linux-kernel - Re: [PATCH 10/15] mm/swap: break the loop if matching device is found

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Message-Id: <20220509141602.b6be120b80d0ab3218fe619a@linux-foundation.org>
Date:   Mon, 9 May 2022 14:16:02 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     <willy@...radead.org>, <vbabka@...e.cz>, <dhowells@...hat.com>,
        <neilb@...e.de>, <apopple@...dia.com>, <david@...hat.com>,
        <surenb@...gle.com>, <peterx@...hat.com>,
        <naoya.horiguchi@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/15] mm/swap: break the loop if matching device is
 found

On Mon, 9 May 2022 21:14:11 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:

> We can break the loop if matching device is found to save some possible
> cpu cycles because there should be only one matching device and there is
> no need to continue if the matching one is already found.
> 
> ...
>
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1692,6 +1692,8 @@ int swap_type_of(dev_t device, sector_t offset)
>  				spin_unlock(&swap_lock);
>  				return type;
>  			}
> +
> +			break;
>  		}
>  	}
>  	spin_unlock(&swap_lock);

Are you sure?  If we have two S_ISREG swapfiles on the same device,
don't they have the same sis->bdev?

If not, why bother passing `offset' into this function at all?