linux-kernel - Re: [PATCH] mm/swap_slots.c: Remove unnecessary NULL pointer check

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Message-ID: <20210109174016.GA35215@casper.infradead.org>
Date:   Sat, 9 Jan 2021 17:40:16 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/swap_slots.c: Remove unnecessary NULL pointer check

On Sat, Jan 09, 2021 at 03:09:43AM -0500, Miaohe Lin wrote:
> The cache->slots and cache->slots_ret is already checked before we try to
> drain it. And kvfree can handle the NULL pointer itself. So remove the
> NULL pointer check here.

> @@ -178,7 +178,7 @@ static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
>  		swapcache_free_entries(cache->slots + cache->cur, cache->nr);
>  		cache->cur = 0;
>  		cache->nr = 0;
> -		if (free_slots && cache->slots) {
> +		if (free_slots) {

Prove that swapcache_free_entries() doesn't change cache->slots.

> @@ -188,13 +188,12 @@ static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
>  		spin_lock_irq(&cache->free_lock);
>  		swapcache_free_entries(cache->slots_ret, cache->n_ret);
>  		cache->n_ret = 0;
> -		if (free_slots && cache->slots_ret) {
> +		if (free_slots) {

... or ->slots_ret

> -		if (slots)
> -			kvfree(slots);
> +		kvfree(slots);

This is fine.