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SubjectRe: [slubllv6 07/17] slub: explicit list_lock taking
On Thu, 26 May 2011, David Rientjes wrote:

> > -static void add_full(struct kmem_cache_node *n, struct page *page)
> > +static void add_full(struct kmem_cache *s,
> > + struct kmem_cache_node *n, struct page *page)
>
> This also needs an update to the CONFIG_SLUB_DEBUG=n definition, not only
> for number of arguments but also the order:
>
> mm/slub.c:1781: error: too many arguments to function ‘add_full’
>
> and
>
> mm/slub.c:1781: warning: passing argument 1 of ‘add_full’ from incompatible pointer type
> mm/slub.c:1187: note: expected ‘struct kmem_cache_node *’ but argument is of type ‘struct kmem_cache *’
> mm/slub.c:1781: warning: passing argument 2 of ‘add_full’ from incompatible pointer type
> mm/slub.c:1187: note: expected ‘struct page *’ but argument is of type ‘struct kmem_cache_node *’

Correct.


Subject: slub: explicit list_lock taking

The allocator fastpath rework does change the usage of the list_lock.
Remove the list_lock processing from the functions that hide them from the
critical sections and move them into those critical sections.

This in turn simplifies the support functions (no __ variant needed anymore)
and simplifies the lock handling on bootstrap.

Inline add_partial since it becomes pretty simple.

Signed-off-by: Christoph Lameter <cl@linux.com>

---
mm/slub.c | 89 ++++++++++++++++++++++++++++++++++----------------------------
1 file changed, 49 insertions(+), 40 deletions(-)
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2011-05-31 10:14:00.812977367 -0500
+++ linux-2.6/mm/slub.c 2011-05-31 10:14:03.852977349 -0500
@@ -916,26 +916,27 @@ static inline void slab_free_hook(struct

/*
* Tracking of fully allocated slabs for debugging purposes.
+ *
+ * list_lock must be held.
*/
-static void add_full(struct kmem_cache_node *n, struct page *page)
+static void add_full(struct kmem_cache *s,
+ struct kmem_cache_node *n, struct page *page)
{
- spin_lock(&n->list_lock);
+ if (!(s->flags & SLAB_STORE_USER))
+ return;
+
list_add(&page->lru, &n->full);
- spin_unlock(&n->list_lock);
}

+/*
+ * list_lock must be held.
+ */
static void remove_full(struct kmem_cache *s, struct page *page)
{
- struct kmem_cache_node *n;
-
if (!(s->flags & SLAB_STORE_USER))
return;

- n = get_node(s, page_to_nid(page));
-
- spin_lock(&n->list_lock);
list_del(&page->lru);
- spin_unlock(&n->list_lock);
}

/* Tracking of the number of slabs for debugging purposes */
@@ -1060,8 +1061,13 @@ static noinline int free_debug_processin
}

/* Special debug activities for freeing objects */
- if (!page->frozen && !page->freelist)
+ if (!page->frozen && !page->freelist) {
+ struct kmem_cache_node *n = get_node(s, page_to_nid(page));
+
+ spin_lock(&n->list_lock);
remove_full(s, page);
+ spin_unlock(&n->list_lock);
+ }
if (s->flags & SLAB_STORE_USER)
set_track(s, object, TRACK_FREE, addr);
trace(s, page, object, 0);
@@ -1170,7 +1176,8 @@ static inline int slab_pad_check(struct
{ return 1; }
static inline int check_object(struct kmem_cache *s, struct page *page,
void *object, u8 val) { return 1; }
-static inline void add_full(struct kmem_cache_node *n, struct page *page) {}
+static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
+ struct page *page) {}
static inline unsigned long kmem_cache_flags(unsigned long objsize,
unsigned long flags, const char *name,
void (*ctor)(void *))
@@ -1420,38 +1427,33 @@ static __always_inline int slab_trylock(
}

/*
- * Management of partially allocated slabs
+ * Management of partially allocated slabs.
+ *
+ * list_lock must be held.
*/
-static void add_partial(struct kmem_cache_node *n,
+static inline void add_partial(struct kmem_cache_node *n,
struct page *page, int tail)
{
- spin_lock(&n->list_lock);
n->nr_partial++;
if (tail)
list_add_tail(&page->lru, &n->partial);
else
list_add(&page->lru, &n->partial);
- spin_unlock(&n->list_lock);
}

