Re: [PATCH v12 08/14] x86/sgx: Add basic EPC reclamation flow for cgroup
On Wed, 17 Apr 2024 18:51:28 -0500, Huang, Kai wrote: On 16/04/2024 3:20 pm, Haitao Huang wrote: From: Kristen Carlson Accardi Currently in the EPC page allocation, the kernel simply fails the allocation when the current EPC cgroup fails to charge due to its usage reaching limit. This is not ideal. When that happens, a better way is to reclaim EPC page(s) from the current EPC cgroup (and/or its descendants) to reduce its usage so the new allocation can succeed. Add the basic building blocks to support per-cgroup reclamation. Currently the kernel only has one place to reclaim EPC pages: the global EPC LRU list. To support the "per-cgroup" EPC reclaim, maintain an LRU list for each EPC cgroup, and introduce a "cgroup" variant function to reclaim EPC pages from a given EPC cgroup and its descendants. Currently the kernel does the global EPC reclaim in sgx_reclaim_page(). It always tries to reclaim EPC pages in batch of SGX_NR_TO_SCAN (16) pages. Specifically, it always "scans", or "isolates" SGX_NR_TO_SCAN pages from the global LRU, and then tries to reclaim these pages at once for better performance. Implement the "cgroup" variant EPC reclaim in a similar way, but keep the implementation simple: 1) change sgx_reclaim_pages() to take an LRU as input, and return the pages that are "scanned" and attempted for reclamation (but not necessarily reclaimed successfully); 2) loop the given EPC cgroup and its descendants and do the new sgx_reclaim_pages() until SGX_NR_TO_SCAN pages are "scanned". This implementation, encapsulated in sgx_cgroup_reclaim_pages(), always tries to reclaim SGX_NR_TO_SCAN pages from the LRU of the given EPC cgroup, and only moves to its descendants when there's no enough reclaimable EPC pages to "scan" in its LRU. It should be enough for most cases. 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): 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. Alternatively, the current sgx_reclaim_pages() could be changed to return the actual "reclaimed" pages, but not "scanned" pages. However, the reclamation is a lengthy process, forcing a successful reclamation of predetermined number of pages may block the caller for too long. And that may not be acceptable in some synchronous contexts, e.g., in serving an ioctl(). With this building block in place, add synchronous reclamation support in sgx_cgroup_try_charge(): trigger a call to sgx_cgroup_reclaim_pages() if the cgroup reaches its limit and the caller allows synchronous reclaim as indicated by s newly added parameter. A later patch will add support for asynchronous reclamation reusing sgx_cgroup_reclaim_pages(). Note all reclaimable EPC pages are still tracked in the global LRU thus no per-cgroup reclamation is actually active at the moment. Per-cgroup tracking and reclamation will be turned on in the end after all necessary infrastructure is in place. Nit: "all necessary infrastructures are in place", or, "all necessary building blocks are in place". ? Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Signed-off-by: Kristen Carlson Accardi Co-developed-by: Haitao Huang Signed-off-by: Haitao Huang Tested-by: Jarkko Sakkinen --- Reviewed-by: Kai Huang Thanks More nitpickings below: [...] -static inline int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg) +static inline int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_reclaim reclaim) Let's still wrap the text on 80-character basis. I guess most people are more used to that. [...] - epc_page = list_first_entry_or_null(_global_lru.reclaimable, - struct sgx_epc_page, list); + epc_page = list_first_entry_or_null(>reclaimable, struct sgx_epc_page, list); Ditto. Actually I changed to 100 char width based on comments from Jarkko IIRC. I don't have personal preference, but will not change back to 80 unless Jarkko also agrees. Thanks Haitao
Re: [PATCH v12 08/14] x86/sgx: Add basic EPC reclamation flow for cgroup
On 16/04/2024 3:20 pm, Haitao Huang wrote: From: Kristen Carlson Accardi Currently in the EPC page allocation, the kernel simply fails the allocation when the current EPC cgroup fails to charge due to its usage reaching limit. This is not ideal. When that happens, a better way is to reclaim EPC page(s) from the current EPC cgroup (and/or its descendants) to reduce its usage so the new allocation can succeed. Add the basic building blocks to support per-cgroup reclamation. Currently the kernel only has one place to reclaim EPC pages: the global EPC LRU list. To support the "per-cgroup" EPC reclaim, maintain an LRU list for each EPC cgroup, and introduce a "cgroup" variant function to reclaim EPC pages from a given EPC cgroup and its descendants. Currently the kernel does the global EPC reclaim in sgx_reclaim_page(). It always tries to reclaim EPC pages in batch of SGX_NR_TO_SCAN (16) pages. Specifically, it always "scans", or "isolates" SGX_NR_TO_SCAN pages from the global LRU, and then tries to reclaim these pages at once for better performance. Implement the "cgroup" variant EPC reclaim in a similar way, but keep the implementation simple: 1) change sgx_reclaim_pages() to take an LRU as input, and return the pages that are "scanned" and attempted for reclamation (but not necessarily reclaimed successfully); 2) loop the given EPC cgroup and its descendants and do the new sgx_reclaim_pages() until SGX_NR_TO_SCAN pages are "scanned". This implementation, encapsulated in sgx_cgroup_reclaim_pages(), always tries to reclaim SGX_NR_TO_SCAN pages from the LRU of the given EPC cgroup, and only moves to its descendants when there's no enough reclaimable EPC pages to "scan" in its LRU. It should be enough for most cases. 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): 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. Alternatively, the current sgx_reclaim_pages() could be changed to return the actual "reclaimed" pages, but not "scanned" pages. However, the reclamation is a lengthy process, forcing a successful reclamation of predetermined number of pages may block the caller for too long. And that may not be acceptable in some synchronous contexts, e.g., in serving an ioctl(). With this building block in place, add synchronous reclamation support in sgx_cgroup_try_charge(): trigger a call to sgx_cgroup_reclaim_pages() if the cgroup reaches its limit and the caller allows synchronous reclaim as indicated by s newly added parameter. A later patch will add support for asynchronous reclamation reusing sgx_cgroup_reclaim_pages(). Note all reclaimable EPC pages are still tracked in the global LRU thus no per-cgroup reclamation is actually active at the moment. Per-cgroup tracking and reclamation will be turned on in the end after all necessary infrastructure is in place. Nit: "all necessary infrastructures are in place", or, "all necessary building blocks are in place". ? Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Signed-off-by: Kristen Carlson Accardi Co-developed-by: Haitao Huang Signed-off-by: Haitao Huang Tested-by: Jarkko Sakkinen --- Reviewed-by: Kai Huang More nitpickings below: [...] -static inline int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg) +static inline int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_reclaim reclaim) Let's still wrap the text on 80-character basis. I guess most people are more used to that. [...] - epc_page = list_first_entry_or_null(_global_lru.reclaimable, - struct sgx_epc_page, list); + epc_page = list_first_entry_or_null(>reclaimable, struct sgx_epc_page, list); Ditto.
