On 2024/2/20 12:53, Sergey Senozhatsky wrote:
> On (24/02/20 12:51), Chengming Zhou wrote:
>> On 2024/2/20 12:48, Sergey Senozhatsky wrote:
>>> On (24/02/19 13:33), Chengming Zhou wrote:
>>>> static void migrate_write_unlock(struct zspage *zspage)
>>>> {
>>>> write_unlock(&zspage->lock);
>>>> @@ -2003,19 +1997,17 @@ static unsigned long __zs_compact(struct zs_pool *pool,
>>>> dst_zspage = isolate_dst_zspage(class);
>>>> if (!dst_zspage)
>>>> break;
>>>> - migrate_write_lock(dst_zspage);
>>>> }
>>>>
>>>> src_zspage = isolate_src_zspage(class);
>>>> if (!src_zspage)
>>>> break;
>>>>
>>>> - migrate_write_lock_nested(src_zspage);
>>>> -
>>>> + migrate_write_lock(src_zspage);
>>>> migrate_zspage(pool, src_zspage, dst_zspage);
>>>> - fg = putback_zspage(class, src_zspage);
>>>> migrate_write_unlock(src_zspage);
>>>>
>>>> + fg = putback_zspage(class, src_zspage);
>>>
>>> Hmm. Lockless putback doesn't look right to me. We modify critical
>>> zspage fileds in putback_zspage().
>>
>> Which I think is protected by pool->lock, right? We already held it.
>
> Not really. We have, for example, the following patterns:
>
> get_zspage_mapping()
> spin_lock(&pool->lock)
Right, this pattern is not safe actually, since we can't get stable fullness
value of zspage outside pool->lock.
But this pattern usage is only used in free_zspage path, so should be ok.
Actually we don't use the fullness value returned from get_zspage_mapping()
in the free_zspage() path, only use the class value to get the class.
Anyway, this pattern is confusing, I think we should clean up that?
Thanks.
