From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vasily Averin Subject: Re: [PATCH v7 09/10] memcg: enable accounting for tty-related objects Date: Tue, 27 Jul 2021 11:02:31 +0300 Message-ID: References: <6f21a0e0-bd36-b6be-1ffa-0dc86c06c470@virtuozzo.com> <1eef95fe-6172-796e-edd1-095545da6e74@kernel.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=Content-Type:MIME-Version:Date:Message-ID:From: Subject; bh=W5ZkylOW4aorWqYoZgdy9OUAHDEpy8dU4QmNRvPVlOs=; b=Yj12nar4kB+x0tcn9 97g0z8UReUWtZBd8M7TK4t+EblgWkMtLRxzEGpJndlo5lJBaTOwX6Ie72E40Rk0K8jA0cK/uuB36K LvHZgC3Qjsg3GnIS9NTYCQTgU7QuHIYd0xtpICYl/ho2irAdnFnf2UYH2M9kP6NIg+CLeRnurfSpY =; In-Reply-To: <1eef95fe-6172-796e-edd1-095545da6e74-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Content-Language: en-US List-ID: Content-Type: text/plain; charset="utf-8" To: Jiri Slaby Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Greg Kroah-Hartman , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On 7/27/21 9:54 AM, Jiri Slaby wrote: > 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 >> Acked-by: Greg Kroah-Hartman >> --- >>   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? No, you are right, I've missed this. Typical terminals inside containers use TTY_DRIVER_RESET_TERMIOS flag and therefore do not save termios. So its accounting have near-to-zero impact in real life. I'll prepare fixup to drop GFP_KERNEL_ACCOUNT here. Thank you very much, Vasily Averin >>           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,