Re: [PATCH v6 8/9] mm: multigenerational lru: user interface

From: Yu Zhao <yuzhao@google•com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux•ibm.com>
Cc: Andrew Morton <akpm@linux-foundation•org>,
	Linus Torvalds <torvalds@linux-foundation•org>,
	Andi Kleen <ak@linux•intel.com>,
	Catalin Marinas <catalin.marinas@arm•com>,
	Dave Hansen <dave.hansen@linux•intel.com>,
	Hillf Danton <hdanton@sina•com>, Jens Axboe <axboe@kernel•dk>,
	Jesse Barnes <jsbarnes@google•com>,
	Johannes Weiner <hannes@cmpxchg•org>,
	Jonathan Corbet <corbet@lwn•net>,
	Matthew Wilcox <willy@infradead•org>,
	Mel Gorman <mgorman@suse•de>,
	Michael Larabel <Michael@michaellarabel•com>,
	Michal Hocko <mhocko@kernel•org>, Rik van Riel <riel@surriel•com>,
	Vlastimil Babka <vbabka@suse•cz>, Will Deacon <will@kernel•org>,
	Ying Huang <ying.huang@intel•com>,
	linux-arm-kernel@lists•infradead.org, linux-doc@vger•kernel.org,
	linux-kernel@vger•kernel.org, linux-mm@kvack•org,
	page-reclaim@google•com, x86@kernel•org,
	Konstantin Kharlamov <Hi-Angel@yandex•ru>
Subject: Re: [PATCH v6 8/9] mm: multigenerational lru: user interface
Date: Thu, 13 Jan 2022 23:50:15 -0700	[thread overview]
Message-ID: <YeEdJxLdUaxEGBBP@google.com> (raw)
In-Reply-To: <877db2opve.fsf@linux.ibm.com>

On Fri, Jan 14, 2022 at 10:50:05AM +0530, Aneesh Kumar K.V wrote:
> Yu Zhao <yuzhao@google•com> writes:
> > On Thu, Jan 13, 2022 at 04:01:31PM +0530, Aneesh Kumar K.V wrote:
> >> Yu Zhao <yuzhao@google•com> writes:
> >> 
> >> > Add /sys/kernel/mm/lru_gen/enabled as a runtime kill switch.
> >> 
> >> Got the below lockdep warning while using the above kill/enable switch
> >> 
> >> 
> >> [   84.252952] ======================================================
> >> [   84.253012] WARNING: possible circular locking dependency detected
> >> [   84.253074] 5.16.0-rc8-16204-g1cdcf1120b31 #511 Not tainted
> >> [   84.253135] ------------------------------------------------------
> >> [   84.253194] bash/2862 is trying to acquire lock:
> >> [   84.253243] c0000000021ff740 (cgroup_mutex){+.+.}-{3:3}, at: store_enable+0x80/0x1510
> >> [   84.253340]
> >>                but task is already holding lock:
> >> [   84.253410] c000000002221348 (mem_hotplug_lock){++++}-{0:0}, at: mem_hotplug_begin+0x30/0x50
> >> [   84.253503]
> >>                which lock already depends on the new lock.
> >> 
> >> [   84.255933] Chain exists of:
> >>                  cgroup_mutex --> cpu_hotplug_lock --> mem_hotplug_lock
> >
> > Thanks. Will reverse the order between mem_hotplug_lock and
> > cgroup_mutex in the next spin.
> 
> It also needs the unlocked variant of static_key_enable/disable.

Right. This is what I have at the moment. Tested with QEMU memory
hotplug. Can you please give it try too? Thanks.

    cgroup_lock()
    cpus_read_lock()
    get_online_mems()

        if (enable)
            static_branch_enable_cpuslocked()
        else
            static_branch_disable_cpuslocked()

    put_online_mems()
    cpus_read_unlock()
    cgroup_unlock()

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