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    Subject[RFC][PATCH 1/5] change swap cache interfaces
    From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    In following patch, usage of swap cache will be recorded into swap_map.
    This patch is for necessary interface changes to do that.

    2 interfaces:
    - swapcache_prepare()
    - swapcache_free()
    is added for allocating/freeing refcnt from swap-cache to existing
    swap entries. But implementation itself is not changed under this patch.
    At adding swapcache_free(), memcg's hook code is moved under swapcache_free().
    This is better than using scattered hooks.

    Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    ---
    include/linux/swap.h | 7 +++++++
    mm/swap_state.c | 11 +++++------
    mm/swapfile.c | 19 +++++++++++++++++++
    mm/vmscan.c | 3 +--
    4 files changed, 32 insertions(+), 8 deletions(-)
    Index: new-trial-swapcount/include/linux/swap.h
    ===================================================================
    --- new-trial-swapcount.orig/include/linux/swap.h
    +++ new-trial-swapcount/include/linux/swap.h
    @@ -301,8 +301,10 @@ 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 int swapcache_prepare(swp_entry_t);
    extern int valid_swaphandles(swp_entry_t, unsigned long *);
    extern void swap_free(swp_entry_t);
    +extern void swapcache_free(swp_entry_t, struct page *page);
    extern int free_swap_and_cache(swp_entry_t);
    extern int swap_type_of(dev_t, sector_t, struct block_device **);
    extern unsigned int count_swap_pages(int, int);
    @@ -371,11 +373,16 @@ 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_free(swp_entry_t swp)
    {
    }

    +static inline void swapcache_free(swp_entry_t swp, struct page *page)
    +{
    +}
    +
    static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
    struct vm_area_struct *vma, unsigned long addr)
    {
    Index: new-trial-swapcount/mm/swap_state.c
    ===================================================================
    --- new-trial-swapcount.orig/mm/swap_state.c
    +++ new-trial-swapcount/mm/swap_state.c
    @@ -162,11 +162,11 @@ int add_to_swap(struct page *page)
    return 1;
    case -EEXIST:
    /* Raced with "speculative" read_swap_cache_async */
    - swap_free(entry);
    + swapcache_free(entry, NULL);
    continue;
    default:
    /* -ENOMEM radix-tree allocation failure */
    - swap_free(entry);
    + swapcache_free(entry, NULL);
    return 0;
    }
    }
    @@ -188,8 +188,7 @@ void delete_from_swap_cache(struct page
    __delete_from_swap_cache(page);
    spin_unlock_irq(&swapper_space.tree_lock);

    - mem_cgroup_uncharge_swapcache(page, entry);
    - swap_free(entry);
    + swapcache_free(entry, page);
    page_cache_release(page);
    }

    @@ -293,7 +292,7 @@ struct page *read_swap_cache_async(swp_e
    /*
    * Swap entry may have been freed since our caller observed it.
    */
    - if (!swap_duplicate(entry))
    + if (!swapcache_prepare(entry))
    break;

    /*
    @@ -317,7 +316,7 @@ struct page *read_swap_cache_async(swp_e
    }
    ClearPageSwapBacked(new_page);
    __clear_page_locked(new_page);
    - swap_free(entry);
    + swapcache_free(entry, NULL);
    } while (err != -ENOMEM);

    if (new_page)
    Index: new-trial-swapcount/mm/swapfile.c
    ===================================================================
    --- new-trial-swapcount.orig/mm/swapfile.c
    +++ new-trial-swapcount/mm/swapfile.c
    @@ -510,6 +510,16 @@ void swap_free(swp_entry_t entry)
    }

    /*
    + * Called after dropping swapcache to decrease refcnt to swap entries.
    + */
    +void swapcache_free(swp_entry_t entry, struct page *page)
    +{
    + if (page)
    + mem_cgroup_uncharge_swapcache(page, entry);
    + return swap_free(entry);
    +}
    +
    +/*
    * How many references to page are currently swapped out?
    */
    static inline int page_swapcount(struct page *page)
    @@ -1979,6 +1989,15 @@ bad_file:
    goto out;
    }

    +/*
    + * Called when allocating swap cache for exising swap entry,
    + */
    +int swapcache_prepare(swp_entry_t entry)
    +{
    + return swap_duplicate(entry);
    +}
    +
    +
    struct swap_info_struct *
    get_swap_info_struct(unsigned type)
    {
    Index: new-trial-swapcount/mm/vmscan.c
    ===================================================================
    --- new-trial-swapcount.orig/mm/vmscan.c
    +++ new-trial-swapcount/mm/vmscan.c
    @@ -477,8 +477,7 @@ static int __remove_mapping(struct addre
    swp_entry_t swap = { .val = page_private(page) };
    __delete_from_swap_cache(page);
    spin_unlock_irq(&mapping->tree_lock);
    - mem_cgroup_uncharge_swapcache(page, swap);
    - swap_free(swap);
    + swapcache_free(swap, page);
    } else {
    __remove_from_page_cache(page);
    spin_unlock_irq(&mapping->tree_lock);


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