[PATCH v16 12/16] x86/sgx: Revise global reclamation for EPC cgroups

[Haitao Huang <haitao.huang@linux.intel.com>]

With EPC cgroups, the global reclamation function,
sgx_reclaim_pages_global(), can no longer apply to the global LRU as
pages are now in per-cgroup LRUs.

Create a wrapper, sgx_cgroup_reclaim_global() to invoke
sgx_cgroup_reclaim_pages() passing in the root cgroup. Call this wrapper
from sgx_reclaim_pages_global() when cgroup is enabled. The wrapper will
scan and attempt to reclaim SGX_NR_TO_SCAN pages just like the current
global reclaim.

Note this simple implementation doesn't _exactly_ mimic the current
global EPC reclaim (which always tries to do the actual reclaim in batch
of SGX_NR_TO_SCAN pages): in rare cases when LRUs have less than
SGX_NR_TO_SCAN reclaimable pages, the actual reclaim of EPC pages will
be split into smaller batches _across_ multiple LRUs with each being
smaller than SGX_NR_TO_SCAN pages.

A more precise way to mimic the current global EPC reclaim would be to
have a new function to only "scan" (or "isolate") SGX_NR_TO_SCAN pages
_across_ the given EPC cgroup _AND_ its descendants, and then do the
actual reclaim in one batch.  But this is unnecessarily complicated at
this stage to address such rare cases.

Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
---
 arch/x86/kernel/cpu/sgx/epc_cgroup.c | 12 ++++++++++++
 arch/x86/kernel/cpu/sgx/epc_cgroup.h |  3 +++
 arch/x86/kernel/cpu/sgx/main.c       |  7 +++++++
 3 files changed, 22 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.c b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
index ae65cac858f8..23a61689e0d9 100644
--- a/arch/x86/kernel/cpu/sgx/epc_cgroup.c
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
@@ -240,6 +240,18 @@ static bool sgx_cgroup_should_reclaim(struct sgx_cgroup *sgx_cg)
 	return (cur >= max);
 }
 
+/**
+ * sgx_cgroup_reclaim_pages_global() - Perform one round of global reclamation.
+ *
+ * @charge_mm:	The mm to be charged for the backing store of reclaimed pages.
+ *
+ * Try to scan and attempt reclamation from root cgroup for %SGX_NR_TO_SCAN pages.
+ */
+void sgx_cgroup_reclaim_pages_global(struct mm_struct *charge_mm)
+{
+	sgx_cgroup_reclaim_pages(&sgx_cg_root, charge_mm, SGX_NR_TO_SCAN);
+}
+
 /*
  * Asynchronous work flow to reclaim pages from the cgroup when the cgroup is
  * at/near its maximum capacity.
diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.h b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
index 37364bdb797f..c0390111e28c 100644
--- a/arch/x86/kernel/cpu/sgx/epc_cgroup.h
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
@@ -36,6 +36,8 @@ static inline void __init sgx_cgroup_deinit(void) { }
 
 static inline void __init sgx_cgroup_register(void) { }
 
+static inline void sgx_cgroup_reclaim_pages_global(struct mm_struct *charge_mm) { }
+
 #else /* CONFIG_CGROUP_MISC */
 
 struct sgx_cgroup {
@@ -87,6 +89,7 @@ static inline void sgx_put_cg(struct sgx_cgroup *sgx_cg)
 
 int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_reclaim reclaim);
 void sgx_cgroup_uncharge(struct sgx_cgroup *sgx_cg);
+void sgx_cgroup_reclaim_pages_global(struct mm_struct *charge_mm);
 int __init sgx_cgroup_init(void);
 void __init sgx_cgroup_register(void);
 void __init sgx_cgroup_deinit(void);
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index fa00ed5e884d..d00cb012838b 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -411,6 +411,13 @@ static bool sgx_should_reclaim_global(unsigned long watermark)
 
 static void sgx_reclaim_pages_global(struct mm_struct *charge_mm)
 {
+	/*
+	 * Now all EPC pages are still tracked in the @sgx_global_lru.
+	 * Still reclaim from it.
+	 *
+	 * When EPC pages are tracked in the actual per-cgroup LRUs,
+	 * sgx_cgroup_reclaim_pages_global() will be called.
+	 */
 	sgx_reclaim_pages(&sgx_global_lru, charge_mm);
 }
 
-- 
2.43.0