aboutsummaryrefslogtreecommitdiff
path: root/mm
diff options
context:
space:
mode:
Diffstat (limited to 'mm')
-rw-r--r--mm/slub.c154
1 files changed, 118 insertions, 36 deletions
diff --git a/mm/slub.c b/mm/slub.c
index bd2efae02bc..b07a1cab4f2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -81,10 +81,14 @@
* PageActive The slab is used as a cpu cache. Allocations
* may be performed from the slab. The slab is not
* on any slab list and cannot be moved onto one.
+ * The cpu slab may be equipped with an additioanl
+ * lockless_freelist that allows lockless access to
+ * free objects in addition to the regular freelist
+ * that requires the slab lock.
*
* PageError Slab requires special handling due to debug
* options set. This moves slab handling out of
- * the fast path.
+ * the fast path and disables lockless freelists.
*/
static inline int SlabDebug(struct page *page)
@@ -1014,6 +1018,7 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
set_freepointer(s, last, NULL);
page->freelist = start;
+ page->lockless_freelist = NULL;
page->inuse = 0;
out:
if (flags & __GFP_WAIT)
@@ -1276,6 +1281,23 @@ static void putback_slab(struct kmem_cache *s, struct page *page)
*/
static void deactivate_slab(struct kmem_cache *s, struct page *page, int cpu)
{
+ /*
+ * Merge cpu freelist into freelist. Typically we get here
+ * because both freelists are empty. So this is unlikely
+ * to occur.
+ */
+ while (unlikely(page->lockless_freelist)) {
+ void **object;
+
+ /* Retrieve object from cpu_freelist */
+ object = page->lockless_freelist;
+ page->lockless_freelist = page->lockless_freelist[page->offset];
+
+ /* And put onto the regular freelist */
+ object[page->offset] = page->freelist;
+ page->freelist = object;
+ page->inuse--;
+ }
s->cpu_slab[cpu] = NULL;
ClearPageActive(page);
@@ -1322,47 +1344,46 @@ static void flush_all(struct kmem_cache *s)
}
/*
- * slab_alloc is optimized to only modify two cachelines on the fast path
- * (aside from the stack):
+ * Slow path. The lockless freelist is empty or we need to perform
+ * debugging duties.
+ *
+ * Interrupts are disabled.
*
- * 1. The page struct
- * 2. The first cacheline of the object to be allocated.
+ * Processing is still very fast if new objects have been freed to the
+ * regular freelist. In that case we simply take over the regular freelist
+ * as the lockless freelist and zap the regular freelist.
*
- * The only other cache lines that are read (apart from code) is the
- * per cpu array in the kmem_cache struct.
+ * If that is not working then we fall back to the partial lists. We take the
+ * first element of the freelist as the object to allocate now and move the
+ * rest of the freelist to the lockless freelist.
*
- * Fastpath is not possible if we need to get a new slab or have
- * debugging enabled (which means all slabs are marked with SlabDebug)
+ * And if we were unable to get a new slab from the partial slab lists then
+ * we need to allocate a new slab. This is slowest path since we may sleep.
*/
-static void *slab_alloc(struct kmem_cache *s,
- gfp_t gfpflags, int node, void *addr)
+static void *__slab_alloc(struct kmem_cache *s,
+ gfp_t gfpflags, int node, void *addr, struct page *page)
{
- struct page *page;
void **object;
- unsigned long flags;
- int cpu;
+ int cpu = smp_processor_id();
- local_irq_save(flags);
- cpu = smp_processor_id();
- page = s->cpu_slab[cpu];
if (!page)
goto new_slab;
slab_lock(page);
if (unlikely(node != -1 && page_to_nid(page) != node))
goto another_slab;
-redo:
+load_freelist:
object = page->freelist;
if (unlikely(!object))
goto another_slab;
if (unlikely(SlabDebug(page)))
goto debug;
-have_object:
- page->inuse++;
- page->freelist = object[page->offset];
+ object = page->freelist;
+ page->lockless_freelist = object[page->offset];
+ page->inuse = s->objects;
+ page->freelist = NULL;
slab_unlock(page);
- local_irq_restore(flags);
return object;
another_slab:
@@ -1370,11 +1391,11 @@ another_slab:
new_slab:
page = get_partial(s, gfpflags, node);
- if (likely(page)) {
+ if (page) {
have_slab:
s->cpu_slab[cpu] = page;
SetPageActive(page);
- goto redo;
+ goto load_freelist;
}
page = new_slab(s, gfpflags, node);
@@ -1397,7 +1418,7 @@ have_slab:
discard_slab(s, page);
page = s->cpu_slab[cpu];
slab_lock(page);
- goto redo;
+ goto load_freelist;
}
/* New slab does not fit our expectations */
flush_slab(s, s->cpu_slab[cpu], cpu);
@@ -1405,16 +1426,52 @@ have_slab:
slab_lock(page);
goto have_slab;
}
- local_irq_restore(flags);
return NULL;
debug:
+ object = page->freelist;
if (!alloc_object_checks(s, page, object))
goto another_slab;
if (s->flags & SLAB_STORE_USER)
set_track(s, object, TRACK_ALLOC, addr);
trace(s, page, object, 1);
init_object(s, object, 1);
- goto have_object;
+
+ page->inuse++;
+ page->freelist = object[page->offset];
+ slab_unlock(page);
+ return object;
+}
+
+/*
+ * Inlined fastpath so that allocation functions (kmalloc, kmem_cache_alloc)
+ * have the fastpath folded into their functions. So no function call
+ * overhead for requests that can be satisfied on the fastpath.