[PATCH v12 08/14] x86/sgx: Add basic EPC reclamation flow for cgroup
From: Kristen Carlson Accardi Currently in the EPC page allocation, the kernel simply fails the allocation when the current EPC cgroup fails to charge due to its usage reaching limit. This is not ideal. When that happens, a better way is to reclaim EPC page(s) from the current EPC cgroup (and/or its descendants) to reduce its usage so the new allocation can succeed. Add the basic building blocks to support per-cgroup reclamation. Currently the kernel only has one place to reclaim EPC pages: the global EPC LRU list. To support the "per-cgroup" EPC reclaim, maintain an LRU list for each EPC cgroup, and introduce a "cgroup" variant function to reclaim EPC pages from a given EPC cgroup and its descendants. Currently the kernel does the global EPC reclaim in sgx_reclaim_page(). It always tries to reclaim EPC pages in batch of SGX_NR_TO_SCAN (16) pages. Specifically, it always "scans", or "isolates" SGX_NR_TO_SCAN pages from the global LRU, and then tries to reclaim these pages at once for better performance. Implement the "cgroup" variant EPC reclaim in a similar way, but keep the implementation simple: 1) change sgx_reclaim_pages() to take an LRU as input, and return the pages that are "scanned" and attempted for reclamation (but not necessarily reclaimed successfully); 2) loop the given EPC cgroup and its descendants and do the new sgx_reclaim_pages() until SGX_NR_TO_SCAN pages are "scanned". This implementation, encapsulated in sgx_cgroup_reclaim_pages(), always tries to reclaim SGX_NR_TO_SCAN pages from the LRU of the given EPC cgroup, and only moves to its descendants when there's no enough reclaimable EPC pages to "scan" in its LRU. It should be enough for most cases. 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): 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. Alternatively, the current sgx_reclaim_pages() could be changed to return the actual "reclaimed" pages, but not "scanned" pages. However, the reclamation is a lengthy process, forcing a successful reclamation of predetermined number of pages may block the caller for too long. And that may not be acceptable in some synchronous contexts, e.g., in serving an ioctl(). With this building block in place, add synchronous reclamation support in sgx_cgroup_try_charge(): trigger a call to sgx_cgroup_reclaim_pages() if the cgroup reaches its limit and the caller allows synchronous reclaim as indicated by s newly added parameter. A later patch will add support for asynchronous reclamation reusing sgx_cgroup_reclaim_pages(). Note all reclaimable EPC pages are still tracked in the global LRU thus no per-cgroup reclamation is actually active at the moment. Per-cgroup tracking and reclamation will be turned on in the end after all necessary infrastructure is in place. Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Signed-off-by: Kristen Carlson Accardi Co-developed-by: Haitao Huang Signed-off-by: Haitao Huang Tested-by: Jarkko Sakkinen --- V11: - Use commit message suggested by Kai - Remove "usage" comments for functions. (Kai) V10: - Simplify the signature by removing a pointer to nr_to_scan (Kai) - Return pages attempted instead of reclaimed as it is really what the cgroup caller needs to track progress. This further simplifies the design. - Merge patch for exposing sgx_reclaim_pages() with basic synchronous reclamation. (Kai) - Shorten names for EPC cgroup functions. (Jarkko) - Fix/add comments to justify the design (Kai) - Separate out a helper for for addressing single iteration of the loop in sgx_cgroup_try_charge(). (Jarkko) V9: - Add comments for static variables. (Jarkko) V8: - Use width of 80 characters in text paragraphs. (Jarkko) - Remove alignment for substructure variables. (Jarkko) 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. - Split this out from the big patch, #10 in V6. (Dave, Kai) --- arch/x86/kernel/cpu/sgx/epc_cgroup.c | 119 ++- arch/x86/kernel/cpu/sgx/epc_cgroup.h | 5 +- arch/x86/kernel/cpu/sgx/main.c | 45 ++ arch/x86/kernel/cpu/sgx/sgx.h| 1 + 4 files changed, 148 insertions(+), 22 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.c b/arch/x86/kernel/cpu/sgx/epc_cgroup.c index ff4d4a25dbe7..74d403d1e0d4 100644 ---