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From:   Song Liu <songliubraving@fb.com>
To:     KP Singh <kpsingh@kernel.org>
CC:     bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
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        Kernel Team <Kernel-team@fb.com>,
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Subject: Re: [PATCH bpf-next 1/4] bpf: enable task local storage for tracing
 programs
Thread-Topic: [PATCH bpf-next 1/4] bpf: enable task local storage for tracing
 programs
Thread-Index: AQHW5hbxN1bu8adE10+5MJhm5YS4VaoiOPkAgADahAA=
Date:   Mon, 11 Jan 2021 23:16:48 +0000
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> On Jan 11, 2021, at 2:14 AM, KP Singh <kpsingh@kernel.org> wrote:
>=20
> On Sat, Jan 9, 2021 at 12:35 AM Song Liu <songliubraving@fb.com> wrote:
>>=20
>> To access per-task data, BPF program typically creates a hash table with
>> pid as the key. This is not ideal because:
>> 1. The use need to estimate requires size of the hash table, with may be
>>    inaccurate;
>> 2. Big hash tables are slow;
>> 3. To clean up the data properly during task terminations, the user need
>>    to write code.
>>=20
>> Task local storage overcomes these issues and becomes a better option fo=
r
>> these per-task data. Task local storage is only available to BPF_LSM. No=
w
>> enable it for tracing programs.
>=20
> Also mention here that you change the pointer from being a security blob =
to a
> dedicated member in the task struct. I assume this is because you want to
> use it without CONFIG_BPF_LSM?

Yes, exactly. I will add this to the commit log.=20

>=20
>>=20
>=20
> Can you also mention the reasons for changing the
> raw_spin_lock_bh to raw_spin_lock_irqsave in the commit log?

This is because we will use these in irq context. I will add this to the=20
commit log.=20

Thanks,
Song