Message-Id: <CYLIOR19J0SG.2A6LWMNXTERV9@suppilovahvero>
Date: Mon, 22 Jan 2024 22:28:31 +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>
Subject: Re: [PATCH v7 07/15] x86/sgx: Expose sgx_reclaim_pages() for cgroup

On Mon Jan 22, 2024 at 7:20 PM EET, Haitao Huang wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
>
> Each EPC cgroup will have an LRU structure to track reclaimable EPC pages.
> When a cgroup usage reaches its limit, the cgroup needs to reclaim pages
> from its LRU or LRUs of its descendants to make room for any new
> allocations.
>
> To prepare for reclamation per cgroup, expose the top level reclamation
> function, sgx_reclaim_pages(), in header file for reuse. Add a parameter
> to the function to pass in an LRU so cgroups can pass in different
> tracking LRUs later.  Add another parameter for passing in the number of
> pages to scan and make the function return the number of pages reclaimed
> as a cgroup reclaimer may need to track reclamation progress from its
> descendants, change number of pages to scan in subsequent calls.
>
> Create a wrapper for the global reclaimer, sgx_reclaim_pages_global(),
> to just call this function with the global LRU passed in. When
> per-cgroup LRU is added later, the wrapper will perform global
> reclamation from the root cgroup.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Co-developed-by: Kristen Carlson Accardi <kristen@...ux.intel.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:
> - Reworked from patch 9 of V6, "x86/sgx: Restructure top-level EPC reclaim
> function". Do not split the top level function (Kai)
> - Dropped patches 7 and 8 of V6.
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 62 +++++++++++++++++++++-------------
>  arch/x86/kernel/cpu/sgx/sgx.h  |  1 +
>  2 files changed, 40 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index cde750688e62..60cb3a7b3001 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -286,20 +286,24 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
>  	mutex_unlock(&encl->lock);
>  }
>  
> -/*
> - * Take a fixed number of pages from the head of the active page pool and
> - * reclaim them to the enclave's private shmem files. Skip the pages, which have
> - * been accessed since the last scan. Move those pages to the tail of active
> - * page pool so that the pages get scanned in LRU like fashion.
> +/**
> + * sgx_reclaim_pages() - Reclaim a fixed number of pages from an LRU
> + *
> + * Take a fixed number of pages from the head of a given LRU and reclaim them to the enclave's
> + * private shmem files. Skip the pages, which have been accessed since the last scan. Move
> + * those pages to the tail of the list so that the pages get scanned in LRU like fashion.
> + *
> + * Batch process a chunk of pages (at the moment 16) in order to degrade amount of IPI's and
> + * ETRACK's potentially required. sgx_encl_ewb() does degrade a bit among the HW threads with
> + * three stage EWB pipeline (EWB, ETRACK + EWB and IPI + EWB) but not sufficiently. Reclaiming
> + * one page at a time would also be problematic as it would increase the lock contention too
> + * much, which would halt forward progress.
>   *

I'd prefer 80 character paragraphs unless you absolutely need to go
beyond that. For normal text paragraph there's zero need.


