linux-kernel - Re: [PATCH 06/15] mm/swap: remove buggy cache->nr check in refill_swap_slots

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Date:   Thu, 12 May 2022 15:37:13 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     willy@...radead.org, vbabka@...e.cz, dhowells@...hat.com,
        neilb@...e.de, apopple@...dia.com, surenb@...gle.com,
        peterx@...hat.com, naoya.horiguchi@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/15] mm/swap: remove buggy cache->nr check in
 refill_swap_slots_cache

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.

> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.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.


Anyhow,

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb