linux-kernel - Re: [PATCH v9 mm-new 03/11] mm: thp: add support for BPF based THP order selection

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Message-ID: <CAADnVQJtrJZOCWZKH498GBA8M0mYVztApk54mOEejs8Wr3nSiw@mail.gmail.com>
Date: Thu, 2 Oct 2025 19:18:33 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Yafang Shao <laoar.shao@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, ziy@...dia.com, 
	baolin.wang@...ux.alibaba.com, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Liam Howlett <Liam.Howlett@...cle.com>, npache@...hat.com, ryan.roberts@....com, 
	dev.jain@....com, Johannes Weiner <hannes@...xchg.org>, usamaarif642@...il.com, 
	gutierrez.asier@...wei-partners.com, Matthew Wilcox <willy@...radead.org>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Amery Hung <ameryhung@...il.com>, 
	David Rientjes <rientjes@...gle.com>, Jonathan Corbet <corbet@....net>, 21cnbao@...il.com, 
	Shakeel Butt <shakeel.butt@...ux.dev>, Tejun Heo <tj@...nel.org>, lance.yang@...ux.dev, 
	Randy Dunlap <rdunlap@...radead.org>, bpf <bpf@...r.kernel.org>, 
	linux-mm <linux-mm@...ck.org>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 mm-new 03/11] mm: thp: add support for BPF based THP
 order selection

On Mon, Sep 29, 2025 at 10:59 PM Yafang Shao <laoar.shao@...il.com> wrote:
>
> +unsigned long bpf_hook_thp_get_orders(struct vm_area_struct *vma,
> +                                     enum tva_type type,
> +                                     unsigned long orders)
> +{
> +       thp_order_fn_t *bpf_hook_thp_get_order;
> +       int bpf_order;
> +
> +       /* No BPF program is attached */
> +       if (!test_bit(TRANSPARENT_HUGEPAGE_BPF_ATTACHED,
> +                     &transparent_hugepage_flags))
> +               return orders;
> +
> +       rcu_read_lock();
> +       bpf_hook_thp_get_order = rcu_dereference(bpf_thp.thp_get_order);
> +       if (WARN_ON_ONCE(!bpf_hook_thp_get_order))
> +               goto out;
> +
> +       bpf_order = bpf_hook_thp_get_order(vma, type, orders);
> +       orders &= BIT(bpf_order);
> +
> +out:
> +       rcu_read_unlock();
> +       return orders;
> +}

I thought I explained it earlier.
Nack to a single global prog approach.

The logic must accommodate multiple programs per-container
or any other way from the beginning.
If cgroup based scoping doesn't fit use per process tree scoping.