linux-kernel - Re: [PATCH v2 13/18] x86/sgx: Add helper to grab pages from an arbitrary EPC LRU

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Date:   Thu, 8 Dec 2022 09:56:57 +0000
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     dave.hansen@...ux.intel.com, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        zhiquan1.li@...el.com, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v2 13/18] x86/sgx: Add helper to grab pages from an
 arbitrary EPC LRU

On Fri, Dec 02, 2022 at 10:36:49AM -0800, Kristen Carlson Accardi wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> Move the isolation loop into a standalone helper, sgx_isolate_pages(),
> in preparation for existence of multiple LRUs.  Expose the helper to
> other SGX code so that it can be called from the EPC cgroup code, e.g.
> to isolate pages from a single cgroup LRU.  Exposing the isolation loop
> allows the cgroup iteration logic to be wholly encapsulated within the
> cgroup code.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 68 +++++++++++++++++++++-------------
>  arch/x86/kernel/cpu/sgx/sgx.h  |  2 +
>  2 files changed, 44 insertions(+), 26 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index c947b4ae06f3..a59550fa150b 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -280,7 +280,46 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
>  }
>  
>  /**
> - * sgx_reclaim_pages() - Reclaim EPC pages from the consumers
> + * sgx_isolate_epc_pages() - Isolate pages from an LRU for reclaim
> + * @lru:	LRU from which to reclaim
> + * @nr_to_scan:	Number of pages to scan for reclaim
> + * @dst:	Destination list to hold the isolated pages
> + */
> +void sgx_isolate_epc_pages(struct sgx_epc_lru_lists *lru, int *nr_to_scan,
> +			   struct list_head *dst)

Why not instead return the number of pages scanned, and pass
'int nr_to_scan'?

That would just be more idiomatic choice.

BR, Jarkko