Re: [PATCH 2/4] modify swap_map and add SWAP_HAS_CACHE flag.

KAMEZAWA Hiroyuki
2009-05-30T11:17:01Z

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
>