linux-kernel - Re: [RFC][PATCH 2/5] add SWAP_HAS_CACHE flag to swap

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Message-Id: <20090527130246.95dadb2c.nishimura@mxp.nes.nec.co.jp>
Date:	Wed, 27 May 2009 13:02:46 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [RFC][PATCH 2/5] add SWAP_HAS_CACHE flag to swap_map

> @@ -1067,21 +1113,21 @@ static int try_to_unuse(unsigned int typ
>  		}
>  
>  		/*
> -		 * How could swap count reach 0x7fff when the maximum
> -		 * pid is 0x7fff, and there's no way to repeat a swap
> -		 * page within an mm (except in shmem, where it's the
> -		 * shared object which takes the reference count)?
> -		 * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
> -		 *
> +		 * How could swap count reach 0x7ffe ?
> +		 * There's no way to repeat a swap page within an mm
> +		 * (except in shmem, where it's the shared object which takes
> +		 * the reference count)?
> +		 * We believe SWAP_MAP_MAX cannot occur.(if occur, unsigned
> +		 * short is too small....)
>  		 * If that's wrong, then we should worry more about
>  		 * exit_mmap() and do_munmap() cases described above:
>  		 * we might be resetting SWAP_MAP_MAX too early here.
>  		 * We know "Undead"s can happen, they're okay, so don't
>  		 * report them; but do report if we reset SWAP_MAP_MAX.
>  		 */
> -		if (*swap_map == SWAP_MAP_MAX) {
> +		if (swap_count(*swap_map) == SWAP_MAP_MAX) {
>  			spin_lock(&swap_lock);
> -			*swap_map = 1;
> +			*swap_map = make_swap_count(0, 1);
Can we assume the entry has SWAP_HAS_CACHE here ?
Shouldn't we check PageSwapCache beforehand ?

>  			spin_unlock(&swap_lock);
>  			reset_overflow = 1;
>  		}


Thanks,
Daisuke Nishimura.
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