> - * Batch process a chunk of pages (at the moment 16) in order to degrade amount
> - * of IPI's and ETRACK's potentially required. sgx_encl_ewb() does degrade a bit
> - * among the HW threads with three stage EWB pipeline (EWB, ETRACK + EWB and IPI
> - * + EWB) but not sufficiently. Reclaiming one page at a time would also be
> - * problematic as it would increase the lock contention too much, which would
> - * halt forward progress.
> + * @lru:	The LRU from which pages are reclaimed.
> + * @nr_to_scan: Pointer to the target number of pages to scan, must be less than SGX_NR_TO_SCAN.
> + * Return:	Number of pages reclaimed.
>   */
> -static void sgx_reclaim_pages(void)
> +unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to_scan)
>  {
>  	struct sgx_epc_page *chunk[SGX_NR_TO_SCAN];
>  	struct sgx_backing backing[SGX_NR_TO_SCAN];
> @@ -310,10 +314,10 @@ static void sgx_reclaim_pages(void)
>  	int ret;
>  	int i;
>  
> -	spin_lock(&sgx_global_lru.lock);
> -	for (i = 0; i < SGX_NR_TO_SCAN; i++) {
> -		epc_page = list_first_entry_or_null(&sgx_global_lru.reclaimable,
> -						    struct sgx_epc_page, list);
> +	spin_lock(&lru->lock);
> +
> +	for (; *nr_to_scan > 0; --(*nr_to_scan)) {
> +		epc_page = list_first_entry_or_null(&lru->reclaimable, struct sgx_epc_page, list);
>  		if (!epc_page)
>  			break;
>  
> @@ -328,7 +332,8 @@ static void sgx_reclaim_pages(void)
>  			 */
>  			epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
>  	}
> -	spin_unlock(&sgx_global_lru.lock);
> +
> +	spin_unlock(&lru->lock);
>  
>  	for (i = 0; i < cnt; i++) {
>  		epc_page = chunk[i];
> @@ -351,9 +356,9 @@ static void sgx_reclaim_pages(void)
>  		continue;
>  
>  skip:
> -		spin_lock(&sgx_global_lru.lock);
> -		list_add_tail(&epc_page->list, &sgx_global_lru.reclaimable);
> -		spin_unlock(&sgx_global_lru.lock);
> +		spin_lock(&lru->lock);
> +		list_add_tail(&epc_page->list, &lru->reclaimable);
> +		spin_unlock(&lru->lock);
>  
>  		kref_put(&encl_page->encl->refcount, sgx_encl_release);
>  
> @@ -366,6 +371,7 @@ static void sgx_reclaim_pages(void)
>  			sgx_reclaimer_block(epc_page);
>  	}
>  
> +	ret = 0;
>  	for (i = 0; i < cnt; i++) {
>  		epc_page = chunk[i];
>  		if (!epc_page)
> @@ -378,7 +384,10 @@ static void sgx_reclaim_pages(void)
>  		epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
>  
>  		sgx_free_epc_page(epc_page);
> +		ret++;
>  	}
> +
> +	return (unsigned int)ret;
>  }
>  
>  static bool sgx_should_reclaim(unsigned long watermark)
> @@ -387,6 +396,13 @@ static bool sgx_should_reclaim(unsigned long watermark)
>  	       !list_empty(&sgx_global_lru.reclaimable);
>  }
>  
> +static void sgx_reclaim_pages_global(void)
> +{
> +	unsigned int nr_to_scan = SGX_NR_TO_SCAN;
> +
> +	sgx_reclaim_pages(&sgx_global_lru, &nr_to_scan);
> +}
> +
>  /*
>   * sgx_reclaim_direct() should be called (without enclave's mutex held)
>   * in locations where SGX memory resources might be low and might be
> @@ -395,7 +411,7 @@ static bool sgx_should_reclaim(unsigned long watermark)
>  void sgx_reclaim_direct(void)
>  {
>  	if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
> -		sgx_reclaim_pages();
> +		sgx_reclaim_pages_global();
>  }
>  
>  static int ksgxd(void *p)
> @@ -418,7 +434,7 @@ static int ksgxd(void *p)
>  				     sgx_should_reclaim(SGX_NR_HIGH_PAGES));
>  
>  		if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
> -			sgx_reclaim_pages();
> +			sgx_reclaim_pages_global();
>  
>  		cond_resched();
>  	}
> @@ -605,7 +621,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
>  		 * Need to do a global reclamation if cgroup was not full but free
>  		 * physical pages run out, causing __sgx_alloc_epc_page() to fail.
>  		 */
> -		sgx_reclaim_pages();
> +		sgx_reclaim_pages_global();
>  		cond_resched();
>  	}
>  
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 0e99e9ae3a67..2593c013d091 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -110,6 +110,7 @@ void sgx_reclaim_direct(void);
>  void sgx_mark_page_reclaimable(struct sgx_epc_page *page);
>  int sgx_unmark_page_reclaimable(struct sgx_epc_page *page);
>  struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim);
> +unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to_scan);
>  
>  void sgx_ipi_cb(void *info);
>  

BR, Jarkko

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