linux-kernel - Re: Subject: [PATCH V6 1/4] mm: frontswap: swap data structure changes

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Message-Id: <4E414320020000780005057E@nat28.tlf.novell.com>
Date:	Tue, 09 Aug 2011 13:24:32 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Dan Magenheimer" <dan.magenheimer@...cle.com>
Cc:	<hannes@...xchg.org>, <jackdachef@...il.com>, <hughd@...gle.com>,
	<jeremy@...p.org>, <npiggin@...nel.dk>, <linux-mm@...ck.org>,
	<akpm@...ux-foundation.org>, <sjenning@...ux.vnet.ibm.com>,
	<chris.mason@...cle.com>, <konrad.wilk@...cle.com>,
	<kurt.hackel@...cle.com>, <riel@...hat.com>, <ngupta@...are.org>,
	<linux-kernel@...r.kernel.org>, <matthew@....cx>
Subject: Re: Subject: [PATCH V6 1/4] mm: frontswap: swap data structure
	 changes

>>> On 08.08.11 at 22:45, Dan Magenheimer <dan.magenheimer@...cle.com> wrote:
> From: Dan Magenheimer <dan.magenheimer@...cle.com>
> Subject: [PATCH V6 1/4] mm: frontswap: swap data structure changes
> 
> This first patch of four in the frontswap series makes available core
> swap data structures (swap_lock, swap_list and swap_info) that are
> needed by frontswap.c but we don't need to expose them to the dozens
> of files that include swap.h so we create a new swapfile.h just to
> extern-ify these.
> 
> Also add frontswap-related elements to swap_info_struct.  Frontswap_map
> points to vzalloc'ed one-bit-per-swap-page metadata that indicates
> whether the swap page is in frontswap or in the device and frontswap_pages
> counts how many pages are in frontswap.  We don't tie these to
> CONFIG_FRONTSWAP to avoid unnecessary clutter around various frontswap
> hooks.
> 
> [v6: rebase to 3.0-rc1]
> [v5: no change from v4]
> [v4: rebase to 2.6.39]
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> Reviewed-by: Konrad Wilk <konrad.wilk@...cle.com>
> Acked-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> Cc: Jeremy Fitzhardinge <jeremy@...p.org>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Nitin Gupta <ngupta@...are.org>
> Cc: Matthew Wilcox <matthew@....cx>
> Cc: Chris Mason <chris.mason@...cle.com>
> Cc: Jan Beulich <JBeulich@...ell.com>
> Cc: Rik Riel <riel@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> 
> --- linux/include/linux/swapfile.h	1969-12-31 17:00:00.000000000 -0700
> +++ frontswap/include/linux/swapfile.h	2011-08-08 08:59:03.951694506 -0600
> @@ -0,0 +1,13 @@
> +#ifndef _LINUX_SWAPFILE_H
> +#define _LINUX_SWAPFILE_H
> +
> +/*
> + * these were static in swapfile.c but frontswap.c needs them and we don't
> + * want to expose them to the dozens of source files that include swap.h
> + */
> +extern spinlock_t swap_lock;
> +extern struct swap_list_t swap_list;
> +extern struct swap_info_struct *swap_info[];
> +extern int try_to_unuse(unsigned int, bool, unsigned long);
> +
> +#endif /* _LINUX_SWAPFILE_H */
> --- linux/include/linux/swap.h	2011-08-08 08:19:25.880690134 -0600
> +++ frontswap/include/linux/swap.h	2011-08-08 08:59:03.952691415 -0600
> @@ -194,6 +194,8 @@ struct swap_info_struct {
>  	struct block_device *bdev;	/* swap device or bdev of swap file */
>  	struct file *swap_file;		/* seldom referenced */
>  	unsigned int old_block_size;	/* seldom referenced */

#ifdef CONFIG_FRONTSWAP

> +	unsigned long *frontswap_map;	/* frontswap in-use, one bit per page */
> +	unsigned int frontswap_pages;	/* frontswap pages in-use counter */


#endif

(to eliminate any overhead with that config option unset)

Jan

>  };
>  
>  struct swap_list_t {



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