linux-kernel - Re: [PATCH] oom_reaper: switch to struct list

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Message-ID: <20170215080847.GA28090@gmail.com>
Date:   Wed, 15 Feb 2017 09:08:47 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Aleksa Sarai <asarai@...e.de>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, cyphar@...har.com
Subject: Re: [PATCH] oom_reaper: switch to struct list_head for reap queue


* Aleksa Sarai <asarai@...e.de> wrote:

> >>Rather than implementing an open addressing linked list structure
> >>ourselves, use the standard list_head structure to improve consistency
> >>with the rest of the kernel and reduce confusion.
> >>
> >>Cc: Michal Hocko <mhocko@...e.com>
> >>Cc: Oleg Nesterov <oleg@...hat.com>
> >>Signed-off-by: Aleksa Sarai <asarai@...e.de>
> >>---
> >> include/linux/sched.h |  6 +++++-
> >> kernel/fork.c         |  4 ++++
> >> mm/oom_kill.c         | 24 +++++++++++++-----------
> >> 3 files changed, 22 insertions(+), 12 deletions(-)
> >>
> >>diff --git a/include/linux/sched.h b/include/linux/sched.h
> >>index e93594b88130..d8bcd0f8c5fe 100644
> >>--- a/include/linux/sched.h
> >>+++ b/include/linux/sched.h
> >>@@ -1960,7 +1960,11 @@ struct task_struct {
> >> #endif
> >> 	int pagefault_disabled;
> >> #ifdef CONFIG_MMU
> >>-	struct task_struct *oom_reaper_list;
> >>+	/*
> >>+	 * List of threads that have to be reaped by OOM (rooted at
> >>+	 * &oom_reaper_list in mm/oom_kill.c).
> >>+	 */
> >>+	struct list_head oom_reaper_list;
> >
> >This is an extra pointer to task_struct and more lines of code to
> >accomplish the same thing. Why would we want to do that?
> 
> I don't think it's more "actual" lines of code (I think the wrapping is
> inflating the line number count), but switching it means that it's more in
> line with other queues in the kernel (it took me a bit to figure out what
> was going on with oom_reaper_list beforehand).

It's still an extra pointer and extra generated code to do the same thing - a clear step backwards.

Thanks,

	Ingo