The patch titled
Wait for migrating page after incr of page count under anon_vma lock
has been removed from the -mm tree. Its filename is
wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock.patch
This patch was probably dropped from -mm because
it has now been merged into a subsystem tree or
into Linus's tree, or because it was folded into
its parent patch in the -mm tree.
From: Christoph Lameter <clameter@xxxxxxx>
Wait for migrating page after incr of page count under anon_vma lock
This patch replaces the yield() in do_swap_page with a call to
migration_entry_wait() in the migration code.
migration_entry_wait() locks the anonymous vma of the page and then safely
increments page count before waiting for the page to become unlocked.
Migration entries are only removed while holding the anon_vma lock
(See remove_migration_ptes). Therefore we can be sure that the
migration pte is not modified and the underlying page is not
removed while holding this lock.
Also make is_migration_entry() unlikely and clean up a unnecessary
BUG_ON.
Signed-off-by: Christoph Lameter <clameter@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
include/linux/swapops.h | 6 ++--
mm/memory.c | 4 +-
mm/migrate.c | 51 ++++++++++++++++++++++++++++++++++++++
3 files changed, 57 insertions(+), 4 deletions(-)
diff -puN include/linux/swapops.h~wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock include/linux/swapops.h
--- devel/include/linux/swapops.h~wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock 2006-04-14 23:06:35.000000000 -0700
+++ devel-akpm/include/linux/swapops.h 2006-04-14 23:06:35.000000000 -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)
@@ -88,14 +88,16 @@ static inline struct page *migration_ent
* corresponding page is locked
*/
BUG_ON(!PageLocked(p));
- BUG_ON(!is_migration_entry(entry));
return p;
}
+
+extern void migration_entry_wait(swp_entry_t, pte_t *);
#else
#define make_migration_entry(page) swp_entry(0, 0)
#define is_migration_entry(swp) 0
#define migration_entry_to_page(swp) NULL
+static inline void migration_entry_wait(swp_entry_t entry, pte_t *ptep) { }
#endif
diff -puN mm/memory.c~wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock mm/memory.c
--- devel/mm/memory.c~wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock 2006-04-14 23:06:35.000000000 -0700
+++ devel-akpm/mm/memory.c 2006-04-14 23:06:35.000000000 -0700
@@ -1880,8 +1880,8 @@ static int do_swap_page(struct mm_struct
entry = pte_to_swp_entry(orig_pte);
- if (unlikely(is_migration_entry(entry))) {
- yield();
+ if (is_migration_entry(entry)) {
+ migration_entry_wait(entry, page_table);
goto out;
}
diff -puN mm/migrate.c~wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock mm/migrate.c
--- devel/mm/migrate.c~wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock 2006-04-14 23:06:35.000000000 -0700
+++ devel-akpm/mm/migrate.c 2006-04-14 23:06:35.000000000 -0700
@@ -174,6 +174,57 @@ out:
}
/*
+ * Something used the pte of a page under migration. We need to
+ * get to the page and wait until migration is finished.
+ * When we return from this function the fault will be retried.
+ *
+ * This function is called from do_swap_page().
+ */
+void migration_entry_wait(swp_entry_t entry, pte_t *ptep)
+{
+ struct page *page = migration_entry_to_page(entry);
+ unsigned long mapping = (unsigned long)page->mapping;
+ struct anon_vma *anon_vma;
+ pte_t pte;
+
+ if (!mapping ||
+ (mapping & PAGE_MAPPING_ANON) == 0)
+ return;
+ /*
+ * We hold the mmap_sem lock.
+ */
+ anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
+
+ /*
+ * The anon_vma lock is also taken while removing the migration
+ * entries. Take the lock here to insure that the migration pte
+ * is not modified while we increment the page count.
+ * This is similar to find_get_page().
+ */
+ spin_lock(&anon_vma->lock);
+ pte = *ptep;
+ if (pte_present(pte) || pte_none(pte) || pte_file(pte)) {
+ spin_unlock(&anon_vma->lock);
+ return;
+ }
+ entry = pte_to_swp_entry(pte);
+ if (!is_migration_entry(entry) ||
+ migration_entry_to_page(entry) != page) {
+ /* Migration entry is gone */
+ spin_unlock(&anon_vma->lock);
+ return;
+ }
+ /* Pages with migration entries must be locked */
+ BUG_ON(!PageLocked(page));
+
+ /* Phew. Finally we can increment the refcount */
+ get_page(page);
+ spin_unlock(&anon_vma->lock);
+ wait_on_page_locked(page);
+ put_page(page);
+}
+
+/*
* Get rid of all migration entries and replace them by
* references to the indicated page.
*
_
Patches currently in -mm which might be from clameter@xxxxxxx are
origin.patch
page-migration-make-do_swap_page-redo-the-fault.patch
slab-extract-cache_free_alien-from-__cache_free.patch
migration-remove-unnecessary-pageswapcache-checks.patch
wait-for-migrating-page-after-incr-of-page-count-under-anon_vma-lock.patch
preserve-write-permissions-in-migration-entries.patch
migration_entry_wait-use-the-pte-lock-instead-of-the-anon_vma-lock.patch
read-write-migration-entries-implement-correct-behavior-in-copy_one_pte.patch
read-write-migration-entries-make-mprotect-convert-write-migration.patch
read-write-migration-entries-make-mprotect-convert-write-migration-fix.patch
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