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From:   Song Liu <song@kernel.org>
Date:   Sun, 4 Jun 2023 14:22:30 -0700
Message-ID: <CAPhsuW7iEDa44jxc_7Cj4KnVhtct-UTO2JtVK-U7o2ynn2iX8Q@mail.gmail.com>
Subject: Re: [PATCH 00/13] mm: jit/text allocator
To:     Kent Overstreet <kent.overstreet@linux.dev>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Mike Rapoport <rppt@kernel.org>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        "David S. Miller" <davem@davemloft.net>,
        Dinh Nguyen <dinguyen@kernel.org>,
        Heiko Carstens <hca@linux.ibm.com>,
        Helge Deller <deller@gmx.de>,
        Huacai Chen <chenhuacai@kernel.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Russell King <linux@armlinux.org.uk>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>, bpf@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
        linux-mm@kvack.org, linux-modules@vger.kernel.org,
        linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org,
        linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev,
        netdev@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org,
        Puranjay Mohan <puranjay12@gmail.com>
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On Sun, Jun 4, 2023 at 11:02=E2=80=AFAM Kent Overstreet
<kent.overstreet@linux.dev> wrote:
>
> On Fri, Jun 02, 2023 at 11:20:58AM -0700, Song Liu wrote:
> > IIUC, arm64 uses VMALLOC address space for BPF programs. The reason
> > is each BPF program uses at least 64kB (one page) out of the 128MB
> > address space. Puranjay Mohan (CC'ed) is working on enabling
> > bpf_prog_pack for arm64. Once this work is done, multiple BPF programs
> > will be able to share a page. Will this improvement remove the need to
> > specify a different address range for BPF programs?
>
> Can we please stop working on BPF specific sub page allocation and focus
> on doing this in mm/? This never should have been in BPF in the first
> place.

That work is mostly independent of the allocator work we are discussing her=
e.
The goal Puranjay's work is to enable the arm64 BPF JIT engine to use a
ROX allocator. The allocator could be the bpf_prog_pack allocator, or jital=
loc,
or module_alloc_type. Puranjay is using bpf_prog_alloc for now. But once
jitalloc or module_alloc_type (either one) is merged, we will migrate BPF
JIT engines (x86_64 and arm64) to the new allocator and then tear down
bpf_prog_pack.

Does this make sense?

Thanks,
Song