linux-kernel - Re: [PATCH v8 06/15] x86/sgx: Abstract tracking reclaimable pages in LRU

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Message-Id: <CYU4SGK6D2BZ.3TSKS97D4OXEV@suppilovahvero>
Date: Fri, 02 Feb 2024 01:29:06 +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>
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 v8 06/15] x86/sgx: Abstract tracking reclaimable pages
 in LRU

On Tue Jan 30, 2024 at 4:09 AM EET, 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.
>
> 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>
> ---
> V7:
> - Split this out from the big patch, #10 in V6. (Dave, Kai)
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 30 ++++++++++++++++++------------
>  1 file changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 912959c7ecc9..a131aa985c95 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -32,6 +32,11 @@ static DEFINE_XARRAY(sgx_epc_address_space);
>   */
>  static struct sgx_epc_lru_list sgx_global_lru;
>  
> +static inline struct sgx_epc_lru_list *sgx_lru_list(struct sgx_epc_page *epc_page)
> +{
> +	return &sgx_global_lru;
> +}
> +
>  static atomic_long_t sgx_nr_free_pages = ATOMIC_LONG_INIT(0);
>  
>  /* Nodes with one or more EPC sections. */
> @@ -500,25 +505,24 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
>  }
>  
>  /**
> - * sgx_mark_page_reclaimable() - Mark a page as reclaimable
> + * sgx_mark_page_reclaimable() - Mark a page as reclaimable and track it in a LRU.
>   * @page:	EPC page
> - *
> - * Mark a page as reclaimable and add it to the active page list. Pages
> - * are automatically removed from the active list when freed.
>   */
>  void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
>  {
> -	spin_lock(&sgx_global_lru.lock);
> +	struct sgx_epc_lru_list *lru = sgx_lru_list(page);
> +
> +	spin_lock(&lru->lock);
>  	page->flags |= SGX_EPC_PAGE_RECLAIMER_TRACKED;
> -	list_add_tail(&page->list, &sgx_global_lru.reclaimable);
> -	spin_unlock(&sgx_global_lru.lock);
> +	list_add_tail(&page->list, &lru->reclaimable);
> +	spin_unlock(&lru->lock);
>  }
>  
>  /**
> - * sgx_unmark_page_reclaimable() - Remove a page from the reclaim list
> + * sgx_unmark_page_reclaimable() - Remove a page from its tracking LRU
>   * @page:	EPC page
>   *
> - * Clear the reclaimable flag and remove the page from the active page list.
> + * Clear the reclaimable flag if set and remove the page from its LRU.
>   *
>   * Return:
>   *   0 on success,
> @@ -526,18 +530,20 @@ void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
>   */
>  int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
>  {
> -	spin_lock(&sgx_global_lru.lock);
> +	struct sgx_epc_lru_list *lru = sgx_lru_list(page);
> +
> +	spin_lock(&lru->lock);
>  	if (page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED) {
>  		/* The page is being reclaimed. */
>  		if (list_empty(&page->list)) {
> -			spin_unlock(&sgx_global_lru.lock);
> +			spin_unlock(&lru->lock);
>  			return -EBUSY;
>  		}
>  
>  		list_del(&page->list);
>  		page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
>  	}
> -	spin_unlock(&sgx_global_lru.lock);
> +	spin_unlock(&lru->lock);
>  
>  	return 0;
>  }

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

BR, Jarkko