From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH 1/1] psi: remove 500ms min window size limitation for triggers Date: Thu, 2 Mar 2023 18:39:47 +0100 Message-ID: References: <20230301193403.1507484-1-surenb@google.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1677778788; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=JMuTmf0F+QOiaF6t8tr3QA/L27lx/sQSTLa4V7SznDY=; b=LMYMDQKMZ7Qo4VvbYjlK3lmM/OKd2359yCXU2EFKolo15/dL8xBx9RP656ePv9oxTz6Y6w NEgXosiAyJ9ADKeU2+xveaIYxq6bzCVR6VFy6q0dHg/X81EQgsU4m6E7vbDNtZCALw8XTg tWyvo1svOgHpf077fXJ4vguWReYVanU= Content-Disposition: inline In-Reply-To: List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Suren Baghdasaryan Cc: tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org, peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, johunt-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org, keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org, quic_sudaraja-jfJNa2p1gH1BDgjK7y7TUQ@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Thu 02-03-23 08:08:38, Suren Baghdasaryan wrote: > On Thu, Mar 2, 2023 at 5:58 AM Michal Hocko wrote: > > > > On Wed 01-03-23 11:34:03, Suren Baghdasaryan wrote: > > > Current 500ms min window size for psi triggers limits polling interval > > > to 50ms to prevent polling threads from using too much cpu bandwidth by > > > polling too frequently. However the number of cgroups with triggers is > > > unlimited, so this protection can be defeated by creating multiple > > > cgroups with psi triggers (triggers in each cgroup are served by a single > > > "psimon" kernel thread). > > > Instead of limiting min polling period, which also limits the latency of > > > psi events, it's better to limit psi trigger creation to authorized users > > > only, like we do for system-wide psi triggers (/proc/pressure/* files can > > > be written only by processes with CAP_SYS_RESOURCE capability). This also > > > makes access rules for cgroup psi files consistent with system-wide ones. > > > Add a CAP_SYS_RESOURCE capability check for cgroup psi file writers and > > > remove the psi window min size limitation. > > > > > > Suggested-by: Sudarshan Rajagopalan > > > Link: https://lore.kernel.org/all/cover.1676067791.git.quic_sudaraja-jfJNa2p1gH1BDgjK7y7TUQ@public.gmane.org/ > > > Signed-off-by: Suren Baghdasaryan > > > > Acked-by: Michal Hocko > > > > with this to fix > > [...] > > > @@ -1278,8 +1277,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, > > > if (state >= PSI_NONIDLE) > > > return ERR_PTR(-EINVAL); > > > > > > - if (window_us < WINDOW_MIN_US || > > > - window_us > WINDOW_MAX_US) > > > + if (window_us <= 0 || window_us > WINDOW_MAX_US) > > > return ERR_PTR(-EINVAL); > > > > window_us is u32 sp the check for <= 0 doesn't make any sense. > > Completely missed that. Will change to == 0 and post the new version. I was about to asky check for 0 actually matters but maybe a future extension might give it a special meaning so it is likely a good idea to EINVAL on 0 now. You can keep my ack on that change -- Michal Hocko SUSE Labs