I cleaned up the patch a bit and ran some tests.
This patch implements the preservation of the write permissions.
The preservation of write permission avoids unnecessary COW operations
following page migration.
Signed-off-by: Christoph Lameter <[email protected]>
Signed-Off-By: KAMEZAWA Hiroyuki <[email protected]>
Index: linux-2.6.17-rc1-mm2/include/linux/swap.h
===================================================================
--- linux-2.6.17-rc1-mm2.orig/include/linux/swap.h 2006-04-14 09:08:42.000000000 -0700
+++ linux-2.6.17-rc1-mm2/include/linux/swap.h 2006-04-14 10:01:27.000000000 -0700
@@ -33,8 +33,9 @@ static inline int current_is_kswapd(void
#define MAX_SWAPFILES (1 << MAX_SWAPFILES_SHIFT)
#else
/* Use last entry for page migration swap entries */
-#define MAX_SWAPFILES ((1 << MAX_SWAPFILES_SHIFT)-1)
-#define SWP_TYPE_MIGRATION MAX_SWAPFILES
+#define MAX_SWAPFILES ((1 << MAX_SWAPFILES_SHIFT)-2)
+#define SWP_MIGRATION_READ MAX_SWAPFILES
+#define SWP_MIGRATION_WRITE (MAX_SWAPFILES + 1)
#endif
/*
Index: linux-2.6.17-rc1-mm2/include/linux/swapops.h
===================================================================
--- linux-2.6.17-rc1-mm2.orig/include/linux/swapops.h 2006-04-14 09:55:25.000000000 -0700
+++ linux-2.6.17-rc1-mm2/include/linux/swapops.h 2006-04-14 10:06:43.000000000 -0700
@@ -69,15 +69,22 @@ static inline pte_t swp_entry_to_pte(swp
}
#ifdef CONFIG_MIGRATION
-static inline swp_entry_t make_migration_entry(struct page *page)
+static inline swp_entry_t make_migration_entry(struct page *page, int write)
{
BUG_ON(!PageLocked(page));
- return swp_entry(SWP_TYPE_MIGRATION, page_to_pfn(page));
+ return swp_entry(write ? SWP_MIGRATION_WRITE : SWP_MIGRATION_READ,
+ page_to_pfn(page));
}
static inline int is_migration_entry(swp_entry_t entry)
{
- return unlikely(swp_type(entry) == SWP_TYPE_MIGRATION);
+ return unlikely(swp_type(entry) == SWP_MIGRATION_READ ||
+ swp_type(entry) == SWP_MIGRATION_WRITE);
+}
+
+static inline int is_write_migration_entry(swp_entry_t entry)
+{
+ return swp_type(entry) == SWP_MIGRATION_WRITE;
}
static inline struct page *migration_entry_to_page(swp_entry_t entry)
Index: linux-2.6.17-rc1-mm2/mm/rmap.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/rmap.c 2006-04-13 16:43:24.000000000 -0700
+++ linux-2.6.17-rc1-mm2/mm/rmap.c 2006-04-14 10:04:27.000000000 -0700
@@ -602,7 +602,7 @@ static int try_to_unmap_one(struct page
* pte is removed and then restart fault handling.
*/
BUG_ON(!migration);
- entry = make_migration_entry(page);
+ entry = make_migration_entry(page, pte_write(pteval));
}
set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
BUG_ON(pte_file(*pte));
Index: linux-2.6.17-rc1-mm2/mm/migrate.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/migrate.c 2006-04-13 16:44:07.000000000 -0700
+++ linux-2.6.17-rc1-mm2/mm/migrate.c 2006-04-14 10:06:01.000000000 -0700
@@ -167,7 +167,10 @@ static void remove_migration_pte(struct
inc_mm_counter(mm, anon_rss);
get_page(new);
- set_pte_at(mm, addr, ptep, pte_mkold(mk_pte(new, vma->vm_page_prot)));
+ pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
+ if (is_write_migration_entry(entry))
+ pte = pte_mkwrite(pte);
+ set_pte_at(mm, addr, ptep, pte);
page_add_anon_rmap(new, vma, addr);
out:
pte_unmap_unlock(pte, ptl);
-
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