linux-kernel - Re: [PATCH 2/4] modify swap_map and add SWAP_HAS

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Date:	Sat, 30 May 2009 20:16:51 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] modify swap_map and add SWAP_HAS_CACHE flag.

Balbir Singh wrote:
>>  #define SWAP_CLUSTER_MAX 32
>>
>> -#define SWAP_MAP_MAX	0x7fff
>> -#define SWAP_MAP_BAD	0x8000
>> -
>> +#define SWAP_MAP_MAX	0x7ffe
>> +#define SWAP_MAP_BAD	0x7fff
>> +#define SWAP_HAS_CACHE  0x8000		/* There is a swap cache of entry. */
>
> Why count, can't we use swp->flags?
>

Hmm ? swap_map just only a "unsiged short" value per entry..sorry,
I can't catch what you mention to.


>> +#define SWAP_COUNT_MASK (~SWAP_HAS_CACHE)
>>  /*
>>   * The in-memory structure used to track swap areas.
>>   */
>> @@ -300,7 +301,7 @@ extern long total_swap_pages;
>>  extern void si_swapinfo(struct sysinfo *);
>>  extern swp_entry_t get_swap_page(void);
>>  extern swp_entry_t get_swap_page_of_type(int);
>> -extern int swap_duplicate(swp_entry_t);
>> +extern void swap_duplicate(swp_entry_t);
>>  extern int swapcache_prepare(swp_entry_t);
>>  extern int valid_swaphandles(swp_entry_t, unsigned long *);
>>  extern void swap_free(swp_entry_t);
>> @@ -372,9 +373,12 @@ static inline void show_swap_cache_info(
>>  }
>>
>>  #define free_swap_and_cache(swp)	is_migration_entry(swp)
>> -#define swap_duplicate(swp)		is_migration_entry(swp)
>>  #define swapcache_prepare(swp)		is_migration_entry(swp)
>>
>> +static inline void swap_duplicate(swp_entry_t swp)
>> +{
>> +}
>> +
>>  static inline void swap_free(swp_entry_t swp)
>>  {
>>  }
>> Index: new-trial-swapcount2/mm/swapfile.c
>> ===================================================================
>> --- new-trial-swapcount2.orig/mm/swapfile.c
>> +++ new-trial-swapcount2/mm/swapfile.c
>> @@ -53,6 +53,26 @@ static struct swap_info_struct swap_info
>>
>>  static DEFINE_MUTEX(swapon_mutex);
>>
>> +/* For reference count accounting in swap_map */
>> +static inline int swap_count(unsigned short ent)
>> +{
>> +	return ent & SWAP_COUNT_MASK;
>> +}
>> +
>> +static inline int swap_has_cache(unsigned short ent)
>> +{
>> +	return ent & SWAP_HAS_CACHE;
>> +}
>> +
>> +static inline unsigned short make_swap_count(int count, int has_cache)
>> +{
>> +	unsigned short ret = count;
>> +
>> +	if (has_cache)
>> +		return SWAP_HAS_CACHE | ret;
>> +	return ret;
>> +}
>
> make_swap_count() does not make too much sense in terms of the name
> for the function. Should it be called generate_swap_count or
> assign_swap_count_info?

Hmm ? ok, rename this as generate_swap_count(). or
generate_swapmap_info().



>> +
>>  /*
>>   * We need this because the bdev->unplug_fn can sleep and we cannot
>>   * hold swap_lock while calling the unplug_fn. And swap_lock
>> @@ -167,7 +187,8 @@ static int wait_for_discard(void *word)
>>  #define SWAPFILE_CLUSTER	256
>>  #define LATENCY_LIMIT		256
>>
>> -static inline unsigned long scan_swap_map(struct swap_info_struct *si)
>> +static inline unsigned long scan_swap_map(struct swap_info_struct *si,
>> +					  int cache)
>
> Can we please use bool for readability or even better an enum?
>
ok, enum.

> Looks good at first glance otherwise. I think distinguishing between
> the counts is good, but also complex. Overall the patch is useful.
>
Thank you for review.

-Kame

> --
> 	Balbir
>


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