linux-kernel - Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS

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Date:   Tue, 17 Jul 2018 11:32:48 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shaohua Li <shli@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with
 IS_ENABLED()

> @@ -878,6 +877,11 @@ static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
>  	unsigned long offset, i;
>  	unsigned char *map;
>  
> +	if (!IS_ENABLED(CONFIG_THP_SWAP)) {
> +		VM_WARN_ON_ONCE(1);
> +		return 0;
> +	}

I see you seized the opportunity to keep this code gloriously
unencumbered by pesky comments.  This seems like a time when you might
have slipped up and been temped to add a comment or two.  Guess not. :)

Seriously, though, does it hurt us to add a comment or two to say
something like:

	/*
	 * Should not even be attempting cluster allocations when
	 * huge page swap is disabled.  Warn and fail the allocation.
	 */
	if (!IS_ENABLED(CONFIG_THP_SWAP)) {
		VM_WARN_ON_ONCE(1);
		return 0;
	}