linux-kernel - Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <mvpuegbh5gttbflarqua5wa7ar42zy5d6hxqf7me6nxwk7yibm@bxwxkt4h5fx5>
Date: Wed, 19 Mar 2025 11:20:26 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Greg Thelen <gthelen@...gle.com>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Yosry Ahmed <yosryahmed@...gle.com>, cgroups@...r.kernel.org, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu)

Hello.

On Wed, Mar 19, 2025 at 12:13:30AM -0700, Greg Thelen <gthelen@...gle.com> wrote:
> cgroup_rstat_flush_locked() grabs the irq safe cgroup_rstat_lock while
> iterating all possible cpus. It only drops the lock if there is
> scheduler or spin lock contention. If neither, then interrupts can be
> disabled for a long time. On large machines this can disable interrupts
> for a long enough time to drop network packets. On 400+ CPU machines
> I've seen interrupt disabled for over 40 msec.

This is peanuts, watchdog_thresh defaults to 10000 msec.
(Tongue-in-cheek, to put that threshold into relation but I see the
problem.)


> The mode of memory.stat access latency after grouping by of 2 buckets:
                                                        power

> - without memory hogs: 64 usec => 16 usec
> -    with memory hogs: 64 usec =>  8 usec
> The memory.stat latency improves.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Greg Thelen <gthelen@...gle.com>
> Tested-by: Greg Thelen <gthelen@...gle.com>
> ---
>  kernel/cgroup/rstat.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)

FTR, the lock may end up split per-subsys [1] but this would still make
sense for memcg's one. (I wonder if Tejun would consider it small enough
then to avoid interrupt disabling. Then this could be converted to more
widely used cond_resched_lock().)

[1] https://lore.kernel.org/r/20250227215543.49928-4-inwardvessel@gmail.com/

But all in all, thanks for this and

Acked-by: Michal Koutný <mkoutny@...e.com>

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)