linux-kernel - Re: [PATCH] sched: make struct task

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Message-ID: <d8ad0be1-4ed7-df74-d415-2b1c9a44bac7@arm.com>
Date:   Tue, 3 Sep 2019 18:29:06 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Alexey Dobriyan <adobriyan@...il.com>, mingo@...hat.com,
        peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        linux-block@...r.kernel.org, dm-devel@...hat.com, axboe@...nel.dk,
        aarcange@...hat.com
Subject: Re: [PATCH] sched: make struct task_struct::state 32-bit

On 02/09/2019 22:05, Alexey Dobriyan wrote:
> 32-bit accesses are shorter than 64-bit accesses on x86_64.
> Nothing uses 64-bitness of ->state.
> 
> Space savings are ~2KB on F30 kernel config.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
>  arch/ia64/kernel/perfmon.c   |    4 ++--
>  block/blk-mq.c               |    2 +-
>  drivers/md/dm.c              |    4 ++--
>  fs/userfaultfd.c             |    2 +-
>  include/linux/sched.h        |    6 +++---
>  include/linux/sched/debug.h  |    2 +-
>  include/linux/sched/signal.h |    2 +-
>  kernel/freezer.c             |    2 +-
>  kernel/kthread.c             |    4 ++--
>  kernel/locking/mutex.c       |    6 +++---
>  kernel/locking/semaphore.c   |    2 +-
>  kernel/rcu/rcutorture.c      |    4 ++--
>  kernel/rcu/tree_stall.h      |    6 +++---
>  kernel/sched/core.c          |    8 ++++----
>  lib/syscall.c                |    2 +-
>  15 files changed, 28 insertions(+), 28 deletions(-)
> 

It looks like you missed a few places. There's a long prev_state in
sched/core.c::finish_task_switch() for instance.

I suppose that's where coccinelle oughta help but I'm really not fluent
in that. Is there a way to make it match p.state accesses with p task_struct?
And if so, can we make it change the type of the variable being read from
/ written to?

How did you come up with this changeset, did you pickaxe for some regexp?

[...]