+ *
+ * The fastpath works by first checking if the lockless freelist can be used.
+ * If not then __slab_alloc is called for slow processing.
+ *
+ * Otherwise we can simply pick the next object from the lockless free list.
+ */
+static void __always_inline *slab_alloc(struct kmem_cache *s,
+ gfp_t gfpflags, int node, void *addr)
+{
+ struct page *page;
+ void **object;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ page = s->cpu_slab[smp_processor_id()];
+ if (unlikely(!page || !page->lockless_freelist ||
+ (node != -1 && page_to_nid(page) != node)))
+
+ object = __slab_alloc(s, gfpflags, node, addr, page);
+
+ else {
+ object = page->lockless_freelist;
+ page->lockless_freelist = object[page->offset];
+ }
+ local_irq_restore(flags);
+ return object;
}
void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
@@ -1432,20 +1489,19 @@ EXPORT_SYMBOL(kmem_cache_alloc_node);
#endif
/*
- * The fastpath only writes the cacheline of the page struct and the first
- * cacheline of the object.
+ * Slow patch handling. This may still be called frequently since objects
+ * have a longer lifetime than the cpu slabs in most processing loads.
*
- * We read the cpu_slab cacheline to check if the slab is the per cpu
- * slab for this processor.
+ * So we still attempt to reduce cache line usage. Just take the slab
+ * lock and free the item. If there is no additional partial page
+ * handling required then we can return immediately.
*/
-static void slab_free(struct kmem_cache *s, struct page *page,
+static void __slab_free(struct kmem_cache *s, struct page *page,
void *x, void *addr)
{
void *prior;
void **object = (void *)x;
- unsigned long flags;
- local_irq_save(flags);
slab_lock(page);
if (unlikely(SlabDebug(page)))
@@ -1475,7 +1531,6 @@ checks_ok:
out_unlock:
slab_unlock(page);
- local_irq_restore(flags);
return;
slab_empty:
@@ -1487,7 +1542,6 @@ slab_empty:
slab_unlock(page);
discard_slab(s, page);
- local_irq_restore(flags);
return;
debug:
@@ -1502,6 +1556,34 @@ debug:
goto checks_ok;
}
+/*
+ * Fastpath with forced inlining to produce a kfree and kmem_cache_free that
+ * can perform fastpath freeing without additional function calls.
+ *
+ * The fastpath is only possible if we are freeing to the current cpu slab
+ * of this processor. This typically the case if we have just allocated
+ * the item before.
+ *
+ * If fastpath is not possible then fall back to __slab_free where we deal
+ * with all sorts of special processing.
+ */
+static void __always_inline slab_free(struct kmem_cache *s,
+ struct page *page, void *x, void *addr)
+{
+ void **object = (void *)x;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ if (likely(page == s->cpu_slab[smp_processor_id()] &&
+ !SlabDebug(page))) {
+ object[page->offset] = page->lockless_freelist;
+ page->lockless_freelist = object;
+ } else
+ __slab_free(s, page, x, addr);
+
+ local_irq_restore(flags);
+}
+
void kmem_cache_free(struct kmem_cache *s, void *x)
{
struct page *page;
generated by cgit v1.2.3 (git 2.25.1) at 2024-12-02 20:36:05 +0000