[PATCH 1/4] add swap cache interface for swap reference v2 (updated)

KAMEZAWA Hiroyuki
2009-05-29T05:39:45Z

On Fri, 29 May 2009 14:08:32 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > 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.
>
here.

==

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.

Changelog: v1->v2
- fixed shmem_writepage() error path.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
include/linux/swap.h | 7 +++++++
mm/shmem.c | 2 +-
mm/swap_state.c | 11 +++++------
mm/swapfile.c | 19 +++++++++++++++++++
mm/vmscan.c | 3 +--
5 files changed, 33 insertions(+), 9 deletions(-)

Index: mmotm-2.6.30-May28/include/linux/swap.h
===================================================================
--- mmotm-2.6.30-May28.orig/include/linux/swap.h
+++ mmotm-2.6.30-May28/include/linux/swap.h
@@ -282,8 +282,10 @@ 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);
@@ -352,11 +354,16 @@ 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: mmotm-2.6.30-May28/mm/swap_state.c
===================================================================
--- mmotm-2.6.30-May28.orig/mm/swap_state.c
+++ mmotm-2.6.30-May28/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: mmotm-2.6.30-May28/mm/swapfile.c
===================================================================
--- mmotm-2.6.30-May28.orig/mm/swapfile.c
+++ mmotm-2.6.30-May28/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: mmotm-2.6.30-May28/mm/vmscan.c
===================================================================
--- mmotm-2.6.30-May28.orig/mm/vmscan.c
+++ mmotm-2.6.30-May28/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);
Index: mmotm-2.6.30-May28/mm/shmem.c
===================================================================
--- mmotm-2.6.30-May28.orig/mm/shmem.c
+++ mmotm-2.6.30-May28/mm/shmem.c
@@ -1097,7 +1097,7 @@ static int shmem_writepage(struct page *
shmem_swp_unmap(entry);
unlock:
spin_unlock(&info->lock);
- swap_free(swap);
+ swapcache_free(swap, NULL);
redirty:
set_page_dirty(page);
if (wbc->for_reclaim)