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Subject: Re: [PATCH 06/15] mm/swap: remove buggy cache->nr check in
 refill_swap_slots_cache
To:     David Hildenbrand <david@redhat.com>, <akpm@linux-foundation.org>
CC:     <willy@infradead.org>, <vbabka@suse.cz>, <dhowells@redhat.com>,
        <neilb@suse.de>, <apopple@nvidia.com>, <surenb@google.com>,
        <peterx@redhat.com>, <naoya.horiguchi@nec.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
References: <20220509131416.17553-1-linmiaohe@huawei.com>
 <20220509131416.17553-7-linmiaohe@huawei.com>
 <fd5c6a00-ea0e-b5d8-999f-d7b65c193ae4@redhat.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <8b03aa8a-5023-6915-64c6-f6f298f19f36@huawei.com>
Date:   Mon, 16 May 2022 10:00:43 +0800
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On 2022/5/12 21:37, David Hildenbrand wrote:
> On 09.05.22 15:14, Miaohe Lin wrote:
>> refill_swap_slots_cache is always called when cache->nr is 0. And if
>> cache->nr != 0, we should return cache->nr instead of 0. So remove
>> such buggy and confusing check.
> 
> Not sure about the "cache->nr != 0, we should return cache->nr instead
> of 0" part, I'd just drop that from the patch description. We'd actually
> end up overwriting cache->nr after your change, which doesn't sound
> right and also different to what you describe here.

Will do.

> 
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>>  mm/swap_slots.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/swap_slots.c b/mm/swap_slots.c
>> index 2f877e6f87d7..2a65a89b5b4d 100644
>> --- a/mm/swap_slots.c
>> +++ b/mm/swap_slots.c
>> @@ -258,7 +258,7 @@ void enable_swap_slots_cache(void)
>>  /* called with swap slot cache's alloc lock held */
>>  static int refill_swap_slots_cache(struct swap_slots_cache *cache)
>>  {
>> -	if (!use_swap_slot_cache || cache->nr)
>> +	if (!use_swap_slot_cache)
>>  		return 0;
>>  
>>  	cache->cur = 0;
> 
> I feel like if this function would be called with cache->nr, it would be
> a BUG. So I'm fine with removing it, but we could also think about
> turning it into some sort of WARN/BG to make it clearer that this is
> unexpected.

Since refill_swap_slots_cache is only called by folio_alloc_swap when cache->nr == 0. I think
it might be too overkill to add a WARN/BG.

> 
> 
> Anyhow,
> 
> Acked-by: David Hildenbrand <david@redhat.com>

Many thanks for comment and Acked-by tag!

>