linux-kernel - Re: [patch] mm, oom: add comment for why oom

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Message-ID: <009801d11846$7eb2f610$7c18e230$@alibaba-inc.com>
Date:	Fri, 06 Nov 2015 11:52:01 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"David Rientjes" <rientjes@...gle.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Michal Hocko" <mhocko@...nel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <Hongjie.Fang@...eadtrum.com>,
	"'Eric W. Biederman'" <ebiederm@...ssion.com>
Subject: Re: [patch] mm, oom: add comment for why oom_adj exists

> 
> /proc/pid/oom_adj exists solely to avoid breaking existing userspace
> binaries that write to the tunable.
> 
> Add a comment in the only possible location within the kernel tree to
> describe the situation and motivation for keeping it around.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---

Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>

>  fs/proc/base.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1032,6 +1032,16 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
>  	return simple_read_from_buffer(buf, count, ppos, buffer, len);
>  }
> 
> +/*
> + * /proc/pid/oom_adj exists solely for backwards compatibility with previous
> + * kernels.  The effective policy is defined by oom_score_adj, which has a
> + * different scale: oom_adj grew exponentially and oom_score_adj grows linearly.
> + * Values written to oom_adj are simply mapped linearly to oom_score_adj.
> + * Processes that become oom disabled via oom_adj will still be oom disabled
> + * with this implementation.
> + *
> + * oom_adj cannot be removed since existing userspace binaries use it.
> + */
>  static ssize_t oom_adj_write(struct file *file, const char __user *buf,
>  			     size_t count, loff_t *ppos)
>  {
> --

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