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    SubjectRe: [PATCH 1/4] add swap cache interface for swap reference
    On Fri, 29 May 2009 13:21:53 +0900
    Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

    > 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().
    >
    Hmm!. Oh, yes. shmem_writepage()'s error path. Thank you. It will be fixed.

    Thanks,
    -Kame

    > 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);
    > >
    >



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