Re: [RFC PATCH V1 1/1] sched/numa: Enhance vma scanning logic

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On 1/17/2023 4:44 PM, David Hildenbrand wrote:
On 16.01.23 03:25, Raghavendra K T wrote:
  During the Numa scanning make sure only relevant vmas of the
tasks are scanned.

Logic:
1) For the first two time allow unconditional scanning of vmas
2) Store recent 4 unique tasks (last 8bits of PIDs) accessed the vma.
   False negetives in case of collison should be fine here.
3) If more than 4 pids exist assume task indeed accessed vma to
  to avoid false negetives

Co-developed-by: Bharata B Rao <bharata@xxxxxxx>
(initial patch to store pid information)

Suggested-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Bharata B Rao <bharata@xxxxxxx>
Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxx>
---
  include/linux/mm_types.h |  2 ++
  kernel/sched/fair.c      | 32 ++++++++++++++++++++++++++++++++
  mm/memory.c              | 21 +++++++++++++++++++++
  3 files changed, 55 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 500e536796ca..07feae37b8e6 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -506,6 +506,8 @@ struct vm_area_struct {
      struct mempolicy *vm_policy;    /* NUMA policy for the VMA */
  #endif
      struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
+    unsigned int accessing_pids;
+    int next_pid_slot;
  } __randomize_layout;

What immediately jumps at me is the unconditional grow of a VMA by 8 bytes. A process with 64k mappings consumes 512 KiB more of memory, possibly completely unnecessarily.

This at least needs to be fenced by CONFIG_NUMA_BALANCING.


Thanks for the review David. Good point..  I do agree. I see I will have
to fence further in memory.c only since fair.c is already taken care.




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