Re: [PATCH 1/4] add swap cache interface for swap reference

Daisuke Nishimura
2009-05-29T05:05:27Z

On Thu, 28 May 2009 14:10:49 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 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.
>
IIUC, swap_free() at the end of shmem_writepage() should also be changed to swapcache_free().

Thanks,
Daisuke Nishimura.

> 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-swapcount2/include/linux/swap.h
> ===================================================================
> --- new-trial-swapcount2.orig/include/linux/swap.h
> +++ new-trial-swapcount2/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-swapcount2/mm/swap_state.c
> ===================================================================
> --- new-trial-swapcount2.orig/mm/swap_state.c
> +++ new-trial-swapcount2/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-swapcount2/mm/swapfile.c
> ===================================================================
> --- new-trial-swapcount2.orig/mm/swapfile.c
> +++ new-trial-swapcount2/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-swapcount2/mm/vmscan.c
> ===================================================================
> --- new-trial-swapcount2.orig/mm/vmscan.c
> +++ new-trial-swapcount2/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);
>