linux-kernel - Re: [patch v3] swap: virtual swap readahead

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Date:	Thu, 11 Jun 2009 14:31:22 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.org.uk>,
	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Minchan Kim <minchan.kim@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch v3] swap: virtual swap readahead

On Tue, 9 Jun 2009 21:01:28 +0200
Johannes Weiner <hannes@...xchg.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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