linux-kernel - Re: [PATCH 00/13] mm: jit/text allocator

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Message-ID: <ZH0EseWI9F1n9yJx@moria.home.lan>
Date:   Sun, 4 Jun 2023 17:40:01 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Song Liu <song@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "David S. Miller" <davem@...emloft.net>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Helge Deller <deller@....de>,
        Huacai Chen <chenhuacai@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Russell King <linux@...linux.org.uk>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, bpf@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-modules@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev,
        netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org,
        Puranjay Mohan <puranjay12@...il.com>
Subject: Re: [PATCH 00/13] mm: jit/text allocator

On Sun, Jun 04, 2023 at 02:22:30PM -0700, Song Liu wrote:
> On Sun, Jun 4, 2023 at 11:02 AM Kent Overstreet
> <kent.overstreet@...ux.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 here.
> 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 jitalloc,
> 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?

Yeah, as long as that's the plan. Maybe one of you could tell us what
issues were preventing prog_pack from being used in the first place, it
might be relevant - this is the time to get the new allocator API right.