This is follow-up to the LSF/MM proposal [1]. Please provide your thoughts and comments about dynamic kernel stacks feature. This is a WIP has not been tested beside booting on some machines, and running LKDTM thread exhaust tests. The series also lacks selftests, and documentations. This feature allows to grow kernel stack dynamically, from 4KiB and up to the THREAD_SIZE. The intend is to save memory on fleet machines. From the initial experiments it shows to save on average 70-75% of the kernel stack memory. The average depth of a kernel thread depends on the workload, profiling, virtualization, compiler optimizations, and driver implementations. However, the table below shows the amount of kernel stack memory before vs. after on idling freshly booted machines: CPU #Cores #Stacks BASE(kb) Dynamic(kb) Saving AMD Genoa 384 5786 92576 23388 74.74% Intel Skylake 112 3182 50912 12860 74.74% AMD Rome 128 3401 54416 14784 72.83% AMD Rome 256 4908 78528 20876 73.42% Intel Haswell 72 2644 42304 10624 74.89% Some workloads with that have millions of threads would can benefit significantly from this feature. [1] https://lore.kernel.org/all/CA+CK2bBYt9RAVqASB2eLyRQxYT5aiL0fGhUu3TumQCyJCNTWvw@xxxxxxxxxxxxxx Pasha Tatashin (14): task_stack.h: remove obsolete __HAVE_ARCH_KSTACK_END check fork: Clean-up ifdef logic around stack allocation fork: Clean-up naming of vm_strack/vm_struct variables in vmap stacks code fork: Remove assumption that vm_area->nr_pages equals to THREAD_SIZE fork: check charging success before zeroing stack fork: zero vmap stack using clear_page() instead of memset() fork: use the first page in stack to store vm_stack in cached_stacks fork: separate vmap stack alloction and free calls mm/vmalloc: Add a get_vm_area_node() and vmap_pages_range_noflush() public functions fork: Dynamic Kernel Stacks x86: add support for Dynamic Kernel Stacks task_stack.h: Clean-up stack_not_used() implementation task_stack.h: Add stack_not_used() support for dynamic stack fork: Dynamic Kernel Stack accounting arch/Kconfig | 33 +++ arch/x86/Kconfig | 1 + arch/x86/kernel/traps.c | 3 + arch/x86/mm/fault.c | 3 + include/linux/mmzone.h | 3 + include/linux/sched.h | 2 +- include/linux/sched/task_stack.h | 94 ++++++-- include/linux/vmalloc.h | 15 ++ kernel/fork.c | 388 ++++++++++++++++++++++++++----- kernel/sched/core.c | 1 + mm/internal.h | 9 - mm/vmalloc.c | 24 ++ mm/vmstat.c | 3 + 13 files changed, 487 insertions(+), 92 deletions(-) -- 2.44.0.278.ge034bb2e1d-goog
