netdev - Re: [PATCH bpf 2/2] bpf: use vmalloc with VM_ALLOW_HUGE_VMAP for bpf_prog

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Date:   Sun, 10 Apr 2022 23:56:52 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     Christoph Hellwig <hch@...radead.org>, Song Liu <song@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>,
        "imbrenda@...ux.ibm.com" <imbrenda@...ux.ibm.com>
Subject: Re: [PATCH bpf 2/2] bpf: use vmalloc with VM_ALLOW_HUGE_VMAP for
 bpf_prog_pack

On Sun, Apr 10, 2022 at 01:34:50AM +0000, Song Liu wrote:
> OTOH, it is probably beneficial for the modules to use something 
> similar to bpf_prog_pack, i.e., put text from multiple modules to a 
> single huge page. Of course, this requires non-trivial work in both 
> mm code and module code.
> 
> Given that 1) modules cannot use huge pages yet, and 2) module may
> use differently (with sharing), I think adding module_alloc_large()
> doesn't add much value at the moment. So we can just keep this logic
> in BPF for now. 
> 
> Does this make sense?

I'm not intending to say modules should use the new helper.  But I'd much
prefer to keep all the MODULES_VADDR related bits self-contained in the
modules code and not splatter it over random other subsystems.