within which the EPC page was allocated. Replace
> the hard coded global LRU with a call to this helper.
> 
> Next patches will first get the cgroup reclamation flow ready while
> keeping pages tracked in the global LRU and reclaimed by ksgxd before we
> make the switch in the end for sgx_lru_list() to return per-cgroup
> LRU.

I found the first paragraph hard to read.  Provide my version below for
your reference:

"
The SGX driver tracks reclaimable EPC pages via
sgx_mark_page_reclaimable(), which adds the newly allocated page into the
global LRU list.  sgx_unmark_page_reclaimable() does the opposite.

To support SGX EPC cgroup, the SGX driver will need to maintain an LRU
list for each cgroup, and the new allocated EPC page will need to be added
to the LRU of associated cgroup, but not always the global LRU list.

When sgx_mark_page_reclaimable() is called, the cgroup that the new
allocated EPC page belongs to is already known, i.e., it has been set to
the 'struct sgx_epc_page'.

Add a helper, sgx_lru_list(), to return the LRU that the EPC page should
be/is added to for the given EPC page.  Currently it just returns the
global LRU.  Change sgx_{mark|unmark}_page_reclaimable() to use the helper
function to get the LRU from the EPC page instead of referring to the
global LRU directly.

This allows EPC page being able to be tracked in "per-cgroup" LRU when
that becomes ready.
"

Nit:

That being said, is sgx_epc_page_lru() better than sgx_lru_list()?

> 
> 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>
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> Tested-by: Jarkko Sakkinen <jarkko@...nel.org>
> ---
> 

Feel free to add:

Reviewed-by: Kai Huang <kai.huang@...el.com>