-static inline void __remove_partial(struct kmem_cache_node *n,
+/*
+ * list_lock must be held.
+ */
+static inline void remove_partial(struct kmem_cache_node *n,
struct page *page)
{
list_del(&page->lru);
n->nr_partial--;
}

-static void remove_partial(struct kmem_cache *s, struct page *page)
-{
- struct kmem_cache_node *n = get_node(s, page_to_nid(page));
-
- spin_lock(&n->list_lock);
- __remove_partial(n, page);
- spin_unlock(&n->list_lock);
-}
-
/*
- * Lock slab and remove from the partial list.
+ * Lock slab, remove from the partial list and put the object into the
+ * per cpu freelist.
*
* Must hold list_lock.
*/
@@ -1459,7 +1461,7 @@ static inline int lock_and_freeze_slab(s
struct page *page)
{
if (slab_trylock(page)) {
- __remove_partial(n, page);
+ remove_partial(n, page);
return 1;
}
return 0;
@@ -1576,12 +1578,17 @@ static void unfreeze_slab(struct kmem_ca
if (page->inuse) {

if (page->freelist) {
+ spin_lock(&n->list_lock);
add_partial(n, page, tail);
+ spin_unlock(&n->list_lock);
stat(s, tail ? DEACTIVATE_TO_TAIL : DEACTIVATE_TO_HEAD);
} else {
stat(s, DEACTIVATE_FULL);
- if (kmem_cache_debug(s) && (s->flags & SLAB_STORE_USER))
- add_full(n, page);
+ if (kmem_cache_debug(s) && (s->flags & SLAB_STORE_USER)) {
+ spin_lock(&n->list_lock);
+ add_full(s, n, page);
+ spin_unlock(&n->list_lock);
+ }
}
slab_unlock(page);
} else {
@@ -1597,7 +1604,9 @@ static void unfreeze_slab(struct kmem_ca
* kmem_cache_shrink can reclaim any empty slabs from
* the partial list.
*/
+ spin_lock(&n->list_lock);
add_partial(n, page, 1);
+ spin_unlock(&n->list_lock);
slab_unlock(page);
} else {
slab_unlock(page);
@@ -2099,7 +2108,11 @@ static void __slab_free(struct kmem_cach
* then add it.
*/
if (unlikely(!prior)) {
+ struct kmem_cache_node *n = get_node(s, page_to_nid(page));
+
+ spin_lock(&n->list_lock);
add_partial(get_node(s, page_to_nid(page)), page, 1);
+ spin_unlock(&n->list_lock);
stat(s, FREE_ADD_PARTIAL);
}

@@ -2113,7 +2126,11 @@ slab_empty:
/*
* Slab still on the partial list.
*/
- remove_partial(s, page);
+ struct kmem_cache_node *n = get_node(s, page_to_nid(page));
+
+ spin_lock(&n->list_lock);
+ remove_partial(n, page);
+ spin_unlock(&n->list_lock);
stat(s, FREE_REMOVE_PARTIAL);
}
slab_unlock(page);
@@ -2395,7 +2412,6 @@ static void early_kmem_cache_node_alloc(
{
struct page *page;
struct kmem_cache_node *n;
- unsigned long flags;

BUG_ON(kmem_cache_node->size < sizeof(struct kmem_cache_node));

@@ -2422,14 +2438,7 @@ static void early_kmem_cache_node_alloc(
init_kmem_cache_node(n, kmem_cache_node);
inc_slabs_node(kmem_cache_node, node, page->objects);

- /*
- * lockdep requires consistent irq usage for each lock
- * so even though there cannot be a race this early in
- * the boot sequence, we still disable irqs.
- */
- local_irq_save(flags);
add_partial(n, page, 0);
- local_irq_restore(flags);
}

static void free_kmem_cache_nodes(struct kmem_cache *s)
@@ -2713,7 +2722,7 @@ static void free_partial(struct kmem_cac
spin_lock_irqsave(&n->list_lock, flags);
list_for_each_entry_safe(page, h, &n->partial, lru) {
if (!page->inuse) {
- __remove_partial(n, page);
+ remove_partial(n, page);
discard_slab(s, page);
} else {
list_slab_objects(s, page,
@@ -3051,7 +3060,7 @@ int kmem_cache_shrink(struct kmem_cache
* may have freed the last object and be
* waiting to release the slab.
*/
- __remove_partial(n, page);
+ remove_partial(n, page);
slab_unlock(page);
discard_slab(s, page);
} else {
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