From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: Re: [PATCH] mm/memcg: Do not check v1 event counter when not needed Date: Tue, 18 Jan 2022 20:57:17 +0100 Message-ID: References: <20220118182600.15007-1-mkoutny@suse.com> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1642535839; 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=ekB+1/vJxKtPMPKgiG7Ixi8Eki0Fc2E/bH0E5cSRR1U=; b=fHbWgepw/aDQjBLvnCI80P8N8EsYANtaojRx+/2VtR2gTR96Znt6hFYewAfcs4Cgi60vhg OAKzIpQyKV22TsLsIYGs+OtmNWqM6tFcgBNpBZ1xZoREsQhx9zo1thIl71HhSu97f0Sn2D 30C4qXVtet1nPP2RmbxVLJmrk8bc9qXqe92BxzP3qhexJisiADg8HX0JtMy4QQ5hTVych7 hV2qt/+L1CANDPUWnDb76dbxNEyhcneBAe7MmNoma6GdFuOmwHGwn00sseFz+refXsyBnz yWtege5K79p81K9pBAyGfwY0MZ5R3ffsaioyn8nif07fUHPYDuTaIjI82FX3yw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1642535839; 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=ekB+1/vJxKtPMPKgiG7Ixi8Eki0Fc2E/bH0E5cSRR1U=; b=JSgnI20eM18xM0ejtTlxLGa5wEIFBRjVgZdESG86vOupEzU6H4EPwN/ilnrRzKM04mVLQo 3sFvJfzJRcZJdvAg== Content-Disposition: inline In-Reply-To: <20220118182600.15007-1-mkoutny-IBi9RG/b67k@public.gmane.org> List-ID: Content-Type: text/plain; charset="utf-8" To: Michal =?utf-8?Q?Koutn=C3=BD?= Cc: akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org, vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org On 2022-01-18 19:26:00 [+0100], Michal Koutn=C3=BD wrote: > I think it would make sense inserting the patch into your series and > subsequently reject enabling on PREEMPT_RT -- provided this patch makes s= ense > to others too -- the justification is rather functionality splitting for > this PREEMPT_RT effort. Interesting. So while looking at this today I came up with the patch at the bottom. The other things I had looked way uglier and then since nobody probably will use it=E2=80=A6 Let me know how you want it to be integrated. ------>8------ =46rom: Sebastian Andrzej Siewior Date: Tue, 18 Jan 2022 17:28:07 +0100 Subject: [PATCH] mm/memcg: Disable threshold event handlers on PREEMPT_RT MIME-Version: 1.0 Content-Type: text/plain; charset=3DUTF-8 Content-Transfer-Encoding: 8bit During the integration of PREEMPT_RT support, the code flow around memcg_check_events() resulted in `twisted code'. Moving the code around and avoiding then would then lead to an additional local-irq-save section within memcg_check_events(). While looking better, it adds a local-irq-save section to code flow which is usually within an local-irq-save block. The threshold event handler is a deprecated memcg v1 feature. Instead of trying to get it to work under PREEMPT_RT just disable it. There should have not been any users on PREEMPT_RT. From that perspective makes it even less sense to get it to work under PREEMPT_RT while having zero users. Make memory.soft_limit_in_bytes and cgroup.event_control return -EOPNOTSUPP on PREEMPT_RT. Make memcg_check_events() empty on PREEMPT_RT since it won't do anything. Document that the two knobs are disabled on PREEMPT_RT. Suggested-by: Michal Hocko Suggested-by: Michal Koutn=C3=BD Signed-off-by: Sebastian Andrzej Siewior --- Documentation/admin-guide/cgroup-v1/memory.rst | 2 ++ mm/memcontrol.c | 12 ++++++++++++ 2 files changed, 14 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation= /admin-guide/cgroup-v1/memory.rst index faac50149a222..2cc502a75ef64 100644 --- a/Documentation/admin-guide/cgroup-v1/memory.rst +++ b/Documentation/admin-guide/cgroup-v1/memory.rst @@ -64,6 +64,7 @@ Brief summary of control files. threads cgroup.procs show list of processes cgroup.event_control an interface for event_fd() + This knob is not available on CONFIG_PREEMPT_RT systems. memory.usage_in_bytes show current usage for memory (See 5.5 for details) memory.memsw.usage_in_bytes show current usage for memory+Swap @@ -75,6 +76,7 @@ Brief summary of control files. memory.max_usage_in_bytes show max memory usage recorded memory.memsw.max_usage_in_bytes show max memory+Swap usage recorded memory.soft_limit_in_bytes set/show soft limit of memory usage + This knob is not available on CONFIG_PREEMPT_RT systems. memory.stat show various statistics memory.use_hierarchy set/show hierarchical account enabled This knob is deprecated and shouldn't= be diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 2ed5f2a0879d3..3c4f7a0fd0039 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -821,6 +821,7 @@ static void mem_cgroup_charge_statistics(struct mem_cgr= oup *memcg, __this_cpu_add(memcg->vmstats_percpu->nr_page_events, nr_pages); } =20 +#ifndef CONFIG_PREEMPT_RT static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg, enum mem_cgroup_events_target target) { @@ -864,6 +865,9 @@ static void memcg_check_events(struct mem_cgroup *memcg= , int nid) mem_cgroup_update_tree(memcg, nid); } } +#else +static void memcg_check_events(struct mem_cgroup *memcg, int nid) { } +#endif =20 struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p) { @@ -3751,8 +3755,12 @@ static ssize_t mem_cgroup_write(struct kernfs_open_f= ile *of, } break; case RES_SOFT_LIMIT: +#ifndef CONFIG_PREEMPT_RT memcg->soft_limit =3D nr_pages; ret =3D 0; +#else + ret =3D -EOPNOTSUPP; +#endif break; } return ret ?: nbytes; @@ -4717,6 +4725,7 @@ static void memcg_event_ptable_queue_proc(struct file= *file, static ssize_t memcg_write_event_control(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { +#ifndef CONFIG_PREEMPT_RT struct cgroup_subsys_state *css =3D of_css(of); struct mem_cgroup *memcg =3D mem_cgroup_from_css(css); struct mem_cgroup_event *event; @@ -4843,6 +4852,9 @@ static ssize_t memcg_write_event_control(struct kernf= s_open_file *of, kfree(event); =20 return ret; +#else + return -EOPNOTSUPP; +#endif } =20 static struct cftype mem_cgroup_legacy_files[] =3D { --=20 2.34.1