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Subject[PATCH 2/3] slub: record page flag overlays explicitly
Date

SLUB reuses two page bits for internal purposes, it overlays PG_active
and PG_error. This is hidden away in slub.c. Document these overlays
explicitly in the main page-flags enum along with all the others.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
---
include/linux/page-flags.h | 7 +++++
mm/slub.c | 65 +++++++++++--------------------------------
2 files changed, 24 insertions(+), 48 deletions(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 2cc1fb1..dfd0a26 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -103,6 +103,10 @@ enum pageflags {

/* XEN */
PG_pinned = PG_owner_priv_1,
+
+ /* SLUB */
+ PG_slub_frozen = PG_active,
+ PG_slub_debug = PG_error,
};

#ifndef __GENERATING_BOUNDS_H
@@ -167,6 +171,9 @@ PAGEFLAG(Reserved, reserved) __CLEARPAGEFLAG(Reserved, reserved)
PAGEFLAG(Private, private) __CLEARPAGEFLAG(Private, private)
__SETPAGEFLAG(Private, private)

+__PAGEFLAG(SlubFrozen, slub_frozen)
+__PAGEFLAG(SlubDebug, slub_debug)
+
/*
* Only test-and-set exist for PG_writeback. The unconditional operators are
* risky: they bypass page accounting.
diff --git a/mm/slub.c b/mm/slub.c
index a505a82..c7f5653 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -102,44 +102,12 @@
* the fast path and disables lockless freelists.
*/

-#define FROZEN (1 << PG_active)
-
#ifdef CONFIG_SLUB_DEBUG
-#define SLABDEBUG (1 << PG_error)
+#define SLABDEBUG 1
#else
#define SLABDEBUG 0
#endif

-static inline int SlabFrozen(struct page *page)
-{
- return page->flags & FROZEN;
-}
-
-static inline void SetSlabFrozen(struct page *page)
-{
- page->flags |= FROZEN;
-}
-
-static inline void ClearSlabFrozen(struct page *page)
-{
- page->flags &= ~FROZEN;
-}
-
-static inline int SlabDebug(struct page *page)
-{
- return page->flags & SLABDEBUG;
-}
-
-static inline void SetSlabDebug(struct page *page)
-{
- page->flags |= SLABDEBUG;
-}
-
-static inline void ClearSlabDebug(struct page *page)
-{
- page->flags &= ~SLABDEBUG;
-}
-
/*
* Issues still to be resolved:
*
@@ -972,7 +940,7 @@ static int free_debug_processing(struct kmem_cache *s, struct page *page,
}

/* Special debug activities for freeing objects */
- if (!SlabFrozen(page) && !page->freelist)
+ if (!PageSlubFrozen(page) && !page->freelist)
remove_full(s, page);
if (s->flags & SLAB_STORE_USER)
set_track(s, object, TRACK_FREE, addr);
@@ -1158,7 +1126,7 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
page->flags |= 1 << PG_slab;
if (s->flags & (SLAB_DEBUG_FREE | SLAB_RED_ZONE | SLAB_POISON |
SLAB_STORE_USER | SLAB_TRACE))
- SetSlabDebug(page);
+ __SetPageSlubDebug(page);

start = page_address(page);

@@ -1185,14 +1153,14 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
int order = compound_order(page);
int pages = 1 << order;

- if (unlikely(SlabDebug(page))) {
+ if (unlikely(SLABDEBUG && PageSlubDebug(page))) {
void *p;

slab_pad_check(s, page);
for_each_object(p, s, page_address(page),
page->objects)
check_object(s, page, p, 0);
- ClearSlabDebug(page);
+ __ClearPageSlubDebug(page);
}

mod_zone_page_state(page_zone(page),
@@ -1289,7 +1257,7 @@ static inline int lock_and_freeze_slab(struct kmem_cache_node *n,
if (slab_trylock(page)) {
list_del(&page->lru);
n->nr_partial--;
- SetSlabFrozen(page);
+ __SetPageSlubFrozen(page);
return 1;
}
return 0;
@@ -1399,7 +1367,7 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail)
struct kmem_cache_node *n = get_node(s, page_to_nid(page));
struct kmem_cache_cpu *c = get_cpu_slab(s, smp_processor_id());

- ClearSlabFrozen(page);
+ __ClearPageSlubFrozen(page);
if (page->inuse) {

if (page->freelist) {
@@ -1407,7 +1375,8 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail)
stat(c, tail ? DEACTIVATE_TO_TAIL : DEACTIVATE_TO_HEAD);
} else {
stat(c, DEACTIVATE_FULL);
- if (SlabDebug(page) && (s->flags & SLAB_STORE_USER))
+ if (SLABDEBUG && PageSlubDebug(page) &&
+ (s->flags & SLAB_STORE_USER))
add_full(n, page);
}
slab_unlock(page);
@@ -1560,7 +1529,7 @@ load_freelist:
object = c->page->freelist;
if (unlikely(!object))
goto another_slab;
- if (unlikely(SlabDebug(c->page)))
+ if (unlikely(SLABDEBUG && PageSlubDebug(c->page)))
goto debug;

c->freelist = object[c->offset];
@@ -1597,7 +1566,7 @@ new_slab:
if (c->page)
flush_slab(s, c);
slab_lock(new);
- SetSlabFrozen(new);
+ __SetPageSlubFrozen(new);
c->page = new;
goto load_freelist;
}
@@ -1681,7 +1650,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
stat(c, FREE_SLOWPATH);
slab_lock(page);

- if (unlikely(SlabDebug(page)))
+ if (unlikely(SLABDEBUG && PageSlubDebug(page)))
goto debug;

checks_ok:
@@ -1689,7 +1658,7 @@ checks_ok:
page->freelist = object;
page->inuse--;

- if (unlikely(SlabFrozen(page))) {
+ if (unlikely(PageSlubFrozen(page))) {
stat(c, FREE_FROZEN);
goto out_unlock;
}
@@ -3314,12 +3283,12 @@ static void validate_slab_slab(struct kmem_cache *s, struct page *page,
s->name, page);

if (s->flags & DEBUG_DEFAULT_FLAGS) {
- if (!SlabDebug(page))
- printk(KERN_ERR "SLUB %s: SlabDebug not set "
+ if (!PageSlubDebug(page))
+ printk(KERN_ERR "SLUB %s: SlubDebug not set "
"on slab 0x%p\n", s->name, page);
} else {
- if (SlabDebug(page))
- printk(KERN_ERR "SLUB %s: SlabDebug set on "
+ if (PageSlubDebug(page))
+ printk(KERN_ERR "SLUB %s: SlubDebug set on "
"slab 0x%p\n", s->name, page);
}
}

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