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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Song Liu <songliubraving@fb.com>
Cc: Song Liu <song@kernel.org>, bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Kernel Team <Kernel-team@fb.com>,
	Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>
Subject: Re: [PATCH v5 bpf-next 7/7] bpf, x86_64: use bpf_prog_pack allocator
Date: Fri, 21 Jan 2022 10:29:55 -0800	[thread overview]
Message-ID: <CAADnVQLWj6cVE=OEqNfSBcAzFJDHPF8sPfqGfaCknV+Q=1HOmQ@mail.gmail.com> (raw)
In-Reply-To: <F72EEF0D-4F61-4AE1-B2A1-D16A5DBCCC37@fb.com>

On Fri, Jan 21, 2022 at 9:53 AM Song Liu <songliubraving@fb.com> wrote:
> >
> > the header->size could be just below 2MB.
> > I don't think kzalloc() can handle that.
>
> Technically, kzalloc can handle 2MB allocation via:
>   kzalloc() => kmalloc() => kmalloc_large() => kmalloc_order()
>
> But this would fail when the memory is fragmented. I guess we should use
> kvmalloc() instead?

Contiguous 2MB allocation?

> >
> >> +                               if (!tmp_header) {
> >> +                                       bpf_jit_binary_free_pack(header);
> >> +                                       header = NULL;
> >> +                                       prog = orig_prog;
> >> +                                       goto out_addrs;
> >> +                               }
> >> +                               tmp_header->size = header->size;
> >> +                               tmp_image = (void *)tmp_header + ((void *)image - (void *)header);
> >
> > Why is 'tmp_image' needed at all?
> > The above math can be done where necessary.
>
> We pass both image and tmp_image to do_jit(), as it needs both of them.
> I think maintaining a tmp_image variable makes the logic cleaner. We can
> remove it from x64_jit_data, I guess.

I'd remove from x64_jit_data. The recompute is cheap.

Speaking of tmp_header name... would be great to come up
with something more descriptive.
Here both tmp_header/tmp_image and header/image are used at the same time.
My initial confusion with the patch was due to the name 'tmp'.
The "tmp" prefix implies that the tmp_image will be used first
and then it will become an image.
But it's not the case.
Maybe call it 'rw_header' and add a comment that 'header/image'
are not writeable directly ?
Or call it 'poke_header' ?
Other ideas?

  reply	other threads:[~2022-01-21 18:30 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-20 19:12 [PATCH v5 bpf-next 0/7] bpf_prog_pack allocator Song Liu
2022-01-20 19:12 ` [PATCH v5 bpf-next 1/7] x86/Kconfig: select HAVE_ARCH_HUGE_VMALLOC with HAVE_ARCH_HUGE_VMAP Song Liu
2022-01-20 19:13 ` [PATCH v5 bpf-next 2/7] bpf: use bytes instead of pages for bpf_jit_[charge|uncharge]_modmem Song Liu
2022-01-20 19:13 ` [PATCH v5 bpf-next 3/7] bpf: use size instead of pages in bpf_binary_header Song Liu
2022-01-20 19:13 ` [PATCH v5 bpf-next 4/7] bpf: add a pointer of bpf_binary_header to bpf_prog Song Liu
2022-01-20 19:13 ` [PATCH v5 bpf-next 5/7] x86/alternative: introduce text_poke_copy Song Liu
2022-01-21  9:52   ` Peter Zijlstra
2022-01-20 19:13 ` [PATCH v5 bpf-next 6/7] bpf: introduce bpf_prog_pack allocator Song Liu
2022-01-20 19:13 ` [PATCH v5 bpf-next 7/7] bpf, x86_64: use " Song Liu
2022-01-21  4:59   ` Alexei Starovoitov
2022-01-21 17:53     ` Song Liu
2022-01-21 18:29       ` Alexei Starovoitov [this message]
2022-01-21 18:56         ` Song Liu
2022-01-21  1:06 ` [PATCH v5 bpf-next 0/7] " Song Liu

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