From 0697212a411c1dae03c27845f2de2f3adb32c331 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Fri, 23 Jun 2006 02:03:35 -0700 Subject: [PATCH] Swapless page migration: add R/W migration entries Implement read/write migration ptes We take the upper two swapfiles for the two types of migration ptes and define a series of macros in swapops.h. The VM is modified to handle the migration entries. migration entries can only be encountered when the page they are pointing to is locked. This limits the number of places one has to fix. We also check in copy_pte_range and in mprotect_pte_range() for migration ptes. We check for migration ptes in do_swap_cache and call a function that will then wait on the page lock. This allows us to effectively stop all accesses to apge. Migration entries are created by try_to_unmap if called for migration and removed by local functions in migrate.c From: Hugh Dickins Several times while testing swapless page migration (I've no NUMA, just hacking it up to migrate recklessly while running load), I've hit the BUG_ON(!PageLocked(p)) in migration_entry_to_page. This comes from an orphaned migration entry, unrelated to the current correctly locked migration, but hit by remove_anon_migration_ptes as it checks an address in each vma of the anon_vma list. Such an orphan may be left behind if an earlier migration raced with fork: copy_one_pte can duplicate a migration entry from parent to child, after remove_anon_migration_ptes has checked the child vma, but before it has removed it from the parent vma. (If the process were later to fault on this orphaned entry, it would hit the same BUG from migration_entry_wait.) This could be fixed by locking anon_vma in copy_one_pte, but we'd rather not. There's no such problem with file pages, because vma_prio_tree_add adds child vma after parent vma, and the page table locking at each end is enough to serialize. Follow that example with anon_vma: add new vmas to the tail instead of the head. (There's no corresponding problem when inserting migration entries, because a missed pte will leave the page count and mapcount high, which is allowed for. And there's no corresponding problem when migrating via swap, because a leftover swap entry will be correctly faulted. But the swapless method has no refcounting of its entries.) From: Ingo Molnar pte_unmap_unlock() takes the pte pointer as an argument. From: Hugh Dickins Several times while testing swapless page migration, gcc has tried to exec a pointer instead of a string: smells like COW mappings are not being properly write-protected on fork. The protection in copy_one_pte looks very convincing, until at last you realize that the second arg to make_migration_entry is a boolean "write", and SWP_MIGRATION_READ is 30. Anyway, it's better done like in change_pte_range, using is_write_migration_entry and make_migration_entry_read. From: Hugh Dickins Remove unnecessary obfuscation from sys_swapon's range check on swap type, which blew up causing memory corruption once swapless migration made MAX_SWAPFILES no longer 2 ^ MAX_SWAPFILES_SHIFT. Signed-off-by: Hugh Dickins Acked-by: Martin Schwidefsky Signed-off-by: Hugh Dickins Signed-off-by: Christoph Lameter Signed-off-by: Ingo Molnar From: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 38 ++++++++++++++++++++++++-------------- 1 file changed, 24 insertions(+), 14 deletions(-) (limited to 'mm/rmap.c') diff --git a/mm/rmap.c b/mm/rmap.c index 10806b7af40c..3b8ce86daa3a 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -103,7 +103,7 @@ int anon_vma_prepare(struct vm_area_struct *vma) spin_lock(&mm->page_table_lock); if (likely(!vma->anon_vma)) { vma->anon_vma = anon_vma; - list_add(&vma->anon_vma_node, &anon_vma->head); + list_add_tail(&vma->anon_vma_node, &anon_vma->head); allocated = NULL; } spin_unlock(&mm->page_table_lock); @@ -127,7 +127,7 @@ void __anon_vma_link(struct vm_area_struct *vma) struct anon_vma *anon_vma = vma->anon_vma; if (anon_vma) { - list_add(&vma->anon_vma_node, &anon_vma->head); + list_add_tail(&vma->anon_vma_node, &anon_vma->head); validate_anon_vma(vma); } } @@ -138,7 +138,7 @@ void anon_vma_link(struct vm_area_struct *vma) if (anon_vma) { spin_lock(&anon_vma->lock); - list_add(&vma->anon_vma_node, &anon_vma->head); + list_add_tail(&vma->anon_vma_node, &anon_vma->head); validate_anon_vma(vma); spin_unlock(&anon_vma->lock); } @@ -620,17 +620,27 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, if (PageAnon(page)) { swp_entry_t entry = { .val = page_private(page) }; - /* - * Store the swap location in the pte. - * See handle_pte_fault() ... - */ - BUG_ON(!PageSwapCache(page)); - swap_duplicate(entry); - if (list_empty(&mm->mmlist)) { - spin_lock(&mmlist_lock); - if (list_empty(&mm->mmlist)) - list_add(&mm->mmlist, &init_mm.mmlist); - spin_unlock(&mmlist_lock); + + if (PageSwapCache(page)) { + /* + * Store the swap location in the pte. + * See handle_pte_fault() ... + */ + swap_duplicate(entry); + if (list_empty(&mm->mmlist)) { + spin_lock(&mmlist_lock); + if (list_empty(&mm->mmlist)) + list_add(&mm->mmlist, &init_mm.mmlist); + spin_unlock(&mmlist_lock); + } + } else { + /* + * Store the pfn of the page in a special migration + * pte. do_swap_page() will wait until the migration + * pte is removed and then restart fault handling. + */ + BUG_ON(!migration); + entry = make_migration_entry(page, pte_write(pteval)); } set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); BUG_ON(pte_file(*pte)); -- cgit v1.2.2