From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Make struct slab independent of struct page. It still uses the
underlying memory in struct page for storing slab-specific data,
but slab and slub can now be weaned off using struct page directly.
Some of the wrapper functions (slab_address() and slab_order())
still need to cast to struct folio, but this is a significant
disentanglement.
[ vbabka@xxxxxxx: Rebase on folios, use folio instead of page where possible.
Do not duplicate flags field in struct slab, instead make the related
accessors go through slab_folio(). For testing pfmemalloc use the
folio_*_active flag accessors directly so the PageSlabPfmemalloc wrappers can
be removed later.
Make folio_slab() expect only folio_test_slab() == true folios and
virt_to_slab() return NULL when folio_test_slab() == false.
Move struct slab to mm/slab.h.
Don't represent with struct slab pages that are not true slab pages, but
just a compound page obtained directly rom page allocator (with large
kmalloc() for SLUB and SLOB). ]
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
include/linux/mm_types.h | 10 +--
mm/slab.h | 167 +++++++++++++++++++++++++++++++++++++++
mm/slub.c | 8 +-
3 files changed, 176 insertions(+), 9 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c3a6e6209600..1ae3537c7920 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -56,11 +56,11 @@ struct mem_cgroup;
* in each subpage, but you may need to restore some of their values
* afterwards.
*
- * SLUB uses cmpxchg_double() to atomically update its freelist and
- * counters. That requires that freelist & counters be adjacent and
- * double-word aligned. We align all struct pages to double-word
- * boundaries, and ensure that 'freelist' is aligned within the
- * struct.
+ * SLUB uses cmpxchg_double() to atomically update its freelist and counters.
+ * That requires that freelist & counters in struct slab be adjacent and
+ * double-word aligned. Because struct slab currently just reinterprets the
+ * bits of struct page, we align all struct pages to double-word boundaries,
+ * and ensure that 'freelist' is aligned within struct slab.
*/
#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
#define _struct_page_alignment __aligned(2 * sizeof(unsigned long))
diff --git a/mm/slab.h b/mm/slab.h
index 56ad7eea3ddf..0e67a8cb7f80 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -5,6 +5,173 @@
* Internal slab definitions
*/
+/* Reuses the bits in struct page */
+struct slab {
+ unsigned long __page_flags;
+ union {
+ struct list_head slab_list;
+ struct { /* Partial pages */
+ struct slab *next;
+#ifdef CONFIG_64BIT
+ int slabs; /* Nr of slabs left */
+#else
+ short int slabs;
+#endif
+ };
+ struct rcu_head rcu_head;
+ };
+ struct kmem_cache *slab_cache; /* not slob */
+ /* Double-word boundary */
+ void *freelist; /* first free object */
+ union {
+ void *s_mem; /* slab: first object */
+ unsigned long counters; /* SLUB */
+ struct { /* SLUB */
+ unsigned inuse:16;
+ unsigned objects:15;
+ unsigned frozen:1;
+ };
+ };
+
+ union {
+ unsigned int active; /* SLAB */
+ int units; /* SLOB */
+ };
+ atomic_t __page_refcount;
+#ifdef CONFIG_MEMCG
+ unsigned long memcg_data;
+#endif
+};
+
+#define SLAB_MATCH(pg, sl) \
+ static_assert(offsetof(struct page, pg) == offsetof(struct slab, sl))
+SLAB_MATCH(flags, __page_flags);
+SLAB_MATCH(compound_head, slab_list); /* Ensure bit 0 is clear */
+SLAB_MATCH(slab_list, slab_list);
+SLAB_MATCH(rcu_head, rcu_head);
+SLAB_MATCH(slab_cache, slab_cache);
+SLAB_MATCH(s_mem, s_mem);
+SLAB_MATCH(active, active);
+SLAB_MATCH(_refcount, __page_refcount);
+#ifdef CONFIG_MEMCG
+SLAB_MATCH(memcg_data, memcg_data);
+#endif
+#undef SLAB_MATCH
+static_assert(sizeof(struct slab) <= sizeof(struct page));
+
+/**
+ * folio_slab - Converts from folio to slab.
+ * @folio: The folio.
+ *
+ * Currently struct slab is a different representation of a folio where
+ * folio_test_slab() is true.
+ *
+ * Return: The slab which contains this folio.
+ */
+#define folio_slab(folio) (_Generic((folio), \
+ const struct folio *: (const struct slab *)(folio), \
+ struct folio *: (struct slab *)(folio)))
+
+/**
+ * slab_folio - The folio allocated for a slab
+ * @slab: The slab.
