linux-kernel - Re: [PATCH 7/7] block, drivers: make lots of attribute

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Date:   Mon, 9 Oct 2023 19:40:00 +0200
From:   Max Kellermann <max.kellermann@...os.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rodolfo Giometti <giometti@...eenne.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Mark Fasheh <mark@...heh.com>,
        Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ceph-devel@...r.kernel.org, linux-input@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-rtc@...r.kernel.org,
        linux-serial@...r.kernel.org, ocfs2-devel@...ts.linux.dev,
        linux-mm@...ck.org
Subject: Re: [PATCH 7/7] block, drivers: make lots of attribute_group globals const

On Mon, Oct 9, 2023 at 7:30 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Oct 09, 2023 at 06:57:40PM +0200, Max Kellermann wrote:
> > This moves those variables to the ".rodata" section which reduces the
> > kernel size a bit and protects the variables by putting them on
> > read-only pages at runtime.
>
> The kernel size should still be the same overall, you are just moving
> pointers from one section to another, right?
>
> If not, what are the numbers, show them please.

Before this patch series:

   text       data        bss        dec        hex    filename
10645342    6836166    12476420    29957928    1c91f28    vmlinux

After:

   text       data        bss        dec        hex    filename
10645342    6835398    12476420    29957160    1c91c28    vmlinux

(Config attached if you wish to reproduce. I'm using stock GCC from
Debian Bookworm.)

It's only a few hundred bytes, and I havn't really dug deep enough to
explain to you why this is - my goal was (semantic) const-correctness
and .rodata protection, but those numbers are a side effect that
exists.


> But step back, are you SURE you can make these attribute group pointers
> const?  They are modified by some subsystems by adding or removing items
> from the lists, so why does the core need to change for that?

Some few do modify them, but they do not modify those pointers; they
allocate a new one (the 3 I sbumitted a patch for) or they modify
global variables (arch/pmu) which I'm not going to make "const". But
most globals can indeed be made "const".

Download attachment ".config" of type "application/octet-stream" (81166 bytes)