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

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Message-ID: <YeEdJxLdUaxEGBBP@google.com>
Date:   Thu, 13 Jan 2022 23:50:15 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        page-reclaim@...gle.com, x86@...nel.org,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>
Subject: Re: [PATCH v6 8/9] mm: multigenerational lru: user interface

On Fri, Jan 14, 2022 at 10:50:05AM +0530, Aneesh Kumar K.V wrote:
> Yu Zhao <yuzhao@...gle.com> writes:
> > On Thu, Jan 13, 2022 at 04:01:31PM +0530, Aneesh Kumar K.V wrote:
> >> Yu Zhao <yuzhao@...gle.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()