linux-kernel - Re: [PATCH v6 01/13] mm/demotion: Add support for explicit memory tiers

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Message-ID: <20220614151352.6ykunpu3q2e7twmv@offworld>
Date:   Tue, 14 Jun 2022 08:13:52 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     Ying Huang <ying.huang@...el.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, Wei Xu <weixugc@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Yang Shi <shy828301@...il.com>,
        Tim C Chen <tim.c.chen@...el.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v6 01/13] mm/demotion: Add support for explicit memory
 tiers

>> memory_tier_lock isn't held to call register_memory_tier() in this
>> patch.  That will cause confusion.
>
>will this help to explain this better
>modified   mm/memory-tiers.c
>@@ -151,6 +151,11 @@ static void insert_memory_tier(struct memory_tier *memtier)
> 	struct list_head *ent;
> 	struct memory_tier *tmp_memtier;
>
>+	if (IS_ENABLED(CONFIG_DEBUG_VM) && !mutex_is_locked(&memory_tier_lock)) {
>+		WARN_ON_ONCE(1);
>+		return;
>+	}

Why not just use lockdep here instead?