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SubjectImplement lookup_swap_cache for migration entries
This undoes the optimization that resulted in a yield in do_swap_cache().
do_swap_cache() stays as is. Instead we convert the migration entry to
a page * in lookup_swap_cache.

For the non swap case we need a special macro version of lookup_swap_cache
that is only capable of handling migration cache entries.

Signed-off-by: Christoph Lameter <claemter@sgi.com>

Index: linux-2.6.17-rc1-mm2/mm/swap_state.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/swap_state.c 2006-04-11 12:14:34.000000000 -0700
+++ linux-2.6.17-rc1-mm2/mm/swap_state.c 2006-04-14 09:10:03.000000000 -0700
@@ -10,6 +10,7 @@
#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
+#include <linux/swapops.h>
#include <linux/swap-prefetch.h>
#include <linux/init.h>
#include <linux/pagemap.h>
@@ -305,6 +306,12 @@ struct page * lookup_swap_cache(swp_entr
{
struct page *page;

+ if (is_migration_entry(entry)) {
+ page = migration_entry_to_page(entry);
+ get_page(page);
+ return page;
+ }
+
page = find_get_page(&swapper_space, entry.val);

if (page)
Index: linux-2.6.17-rc1-mm2/mm/memory.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/memory.c 2006-04-13 16:43:10.000000000 -0700
+++ linux-2.6.17-rc1-mm2/mm/memory.c 2006-04-14 09:04:11.000000000 -0700
@@ -1880,11 +1880,6 @@ static int do_swap_page(struct mm_struct

entry = pte_to_swp_entry(orig_pte);

- if (unlikely(is_migration_entry(entry))) {
- yield();
- goto out;
- }
-
page = lookup_swap_cache(entry);
if (!page) {
swapin_readahead(entry, address, vma);
Index: linux-2.6.17-rc1-mm2/include/linux/swap.h
===================================================================
--- linux-2.6.17-rc1-mm2.orig/include/linux/swap.h 2006-04-13 16:43:21.000000000 -0700
+++ linux-2.6.17-rc1-mm2/include/linux/swap.h 2006-04-14 09:08:42.000000000 -0700
@@ -302,7 +302,6 @@ static inline void disable_swap_token(vo
#define swap_duplicate(swp) /*NOTHING*/
#define swap_free(swp) /*NOTHING*/
#define read_swap_cache_async(swp,vma,addr) NULL
-#define lookup_swap_cache(swp) NULL
#define valid_swaphandles(swp, off) 0
#define can_share_swap_page(p) 0
#define move_to_swap_cache(p, swp) 1
@@ -311,6 +310,19 @@ static inline void disable_swap_token(vo
#define delete_from_swap_cache(p) /*NOTHING*/
#define swap_token_default_timeout 0

+/*
+ * Must use a macro for lookup_swap_cache since the functions
+ * used are only available in certain contexts.
+ */
+#define lookup_swap_cache(__swp) \
+({ struct page *p = NULL; \
+ if (is_migration_entry(__swp)) { \
+ p = migration_entry_to_page(__swp); \
+ get_page(p); \
+ } \
+ p; \
+})
+
static inline int remove_exclusive_swap_page(struct page *p)
{
return 0;
Index: linux-2.6.17-rc1-mm2/include/linux/swapops.h
===================================================================
--- linux-2.6.17-rc1-mm2.orig/include/linux/swapops.h 2006-04-13 16:43:10.000000000 -0700
+++ linux-2.6.17-rc1-mm2/include/linux/swapops.h 2006-04-14 09:55:25.000000000 -0700
@@ -77,7 +77,7 @@ static inline swp_entry_t make_migration

static inline int is_migration_entry(swp_entry_t entry)
{
- return swp_type(entry) == SWP_TYPE_MIGRATION;
+ return unlikely(swp_type(entry) == SWP_TYPE_MIGRATION);
}

static inline struct page *migration_entry_to_page(swp_entry_t entry)
-
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