linux-kernel - Re: [PATCH v7 09/10] memcg: enable accounting for tty-related objects

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Date:   Tue, 27 Jul 2021 08:54:31 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Vasily Averin <vvs@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     cgroups@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Roman Gushchin <guro@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 09/10] memcg: enable accounting for tty-related objects

On 27. 07. 21, 7:34, Vasily Averin wrote:
> At each login the user forces the kernel to create a new terminal and
> allocate up to ~1Kb memory for the tty-related structures.
> 
> By default it's allowed to create up to 4096 ptys with 1024 reserve for
> initial mount namespace only and the settings are controlled by host admin.
> 
> Though this default is not enough for hosters with thousands
> of containers per node. Host admin can be forced to increase it
> up to NR_UNIX98_PTY_MAX = 1<<20.
> 
> By default container is restricted by pty mount_opt.max = 1024,
> but admin inside container can change it via remount. As a result,
> one container can consume almost all allowed ptys
> and allocate up to 1Gb of unaccounted memory.
> 
> It is not enough per-se to trigger OOM on host, however anyway, it allows
> to significantly exceed the assigned memcg limit and leads to troubles
> on the over-committed node.
> 
> It makes sense to account for them to restrict the host's memory
> consumption from inside the memcg-limited container.
> 
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>   drivers/tty/tty_io.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 26debec..e787f6f 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1493,7 +1493,7 @@ void tty_save_termios(struct tty_struct *tty)
>   	/* Stash the termios data */
>   	tp = tty->driver->termios[idx];
>   	if (tp == NULL) {
> -		tp = kmalloc(sizeof(*tp), GFP_KERNEL);
> +		tp = kmalloc(sizeof(*tp), GFP_KERNEL_ACCOUNT);

termios are not saved for PTYs (TTY_DRIVER_RESET_TERMIOS). Am I missing 
something?

>   		if (tp == NULL)
>   			return;
>   		tty->driver->termios[idx] = tp;
> @@ -3119,7 +3119,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
>   {
>   	struct tty_struct *tty;
>   
> -	tty = kzalloc(sizeof(*tty), GFP_KERNEL);
> +	tty = kzalloc(sizeof(*tty), GFP_KERNEL_ACCOUNT);
>   	if (!tty)
>   		return NULL;
>   
> 

thanks,
-- 
js
suse labs