Re: [PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator.

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

On Fri, 19 Aug 2022 at 23:42, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> Introduce any context BPF specific memory allocator.
>
> Tracing BPF programs can attach to kprobe and fentry. Hence they
> run in unknown context where calling plain kmalloc() might not be safe.
> Front-end kmalloc() with per-cpu cache of free elements.
> Refill this cache asynchronously from irq_work.
>
> Major achievements enabled by bpf_mem_alloc:
> - Dynamically allocated hash maps used to be 10 times slower than fully preallocated.
>   With bpf_mem_alloc and subsequent optimizations the speed of dynamic maps is equal to full prealloc.
> - Tracing bpf programs can use dynamically allocated hash maps.
>   Potentially saving lots of memory. Typical hash map is sparsely populated.
> - Sleepable bpf programs can used dynamically allocated hash maps.
>

From my side, for the whole series:
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>


> v2->v3:
> - Rewrote the free_list algorithm based on discussions with Kumar. Patch 1.
> - Allowed sleepable bpf progs use dynamically allocated maps. Patches 13 and 14.
> - Added sysctl to force bpf_mem_alloc in hash map even if pre-alloc is
>   requested to reduce memory consumption. Patch 15.
> - Fix: zero-fill percpu allocation
> - Single rcu_barrier at the end instead of each cpu during bpf_mem_alloc destruction
>
> v2 thread:
> https://lore.kernel.org/bpf/20220817210419.95560-1-alexei.starovoitov@gmail.com/
>
> v1->v2:
> - Moved unsafe direct call_rcu() from hash map into safe place inside bpf_mem_alloc. Patches 7 and 9.
> - Optimized atomic_inc/dec in hash map with percpu_counter. Patch 6.
> - Tuned watermarks per allocation size. Patch 8
> - Adopted this approach to per-cpu allocation. Patch 10.
> - Fully converted hash map to bpf_mem_alloc. Patch 11.
> - Removed tracing prog restriction on map types. Combination of all patches and final patch 12.
>
> v1 thread:
> https://lore.kernel.org/bpf/20220623003230.37497-1-alexei.starovoitov@gmail.com/
>
> LWN article:
> https://lwn.net/Articles/899274/
>
> Future work:
> - expose bpf_mem_alloc as uapi FD to be used in dynptr_alloc, kptr_alloc
> - convert lru map to bpf_mem_alloc
>
> Alexei Starovoitov (15):
>   bpf: Introduce any context BPF specific memory allocator.
>   bpf: Convert hash map to bpf_mem_alloc.
>   selftests/bpf: Improve test coverage of test_maps
>   samples/bpf: Reduce syscall overhead in map_perf_test.
>   bpf: Relax the requirement to use preallocated hash maps in tracing
>     progs.
>   bpf: Optimize element count in non-preallocated hash map.
>   bpf: Optimize call_rcu in non-preallocated hash map.
>   bpf: Adjust low/high watermarks in bpf_mem_cache
>   bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.
>   bpf: Add percpu allocation support to bpf_mem_alloc.
>   bpf: Convert percpu hash map to per-cpu bpf_mem_alloc.
>   bpf: Remove tracing program restriction on map types
>   bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.
>   bpf: Remove prealloc-only restriction for sleepable bpf programs.
>   bpf: Introduce sysctl kernel.bpf_force_dyn_alloc.
>
>  include/linux/bpf_mem_alloc.h             |  26 +
>  include/linux/filter.h                    |   2 +
>  kernel/bpf/Makefile                       |   2 +-
>  kernel/bpf/core.c                         |   2 +
>  kernel/bpf/hashtab.c                      | 132 +++--
>  kernel/bpf/memalloc.c                     | 601 ++++++++++++++++++++++
>  kernel/bpf/syscall.c                      |  14 +-
>  kernel/bpf/verifier.c                     |  52 --
>  samples/bpf/map_perf_test_kern.c          |  44 +-
>  samples/bpf/map_perf_test_user.c          |   2 +-
>  tools/testing/selftests/bpf/progs/timer.c |  11 -
>  tools/testing/selftests/bpf/test_maps.c   |  38 +-
>  12 files changed, 795 insertions(+), 131 deletions(-)
>  create mode 100644 include/linux/bpf_mem_alloc.h
>  create mode 100644 kernel/bpf/memalloc.c
>
> --
> 2.30.2
>