Date: Thu, 11 Jun 2009 14:31:22 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>,
       Hugh Dickins <hugh.dickins@tiscali.org.uk>,
       Andi Kleen <andi@firstfloor.org>, Wu Fengguang <fengguang.wu@intel.com>,
       Minchan Kim <minchan.kim@gmail.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org
Subject: Re: [patch v3] swap: virtual swap readahead
Message-Id: <20090611143122.108468f1.kamezawa.hiroyu@jp.fujitsu.com>
In-Reply-To: <20090609190128.GA1785@cmpxchg.org>
References: <20090609190128.GA1785@cmpxchg.org>
Organization: FUJITSU Co. LTD.
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On Tue, 9 Jun 2009 21:01:28 +0200
Johannes Weiner <hannes@cmpxchg.org> wrote:
> [resend with lists cc'd, sorry]
> 
> +static int swap_readahead_ptes(struct mm_struct *mm,
> +			unsigned long addr, pmd_t *pmd,
> +			swp_entry_t *entries,
> +			unsigned long cluster)
> +{
> +	unsigned long window, min, max, limit;
> +	spinlock_t *ptl;
> +	pte_t *ptep;
> +	int i, nr;
> +
> +	window = cluster << PAGE_SHIFT;
> +	min = addr & ~(window - 1);
> +	max = min + cluster;

Johannes, I wonder there is no reason to use "alignment".
I think we just need to read "nearby" pages. Then, this function's
scan range should be

	[addr - window/2, addr + window/2)
or some.

And here, too
> +	if (!entries)	/* XXX: shmem case */
> +		return swapin_readahead_phys(entry, gfp_mask, vma, addr);
> +	pmin = swp_offset(entry) & ~(cluster - 1);
> +	pmax = pmin + cluster;

pmin = swp_offset(entry) - cluster/2.
pmax = swp_offset(entry) + cluster/2.

I'm sorry if I miss a reason for using "alignment".

Thanks,
-Kame


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