zram: Allocate struct zcomp_strm as per-CPU memory

zcomp::stream is a per-CPU pointer, pointing to struct zcomp_strm
which contains two pointers. Having struct zcomp_strm allocated
directly as per-CPU memory would avoid one additional memory
allocation and a pointer dereference. This also simplifies the
addition of a local_lock to struct zcomp_strm.

Allocate zcomp::stream directly as per-CPU memory.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-7-bigeasy@linutronix.de

drivers/block/zram/zcomp.c

@@ -37,19 +37,16 @@ static void zcomp_strm_free(struct zcomp_strm *zstrm)
 	if (!IS_ERR_OR_NULL(zstrm->tfm))
 		crypto_free_comp(zstrm->tfm);
 	free_pages((unsigned long)zstrm->buffer, 1);
-	kfree(zstrm);
+	zstrm->tfm = NULL;
+	zstrm->buffer = NULL;
 }
 
 /*
- * allocate new zcomp_strm structure with ->tfm initialized by
- * backend, return NULL on error
+ * Initialize zcomp_strm structure with ->tfm initialized by backend, and
+ * ->buffer. Return a negative value on error.
  */
-static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
+static int zcomp_strm_init(struct zcomp_strm *zstrm, struct zcomp *comp)
 {
-	struct zcomp_strm *zstrm = kmalloc(sizeof(*zstrm), GFP_KERNEL);
-	if (!zstrm)
-		return NULL;
-
 	zstrm->tfm = crypto_alloc_comp(comp->name, 0, 0);
 	/*
 	 * allocate 2 pages. 1 for compressed data, plus 1 extra for the
@@ -58,9 +55,9 @@ static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
 	zstrm->buffer = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
 	if (IS_ERR_OR_NULL(zstrm->tfm) || !zstrm->buffer) {
 		zcomp_strm_free(zstrm);
-		zstrm = NULL;
+		return -ENOMEM;
 	}
-	return zstrm;
+	return 0;
 }
 
 bool zcomp_available_algorithm(const char *comp)
@@ -113,7 +110,7 @@ ssize_t zcomp_available_show(const char *comp, char *buf)
 
 struct zcomp_strm *zcomp_stream_get(struct zcomp *comp)
 {
-	return *get_cpu_ptr(comp->stream);
+	return get_cpu_ptr(comp->stream);
 }
 
 void zcomp_stream_put(struct zcomp *comp)
@@ -159,36 +156,30 @@ int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
 {
 	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
 	struct zcomp_strm *zstrm;
+	int ret;
 
-	if (WARN_ON(*per_cpu_ptr(comp->stream, cpu)))
-		return 0;
-
-	zstrm = zcomp_strm_alloc(comp);
-	if (IS_ERR_OR_NULL(zstrm)) {
+	zstrm = per_cpu_ptr(comp->stream, cpu);
+	ret = zcomp_strm_init(zstrm, comp);
+	if (ret)
 		pr_err("Can't allocate a compression stream\n");
-		return -ENOMEM;
-	}
-	*per_cpu_ptr(comp->stream, cpu) = zstrm;
-	return 0;
+	return ret;
 }
 
 int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node)
 {
 	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
 	struct zcomp_strm *zstrm;
 
-	zstrm = *per_cpu_ptr(comp->stream, cpu);
-	if (!IS_ERR_OR_NULL(zstrm))
-		zcomp_strm_free(zstrm);
-	*per_cpu_ptr(comp->stream, cpu) = NULL;
+	zstrm = per_cpu_ptr(comp->stream, cpu);
+	zcomp_strm_free(zstrm);
 	return 0;
 }
 
 static int zcomp_init(struct zcomp *comp)
 {
 	int ret;
 
-	comp->stream = alloc_percpu(struct zcomp_strm *);
+	comp->stream = alloc_percpu(struct zcomp_strm);
 	if (!comp->stream)
 		return -ENOMEM;
 

drivers/block/zram/zcomp.h

@@ -14,7 +14,7 @@ struct zcomp_strm {
 
 /* dynamic per-device compression frontend */
 struct zcomp {
-	struct zcomp_strm * __percpu *stream;
+	struct zcomp_strm __percpu *stream;
 	const char *name;
 	struct hlist_node node;
 };