sgx_reclaim_direct() was introduced to preemptively reclaim some pages as the best effort to avoid on-demand reclamation that can stall forward progress in some situations, e.g., allocating pages to load previously reclaimed page to perform EDMM operations on [1]. Currently when the global usage is close to the capacity, sgx_reclaim_direct() makes one invocation to sgx_reclaim_pages_global() but does not guarantee there are free pages available for later allocations to succeed. In other words, the only goal here is to reduce the chance of on-demand reclamation at allocation time. In cases of allocation failure, the caller, the EDMM ioctl()'s, would return -EAGAIN to user space and let the user space to decide whether to retry or not. With EPC cgroups enabled, usage of a cgroup can also reach its limit (usually much lower than capacity) and trigger per-cgroup reclamation. Implement a similar strategy to reduce the chance of on-demand per-cgroup reclamation for this use case. Create a wrapper, sgx_cgroup_reclaim_direct(), to perform a preemptive reclamation at cgroup level, and have sgx_reclaim_direct() call it when EPC cgroup is enabled. [1] https://lore.kernel.org/all/a0d8f037c4a075d56bf79f432438412985f7ff7a.1652137848.git.reinette.chatre@xxxxxxxxx/T/#u Signed-off-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx> --- arch/x86/kernel/cpu/sgx/epc_cgroup.c | 15 +++++++++++++++ arch/x86/kernel/cpu/sgx/epc_cgroup.h | 3 +++ arch/x86/kernel/cpu/sgx/main.c | 4 ++++ 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 23a61689e0d9..b7d60b2d878d 100644 --- a/arch/x86/kernel/cpu/sgx/epc_cgroup.c +++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c @@ -252,6 +252,21 @@ void sgx_cgroup_reclaim_pages_global(struct mm_struct *charge_mm) sgx_cgroup_reclaim_pages(&sgx_cg_root, charge_mm, SGX_NR_TO_SCAN); } +/** + * sgx_cgroup_reclaim_direct() - Preemptive reclamation. + * + * Scan and attempt to reclaim %SGX_NR_TO_SCAN as best effort to allow caller + * make quick progress. + */ +void sgx_cgroup_reclaim_direct(void) +{ + struct sgx_cgroup *sgx_cg = sgx_get_current_cg(); + + if (sgx_cgroup_should_reclaim(sgx_cg)) + sgx_cgroup_reclaim_pages(sgx_cg, current->mm, SGX_NR_TO_SCAN); + sgx_put_cg(sgx_cg); +} + /* * 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 c0390111e28c..cf2b946d993e 100644 --- a/arch/x86/kernel/cpu/sgx/epc_cgroup.h +++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h @@ -38,6 +38,8 @@ static inline void __init sgx_cgroup_register(void) { } static inline void sgx_cgroup_reclaim_pages_global(struct mm_struct *charge_mm) { } +static inline void sgx_cgroup_reclaim_direct(void) { } + #else /* CONFIG_CGROUP_MISC */ struct sgx_cgroup { @@ -90,6 +92,7 @@ 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); +void sgx_cgroup_reclaim_direct(void); 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 d00cb012838b..9a8f91ebd21b 100644 --- a/arch/x86/kernel/cpu/sgx/main.c +++ b/arch/x86/kernel/cpu/sgx/main.c @@ -428,6 +428,10 @@ static void sgx_reclaim_pages_global(struct mm_struct *charge_mm) */ void sgx_reclaim_direct(void) { + /* Reduce chance of per-cgroup reclamation for later allocation */ + sgx_cgroup_reclaim_direct(); + + /* Reduce chance of the global reclamation for later allocation */ if (sgx_should_reclaim_global(SGX_NR_LOW_PAGES)) sgx_reclaim_pages_global(current->mm); } -- 2.43.0
