[RFC 3/4] slub: Drop ->page field from kmem_cache_cpu

[Christoph Lameter]

Dropping the page field is possible since the page struct address
of an object or a freelist pointer can now always be calcualted from
the address. No freelist pointer will be NULL anymore so use
NULL to signify the condition that the current cpu has no
percpu slab attached to it.

Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>

Index: linux/include/linux/slub_def.h
===================================================================
--- linux.orig/include/linux/slub_def.h
+++ linux/include/linux/slub_def.h
@@ -40,7 +40,6 @@ enum stat_item {
 struct kmem_cache_cpu {
 	void **freelist;	/* Pointer to next available object */
 	unsigned long tid;	/* Globally unique transaction id */
-	struct page *page;	/* The slab from which we are allocating */
 	struct page *partial;	/* Partially allocated frozen slabs */
 #ifdef CONFIG_SLUB_STATS
 	unsigned stat[NR_SLUB_STAT_ITEMS];
Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c
+++ linux/mm/slub.c
@@ -1611,7 +1611,6 @@ static void *get_partial_node(struct kme
 
 		available += objects;
 		if (!object) {
-			c->page = page;
 			stat(s, ALLOC_FROM_PARTIAL);
 			object = t;
 		} else {
@@ -2049,10 +2048,9 @@ static void put_cpu_partial(struct kmem_
 static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
 {
 	stat(s, CPUSLAB_FLUSH);
-	deactivate_slab(s, c->page, c->freelist);
+	deactivate_slab(s, virt_to_head_page(c->freelist), c->freelist);
 
 	c->tid = next_tid(c->tid);
-	c->page = NULL;
 	c->freelist = NULL;
 }
 
@@ -2066,7 +2064,7 @@ static inline void __flush_cpu_slab(stru
 	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
 
 	if (likely(c)) {
-		if (c->page)
+		if (c->freelist)
 			flush_slab(s, c);
 
 		unfreeze_partials(s, c);
@@ -2085,7 +2083,7 @@ static bool has_cpu_slab(int cpu, void *
 	struct kmem_cache *s = info;
 	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
 
-	return c->page || c->partial;
+	return c->freelist || c->partial;
 }
 
 static void flush_all(struct kmem_cache *s)
@@ -2186,7 +2184,7 @@ static inline void *new_slab_objects(str
 	page = new_slab(s, flags, node);
 	if (page) {
 		c = raw_cpu_ptr(s->cpu_slab);
-		if (c->page)
+		if (c->freelist)
 			flush_slab(s, c);
 
 		/*
@@ -2197,7 +2195,6 @@ static inline void *new_slab_objects(str
 		page->freelist = end_token(freelist);
 
 		stat(s, ALLOC_SLAB);
-		c->page = page;
 		*pc = c;
 	} else
 		freelist = NULL;
@@ -2280,9 +2277,10 @@ static void *__slab_alloc(struct kmem_ca
 	c = this_cpu_ptr(s->cpu_slab);
 #endif
 
-	page = c->page;
-	if (!page)
+	if (!c->freelist || is_end_token(c->freelist))
 		goto new_slab;
+
+	page = virt_to_head_page(c->freelist);
 redo:
 
 	if (unlikely(!node_match(page, node))) {
@@ -2311,7 +2309,7 @@ redo:
 	freelist = get_freelist(s, page);
 
 	if (!freelist || is_end_token(freelist)) {
-		c->page = NULL;
+		c->freelist = NULL;
 		stat(s, DEACTIVATE_BYPASS);
 		goto new_slab;
 	}
@@ -2324,7 +2322,7 @@ load_freelist:
 	 * page is pointing to the page from which the objects are obtained.
 	 * That page must be frozen for per cpu allocations to work.
 	 */
-	VM_BUG_ON(!c->page->frozen);
+	VM_BUG_ON(!virt_to_head_page(freelist)->frozen);
 	c->freelist = get_freepointer(s, freelist);
 	c->tid = next_tid(c->tid);
 	local_irq_restore(flags);
@@ -2332,16 +2330,15 @@ load_freelist:
 
 deactivate:
 	deactivate_slab(s, page, c->freelist);
-	c->page = NULL;
 	c->freelist = NULL;
 
 new_slab:
 
 	if (c->partial) {
-		page = c->page = c->partial;
+		page = c->partial;
 		c->partial = page->next;
 		stat(s, CPU_PARTIAL_ALLOC);
-		c->freelist = NULL;
+		c->freelist = end_token(page_address(page));
 		goto redo;
 	}
 
@@ -2353,7 +2350,7 @@ new_slab:
 		return NULL;
 	}
 
-	page = c->page;
+	page = virt_to_head_page(freelist);
 	if (likely(!kmem_cache_debug(s) && pfmemalloc_match(page, gfpflags)))
 		goto load_freelist;
 
@@ -2363,7 +2360,6 @@ new_slab:
 		goto new_slab;	/* Slab failed checks. Next slab needed */
 
 	deactivate_slab(s, page, get_freepointer(s, freelist));
-	c->page = NULL;
 	c->freelist = NULL;
 	local_irq_restore(flags);
 	return freelist;
@@ -2384,7 +2380,6 @@ static __always_inline void *slab_alloc_
 {
 	void **object;
 	struct kmem_cache_cpu *c;
-	struct page *page;
 	unsigned long tid;
 
 	if (slab_pre_alloc_hook(s, gfpflags))
@@ -2416,8 +2411,7 @@ redo:
 	preempt_enable();
 
 	object = c->freelist;
-	page = c->page;
-	if (unlikely(!object || is_end_token(object) || !node_match(page, node))) {
+	if (unlikely(!object || is_end_token(object) || !node_match(virt_to_head_page(object), node))) {
 		object = __slab_alloc(s, gfpflags, node, addr, c);
 		stat(s, ALLOC_SLOWPATH);
 	} else {
@@ -2665,7 +2659,7 @@ redo:
 	tid = c->tid;
 	preempt_enable();
 
-	if (likely(page == c->page)) {
+	if (likely(c->freelist && page == virt_to_head_page(c->freelist))) {
 		set_freepointer(s, object, c->freelist);
 
 		if (unlikely(!this_cpu_cmpxchg_double(
@@ -4191,10 +4185,10 @@ static ssize_t show_slab_objects(struct
 			int node;
 			struct page *page;
 
-			page = ACCESS_ONCE(c->page);
-			if (!page)
+			if (!c->freelist)
 				continue;
 
+			page = virt_to_head_page(c->freelist);
 			node = page_to_nid(page);
 			if (flags & SO_TOTAL)
 				x = page->objects;

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