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Date: Mon, 25 Mar 2024 10:55:21 +0100
From: Joel Granados <j.granados@samsung.com>
To: Wen Yang <wenyang.linux@foxmail.com>
CC: "Eric W . Biederman" <ebiederm@xmission.com>, Luis Chamberlain
	<mcgrof@kernel.org>, Kees Cook <keescook@chromium.org>, Christian Brauner
	<brauner@kernel.org>, Iurii Zaikin <yzaikin@google.com>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/9] sysctl: support encoding values directly in the
 table entry
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On Fri, Mar 22, 2024 at 11:43:16PM +0800, Wen Yang wrote:
>=20
>=20
<--- snip --->
> > information that the NULL pointer gave you. This is effectively adding 2
> > bits per ctl_table element for all ctl_table types; event the ones that
> > do not need min max. So how much will we actually save with all this?
> > once you have added these 2 bits and removed the static variables from
> > the files that are not using the pointers? Is saving read only memory
> > the only reason for this? If that is the case, please add some
> > calculations of how much we save to see if it actually make sense. To
> > calculate the memory gains/losses you can use the bloat-o-meter script
> > under the scripts directory (something similar to what we did here
> > https://lore.kernel.org/all/20240314-jag-sysctl_remset_net-v1-0-aa26b44=
d29d9@samsung.com)
> >=20
> > I'll hold off on reviewing the other patches in this set until this is a
> > bit more clear.
> >=20
>=20
> Thank you for your comments.
>=20
> When we started this work, we had not yet seen Thomas's patch, so by=20
> borrowing the existing enum type=E2=80=98s field, we can achieve directly=
=20
> encoding values without increasing the size of the ctl_table.
>=20
> We really appreciate that you pointed out this issue. It will take some=
=20
> time for rework and the v3 will be sent out within a few weeks.
>=20
> In addition, the patch below is not related to "kill sysctl_vals". It is=
=20
> just a regular optimization and was sent over 10 days ago. We also hope=
=20
> to receive your kind advice:
>=20
> https://lkml.org/lkml/2024/3/8/871
>=20
> [RESEND PATCH v2] sysctl: move the extra1/2 boundary check of u8 to=20
> sysctl_check_table_array

Thx for pointing this out, I had missed it. On my todo list :)

>=20
> --
> Best wishes,
> Wen
>=20
>=20
> >> +	union {
> >> +		struct {
> >> +			void *extra1;
> >> +			void *extra2;
> >> +		};
> >> +		struct {
> >> +			long min;
> >> +			long max;
> >> +		};
> >> +	};
> >> +
> >>   	proc_handler *proc_handler;	/* Callback for text formatting */
> >>   	struct ctl_table_poll *poll;
> >> -	void *extra1;
> >> -	void *extra2;
> >>   } __randomize_layout;
> > ...
> >=20
> > Best
>=20

--=20

Joel Granados

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