[bpf-next,v4,0/6] bpf, mm: Introduce try_alloc_pages()

Message

Alexei Starovoitov Jan. 14, 2025, 2:19 a.m. UTC

From: Alexei Starovoitov <[e-mail]>

Hi All,

The main motivation is to make alloc page and slab reentrant and
remove bpf_mem_alloc.

v3->v4:
Addressed feedback from Michal and Shakeel:
- GFP_TRYLOCK flag is gone. gfpflags_allow_spinning() is used instead.
- Improved comments and commit logs.

v3:
https://lore.kernel.org/bpf/[e-mail]/

v2->v3:
To address the issues spotted by Sebastian, Vlastimil, Steven:
- Made GFP_TRYLOCK internal to mm/internal.h
  try_alloc_pages() and free_pages_nolock() are the only interfaces.
- Since spin_trylock() is not safe in RT from hard IRQ and NMI
  disable such usage in lock_trylock and in try_alloc_pages().
  In such case free_pages_nolock() falls back to llist right away.
- Process trylock_free_pages llist when preemptible.
- Check for things like unaccepted memory and order <= 3 early.
- Don't call into __alloc_pages_slowpath() at all.
- Inspired by Vlastimil's struct local_tryirq_lock adopted it in
  local_lock_t. Extra 4 bytes in !RT in local_lock_t shouldn't
  affect any of the current local_lock_t users. This is patch 3.
- Tested with bpf selftests in RT and !RT and realized how much
  more work is necessary on bpf side to play nice with RT.
  The urgency of this work got higher. The alternative is to
  convert bpf bits left and right to bpf_mem_alloc.

v2:
https://lore.kernel.org/bpf/[e-mail]/

v1->v2:
- fixed buggy try_alloc_pages_noprof() in PREEMPT_RT. Thanks Peter.
- optimize all paths by doing spin_trylock_irqsave() first
  and only then check for gfp_flags & __GFP_TRYLOCK.
  Then spin_lock_irqsave() if it's a regular mode.
  So new gfp flag will not add performance overhead.
- patches 2-5 are new. They introduce lockless and/or trylock free_pages_nolock()
  and memcg support. So it's in usable shape for bpf in patch 6.

v1:
https://lore.kernel.org/bpf/[e-mail]/

Alexei Starovoitov (6):
  mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation
  mm, bpf: Introduce free_pages_nolock()
  locking/local_lock: Introduce local_trylock_irqsave()
  memcg: Use trylock to access memcg stock_lock.
  mm, bpf: Use memcg in try_alloc_pages().
  bpf: Use try_alloc_pages() to allocate pages for bpf needs.

 include/linux/gfp.h                 |  23 ++++
 include/linux/local_lock.h          |   9 ++
 include/linux/local_lock_internal.h |  76 +++++++++++--
 include/linux/mm_types.h            |   4 +
 include/linux/mmzone.h              |   3 +
 kernel/bpf/syscall.c                |   4 +-
 mm/internal.h                       |   1 +
 mm/memcontrol.c                     |  24 +++-
 mm/page_alloc.c                     | 170 ++++++++++++++++++++++++++--
 9 files changed, 290 insertions(+), 24 deletions(-)