Re: [PATCH bpf-next v7 1/4] bpf: Add a sleepable page allocator for map memory

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Thu, Sep 17, 2026 at 09:55 AM Jiayuan Chen <jiayuan.chen@linux.dev> wrote:
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index e80963971f680..345fe4c2e6422 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2786,6 +2786,7 @@ struct bpf_prog *bpf_prog_get_curr_or_next(u32 *id);
>
>  int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
>  			unsigned long nr_pages, struct page **page_array);
> +struct page *bpf_map_alloc_page_sleepable(const struct bpf_map *map);

[...]

> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index c7bc9ba9b331f..abd0f67c68d97 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c

[...]

> @@ -636,6 +635,27 @@ int bpf_map_alloc_pages(const struct bpf_map *map, int nid,
>  	return ret;
>  }
>
> +/*
> + * Allocate a page for map memory with the blocking allocator so it can
> + * reclaim. __GFP_RETRY_MAYFAIL keeps it from invoking the OOM killer: the
> + * page is charged to
 the map's memcg, which need not be the caller's, so
> + * an OOM there could kill unrelated tasks in the map's cgroup while a
> + * foreign caller could never be its victim.
> + *
> + * bpf_map_alloc_pages() serves arbitrary BPF program context and stays
> + * reentrancy-safe by falling back to the non-blocking allocator. This
> + * helper always blocks, so a sleepable context alone is not enough: the
> + * caller must guarantee it is not already inside the page allocator or
> + * reclaim, where blocking here would reenter mm and deadlock. The only
> + * user is arena_vm_fault(), a userspace page fault in task context.
> + */
> +struct page *bpf_map_alloc_page_sleepable(const struct bpf_map *map)
> +{
> +	might_sleep();
> +	return alloc_pages_node(map->numa_node,
> +				BPF_PAGE_GFP | __GFP_RETRY_MAYFAIL, 0);
> +}

Don't see the point in #define BPF_PAGE_GFP

Just call
  alloc_pages_node(map->numa_node, GFP_KERNEL | __GFP_ZERO |
		   __GFP_ACCOUNT | __GFP_NOWARN 
| __GFP_RETRY_MAYFAIL, 0);

with a one line comment why RETRY_MAYFAIL, 
drop this patch and fold mayfail+comment into patch 2.

pw-bot: cr