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-rw-r--r--mm/migrate.c36
1 files changed, 10 insertions, 26 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 7b44ebdf2d26..08a7b6c4c266 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -819,6 +819,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
goto out_unlock;
wait_on_page_writeback(page);
}
+
/*
* By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
* we cannot notice that anon_vma is freed while we migrates a page.
@@ -826,34 +827,15 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
* of migration. File cache pages are no problem because of page_lock()
* File Caches may use write_page() or lock_page() in migration, then,
* just care Anon page here.
+ *
+ * Only page_get_anon_vma() understands the subtleties of
+ * getting a hold on an anon_vma from outside one of its mms.
+ * But if we cannot get anon_vma, then we won't need it anyway,
+ * because that implies that the anon page is no longer mapped
+ * (and cannot be remapped so long as we hold the page lock).
*/
- if (PageAnon(page) && !PageKsm(page)) {
- /*
- * Only page_lock_anon_vma_read() understands the subtleties of
- * getting a hold on an anon_vma from outside one of its mms.
- */
+ if (PageAnon(page) && !PageKsm(page))
anon_vma = page_get_anon_vma(page);
- if (anon_vma) {
- /*
- * Anon page
- */
- } else if (PageSwapCache(page)) {
- /*
- * We cannot be sure that the anon_vma of an unmapped
- * swapcache page is safe to use because we don't
- * know in advance if the VMA that this page belonged
- * to still exists. If the VMA and others sharing the
- * data have been freed, then the anon_vma could
- * already be invalid.
- *
- * To avoid this possibility, swapcache pages get
- * migrated but are not remapped when migration
- * completes
- */
- } else {
- goto out_unlock;
- }
- }
/*
* Block others from accessing the new page when we get around to
@@ -898,6 +880,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
}
} else if (page_mapped(page)) {
/* Establish migration ptes */
+ VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
+ page);
try_to_unmap(page,
TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
page_was_mapped = 1;