diff options
| author | Alexei Starovoitov <ast@kernel.org> | 2025-02-21 18:44:23 -0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2025-02-27 09:32:27 -0800 |
| commit | 97769a53f117e2f33864c587d85992ee35194ecf (patch) | |
| tree | 257ef0eda79af4065d8a86845b948b7c853d8287 /lib/stackdepot.c | |
| parent | 0aaddfb06882504dded9cde57f91035ab9403b82 (diff) | |
mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation
Tracing BPF programs execute from tracepoints and kprobes where
running context is unknown, but they need to request additional
memory. The prior workarounds were using pre-allocated memory and
BPF specific freelists to satisfy such allocation requests.
Instead, introduce gfpflags_allow_spinning() condition that signals
to the allocator that running context is unknown.
Then rely on percpu free list of pages to allocate a page.
try_alloc_pages() -> get_page_from_freelist() -> rmqueue() ->
rmqueue_pcplist() will spin_trylock to grab the page from percpu
free list. If it fails (due to re-entrancy or list being empty)
then rmqueue_bulk()/rmqueue_buddy() will attempt to
spin_trylock zone->lock and grab the page from there.
spin_trylock() is not safe in PREEMPT_RT when in NMI or in hard IRQ.
Bailout early in such case.
The support for gfpflags_allow_spinning() mode for free_page and memcg
comes in the next patches.
This is a first step towards supporting BPF requirements in SLUB
and getting rid of bpf_mem_alloc.
That goal was discussed at LSFMM: https://lwn.net/Articles/974138/
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20250222024427.30294-3-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'lib/stackdepot.c')
| -rw-r--r-- | lib/stackdepot.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 245d5b416699..377194969e61 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -591,7 +591,8 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, depot_stack_handle_t handle = 0; struct page *page = NULL; void *prealloc = NULL; - bool can_alloc = depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC; + bool allow_spin = gfpflags_allow_spinning(alloc_flags); + bool can_alloc = (depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC) && allow_spin; unsigned long flags; u32 hash; @@ -630,7 +631,7 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, prealloc = page_address(page); } - if (in_nmi()) { + if (in_nmi() || !allow_spin) { /* We can never allocate in NMI context. */ WARN_ON_ONCE(can_alloc); /* Best effort; bail if we fail to take the lock. */ |