diff options
author | Christoph Lameter <clameter@sgi.com> | 2006-06-23 13:03:35 +0400 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-06-23 18:42:50 +0400 |
commit | 0697212a411c1dae03c27845f2de2f3adb32c331 (patch) | |
tree | 4bedcdb27522f4a42c422e0a8af155501f43a69c /include | |
parent | 8351a6e4785218a2b03c142be92926baff95ba5c (diff) | |
download | linux-0697212a411c1dae03c27845f2de2f3adb32c331.tar.xz |
[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 <hugh@veritas.com>
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 <mingo@elte.hu>
pte_unmap_unlock() takes the pte pointer as an argument.
From: Hugh Dickins <hugh@veritas.com>
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 <hugh@veritas.com>
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 <hugh@veritas.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Christoph Lameter <clameter@engr.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
From: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/swap.h | 7 | ||||
-rw-r--r-- | include/linux/swapops.h | 53 |
2 files changed, 60 insertions, 0 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h index cd28ad206dae..7cee73ef4f15 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -28,7 +28,14 @@ static inline int current_is_kswapd(void) * the type/offset into the pte as 5/27 as well. */ #define MAX_SWAPFILES_SHIFT 5 +#ifndef CONFIG_MIGRATION #define MAX_SWAPFILES (1 << MAX_SWAPFILES_SHIFT) +#else +/* Use last two entries for page migration swap entries */ +#define MAX_SWAPFILES ((1 << MAX_SWAPFILES_SHIFT)-2) +#define SWP_MIGRATION_READ MAX_SWAPFILES +#define SWP_MIGRATION_WRITE (MAX_SWAPFILES + 1) +#endif /* * Magic header for a swap area. The first part of the union is diff --git a/include/linux/swapops.h b/include/linux/swapops.h index 87b9d14c710d..ec639aa3a1d3 100644 --- a/include/linux/swapops.h +++ b/include/linux/swapops.h @@ -67,3 +67,56 @@ static inline pte_t swp_entry_to_pte(swp_entry_t entry) BUG_ON(pte_file(__swp_entry_to_pte(arch_entry))); return __swp_entry_to_pte(arch_entry); } + +#ifdef CONFIG_MIGRATION +static inline swp_entry_t make_migration_entry(struct page *page, int write) +{ + BUG_ON(!PageLocked(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_MIGRATION_READ || + swp_type(entry) == SWP_MIGRATION_WRITE); +} + +static inline int is_write_migration_entry(swp_entry_t entry) +{ + return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE); +} + +static inline struct page *migration_entry_to_page(swp_entry_t entry) +{ + struct page *p = pfn_to_page(swp_offset(entry)); + /* + * Any use of migration entries may only occur while the + * corresponding page is locked + */ + BUG_ON(!PageLocked(p)); + return p; +} + +static inline void make_migration_entry_read(swp_entry_t *entry) +{ + *entry = swp_entry(SWP_MIGRATION_READ, swp_offset(*entry)); +} + +extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd, + unsigned long address); +#else + +#define make_migration_entry(page, write) swp_entry(0, 0) +#define is_migration_entry(swp) 0 +#define migration_entry_to_page(swp) NULL +static inline void make_migration_entry_read(swp_entry_t *entryp) { } +static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd, + unsigned long address) { } +static inline int is_write_migration_entry(swp_entry_t entry) +{ + return 0; +} + +#endif + |