linux-kernel - Re: [PATCH 03/10] readahead: combine file_ra_state.prev_index/prev_offset into prev

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Message-Id: <20070723205535.d08338fc.akpm@linux-foundation.org>
Date:	Mon, 23 Jul 2007 20:55:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Fengguang Wu <wfg@...l.ustc.edu.cn>
Cc:	linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 03/10] readahead: combine
 file_ra_state.prev_index/prev_offset into prev_pos

On Tue, 24 Jul 2007 10:00:12 +0800 Fengguang Wu <wfg@...l.ustc.edu.cn> wrote:

> @@ -342,11 +342,9 @@ ondemand_readahead(struct address_space 
>  		   bool hit_readahead_marker, pgoff_t offset,
>  		   unsigned long req_size)
>  {
> -	int max;	/* max readahead pages */
> -	int sequential;
> -
> -	max = ra->ra_pages;
> -	sequential = (offset - ra->prev_index <= 1UL) || (req_size > max);
> +	int	max = ra->ra_pages;	/* max readahead pages */
> +	pgoff_t prev_offset;
> +	int	sequential;
>  
>  	/*
>  	 * It's the expected callback offset, assume sequential access.
> @@ -360,6 +358,9 @@ ondemand_readahead(struct address_space 
>  		goto readit;
>  	}
>  
> +	prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT;
> +	sequential = offset - prev_offset <= 1UL || req_size > max;

It's a bit pointless using an opaque type for prev_offset here, and then
encoding the knowledge that it is implemented as "unsigned long".

It's a minor thing, but perhaps just "<= 1" would make more sense here.
-
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