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bh=hU2mOFIakYu1JXvoaJZnS0pZd0tIlcvrypVKAXkNPt8=; b=0MeWC9VixBL+yIvcu/2Vlj+rC6XYBt0Lwwuj3lI+T3JWTk7UbRlU6/M9YpEreOhCvWu2Qs B88oLp/ncbGh3sUCtOPSFA/rk2AgtwtYIlEnGFFACtfQaCK2ZyZ52kjwggqe3hdfec4gjY 5hZh3sm7VvJylzBTo0G3yBviNVhGU1QBdUcmvlM7oo22hKZzut5vZBdUHIc1MFoqvVhUVV s7XDBVITq0Es3ChLniEuXjqIAn/m90t6UMj/LbsZz0cxH+aSLsaRKUxpya5OzxYBEEcjGx BTbdld+hUlBa4WNM4q8VP23PBdjCOQpZrBkWDV8v1VExSWa1ZS+TkuDN7fJUJw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1746435983; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hU2mOFIakYu1JXvoaJZnS0pZd0tIlcvrypVKAXkNPt8=; b=ZzjkqVyJrEYAyTAbEVRah1Hmfig2TmjA9h3qEpX0F3TlWJQjVp6+a5ySJH8PjLF0hAfJyy 34v9hcGVh2sJizCA== From: Sebastian Andrzej Siewior To: Shakeel Butt Cc: Alexei Starovoitov , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Alexei Starovoitov , linux-mm , "open list:CONTROL GROUP (CGROUP)" , bpf , LKML , Meta kernel team , Vlastimil Babka Subject: Re: [PATCH v2 3/3] memcg: no irq disable for memcg stock lock Message-ID: <20250505090617.Q6tHb1NH@linutronix.de> References: <20250502001742.3087558-1-shakeel.butt@linux.dev> <20250502001742.3087558-4-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1245D100008 X-Stat-Signature: q1htuqqroiwpx3pipyrgd1aogqwpimxj X-Rspam-User: X-HE-Tag: 1746435985-930303 X-HE-Meta: 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 ICpYRQV6 fbFtNGRv17sxqsuDd8S42/epPnXT+l1zJdSXo+zu8CWVUK7Zvelb8tJZ8i3PhcBjYE5x/VUZen4VP5oiee8xlE5/pofmiLEQhNjzK7wfFNfHXJI0QDze85ROWP7K+Gp7hvZmRcvIB1cB+Tuar7yxtJW8ErvCUAa0SD9ySxxVNTmbnKUUMmqB+psNZez5T9nfKg0rCk5hSO/4DFsOm558II7aRe9OO2/k+NlljUrrjOb8whAd4/f1PmYp0TGRq3YBcML9lxcFpCfea1CpGB7TTTWi+6XFEw5X1OZVo X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025-05-02 16:40:53 [-0700], Shakeel Butt wrote: > On Fri, May 2, 2025 at 4:28=E2=80=AFPM Alexei Starovoitov > wrote: > [...] > > > > > > > > I don't think it works. > > > > When there is a normal irq and something doing regular GFP_NOWAIT > > > > allocation gfpflags_allow_spinning() will be true and > > > > local_lock() will reenter and complain that lock->acquired is > > > > already set... but only with lockdep on. > > > > > > Yes indeed. I dropped the first patch and didn't fix this one > > > accordingly. I think the fix can be as simple as checking for > > > in_task() here instead of gfp_mask. That should work for both RT and > > > non-RT kernels. > > > > Like: > > if (in_task()) > > local_lock(...); > > else if (!local_trylock(...)) > > > > Most of the networking runs in bh, so it will be using > > local_trylock() path which is probably ok in !PREEMPT_RT, > > but will cause random performance issues in PREEMP_RT, > > since rt_spin_trylock() will be randomly failing and taking > > slow path of charging. It's not going to cause permanent > > nginx 3x regression :), but unlucky slowdowns will be seen. > > A task can grab that per-cpu rt_spin_lock and preempted > > by network processing. >=20 > Does networking run in bh for PREEMPT_RT as well? It does but BH is preemptible. > I think I should get networking & RT folks opinion on this one. I will > decouple this irq patch from the decoupling lock patches and start a > separate discussion thread. Sebastian