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Message-ID: <87a6afmzaq.fsf@linux.ibm.com>
Date: Tue, 14 Jun 2022 13:50:29 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To: Ying Huang <ying.huang@...el.com>, linux-mm@...ck.org,
akpm@...ux-foundation.org
Cc: Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
Yang Shi <shy828301@...il.com>,
Davidlohr Bueso <dave@...olabs.net>,
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
Ying Huang <ying.huang@...el.com> writes:
....
>
>> All those functions are called with memory_tier_lock_held. Infact all
>> list operations requires that lock held. What details do you suggest we
>> document? I can add extra comment to the mutex itself? Adding locking
>> details to all the functions will be duplicating the same details at
>> multiple places?
>
> 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;
+ }
+
list_for_each(ent, &memory_tiers) {
tmp_memtier = list_entry(ent, struct memory_tier, list);
if (tmp_memtier->rank < memtier->rank) {
@@ -811,8 +816,12 @@ static int __init memory_tier_init(void)
/*
* Register only default memory tier to hide all empty
- * memory tier from sysfs.
+ * memory tier from sysfs. Since this is early during
+ * boot, we could avoid holding memtory_tier_lock. But
+ * keep it simple by holding locks. We can add lock
+ * held debug checks in other functions.
*/
+ mutex_lock(&memory_tier_lock);
memtier = register_memory_tier(DEFAULT_MEMORY_TIER,
get_rank_from_tier(DEFAULT_MEMORY_TIER));
@@ -828,6 +837,7 @@ static int __init memory_tier_init(void)
NODE_DATA(node)->memtier = memtier;
node_set(node, memtier->nodelist);
}
+ mutex_unlock(&memory_tier_lock);
migrate_on_reclaim_init();
return 0;
-aneesh
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