+ *
+ * Slabs are allocated as folios that contain the individual objects and are
+ * using some fields in the first struct page of the folio - those fields are
+ * now accessed by struct slab. It is occasionally necessary to convert back to
+ * a folio in order to communicate with the rest of the mm. Please use this
+ * helper function instead of casting yourself, as the implementation may change
+ * in the future.
+ */
+#define slab_folio(s) (_Generic((s), \
+ const struct slab *: (const struct folio *)s, \
+ struct slab *: (struct folio *)s))
+
+/**
+ * page_slab - Converts from first struct page to slab.
+ * @p: The first (either head of compound or single) page of slab.
+ *
+ * A temporary wrapper to convert struct page to struct slab in situations where
+ * we know the page is the compound head, or single order-0 page.
+ *
+ * Long-term ideally everything would work with struct slab directly or go
+ * through folio to struct slab.
+ *
+ * Return: The slab which contains this page
+ */
+#define page_slab(p) (_Generic((p), \
+ const struct page *: (const struct slab *)(p), \
+ struct page *: (struct slab *)(p)))
+
+/**
+ * slab_page - The first struct page allocated for a slab
+ * @slab: The slab.
+ *
+ * A convenience wrapper for converting slab to the first struct page of the
+ * underlying folio, to communicate with code not yet converted to folio or
+ * struct slab.
+ */
+#define slab_page(s) folio_page(slab_folio(s), 0)
+
+/*
+ * If network-based swap is enabled, sl*b must keep track of whether pages
+ * were allocated from pfmemalloc reserves.
+ */
+static inline bool slab_test_pfmemalloc(const struct slab *slab)
+{
+ return folio_test_active((struct folio *)slab_folio(slab));
+}
+
+static inline void slab_set_pfmemalloc(struct slab *slab)
+{
+ folio_set_active(slab_folio(slab));
+}
+
+static inline void slab_clear_pfmemalloc(struct slab *slab)
+{
+ folio_clear_active(slab_folio(slab));
+}
+
+static inline void __slab_clear_pfmemalloc(struct slab *slab)
+{
+ __folio_clear_active(slab_folio(slab));
+}
+
+static inline void *slab_address(const struct slab *slab)
+{
+ return folio_address(slab_folio(slab));
+}
+
+static inline int slab_nid(const struct slab *slab)
+{
+ return folio_nid(slab_folio(slab));
+}
+
+static inline pg_data_t *slab_pgdat(const struct slab *slab)
+{
+ return folio_pgdat(slab_folio(slab));
+}
+
+static inline struct slab *virt_to_slab(const void *addr)
+{
+ struct folio *folio = virt_to_folio(addr);
+
+ if (!folio_test_slab(folio))
+ return NULL;
+
+ return folio_slab(folio);
+}
+
+static inline int slab_order(const struct slab *slab)
+{
+ return folio_order((struct folio *)slab_folio(slab));
+}
+
+static inline size_t slab_size(const struct slab *slab)
+{
+ return PAGE_SIZE << slab_order(slab);
+}
+
#ifdef CONFIG_SLOB
/*
* Common fields provided in kmem_cache by all slab allocators
diff --git a/mm/slub.c b/mm/slub.c
index 98bf50c1c145..4776bcc8c9e4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3787,7 +3787,7 @@ static unsigned int slub_min_objects;
* requested a higher minimum order then we start with that one instead of
* the smallest order which will fit the object.
*/
-static inline unsigned int slab_order(unsigned int size,
+static inline unsigned int calc_slab_order(unsigned int size,
unsigned int min_objects, unsigned int max_order,
unsigned int fract_leftover)
{
@@ -3851,7 +3851,7 @@ static inline int calculate_order(unsigned int size)
fraction = 16;
while (fraction >= 4) {
- order = slab_order(size, min_objects,
+ order = calc_slab_order(size, min_objects,
slub_max_order, fraction);
if (order <= slub_max_order)
return order;
@@ -3864,14 +3864,14 @@ static inline int calculate_order(unsigned int size)
* We were unable to place multiple objects in a slab. Now
* lets see if we can place a single object there.
*/
- order = slab_order(size, 1, slub_max_order, 1);
+ order = calc_slab_order(size, 1, slub_max_order, 1);
if (order <= slub_max_order)
return order;
/*
* Doh this slab cannot be placed using slub_max_order.
*/
- order = slab_order(size, 1, MAX_ORDER, 1);
+ order = calc_slab_order(size, 1, MAX_ORDER, 1);
if (order < MAX_ORDER)
return order;
return -ENOSYS;
--
2.33.1
