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zram: use statically allocated compression algorithm names

PATCH Applied gao xu 1 participant 1 message Feb 26

Subsystems (2)
Block layer zram
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gao xu

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PATCH v2 1/1 zram: use statically allocated compression algorithm names

Currently, zram dynamically allocates memory for compressor algorithm names when they are set by the user. This requires careful memory management, including explicit kfree calls and special handling to avoid freeing statically defined default compressor names.

This patch refactors the way zram handles compression algorithm names. Instead of storing dynamically allocated copies, zram->comp_algs will now store pointers directly to the static name strings defined within the zcomp_ops backend structures, thereby removing the need for conditional kfree calls.

Signed-off-by gao xu <[email protected]>

---
v1 -> v2:
1. Remove compressor and pass buf directly to zcomp_lookup_backend_name().
2. Update the commit subject.
Based on Sergey Senozhatsky's suggestions.

https://lore.kernel.org/linux-block/[email protected]/T/#t

---
 drivers/block/zram/zcomp.c    |  9 +++++++--
 drivers/block/zram/zcomp.h    |  2 +-
 drivers/block/zram/zram_drv.c | 28 +++++-----------------------
 3 files changed, 13 insertions(+), 26 deletions(-)
drivers/block/zram/zcomp.c +7 -2
index a771a8ecc..974c46918 100644
@@ -84,9 +84,14 @@ static const struct zcomp_ops *lookup_backend_ops(const char *comp)
 	return backends[i];
 }
 
-bool zcomp_available_algorithm(const char *comp)
+const char *zcomp_lookup_backend_name(const char *comp)
 {
-	return lookup_backend_ops(comp) != NULL;
+	const struct zcomp_ops *backend = lookup_backend_ops(comp);
+
+	if (backend)
+		return backend->name;
+
+	return NULL;
 }
 
 /* show available compressors */
drivers/block/zram/zcomp.h +1 -1
index eacfd3f7d..81a0f3f6f 100644
@@ -80,7 +80,7 @@ struct zcomp {
 int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node);
 int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node);
 ssize_t zcomp_available_show(const char *comp, char *buf, ssize_t at);
-bool zcomp_available_algorithm(const char *comp);
+const char *zcomp_lookup_backend_name(const char *comp);
 
 struct zcomp *zcomp_create(const char *alg, struct zcomp_params *params);
 void zcomp_destroy(struct zcomp *comp);
drivers/block/zram/zram_drv.c +5 -23
index bca33403f..6f1ce0317 100644
@@ -1637,43 +1637,29 @@ static void zram_debugfs_unregister(struct zram *zram) {};
 
 static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg)
 {
-	/* Do not free statically defined compression algorithms */
-	if (zram->comp_algs[prio] != default_compressor)
-		kfree(zram->comp_algs[prio]);
-
 	zram->comp_algs[prio] = alg;
 }
 
 static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)
 {
-	char *compressor;
+	const char *alg;
 	size_t sz;
 
 	sz = strlen(buf);
 	if (sz >= ZRAM_MAX_ALGO_NAME_SZ)
 		return -E2BIG;
 
-	compressor = kstrdup(buf, GFP_KERNEL);
-	if (!compressor)
-		return -ENOMEM;
-
-	/* ignore trailing newline */
-	if (sz > 0 && compressor[sz - 1] == '\n')
-		compressor[sz - 1] = 0x00;
-
-	if (!zcomp_available_algorithm(compressor)) {
-		kfree(compressor);
+	alg = zcomp_lookup_backend_name(buf);
+	if (!alg)
 		return -EINVAL;
-	}
 
 	guard(rwsem_write)(&zram->dev_lock);
 	if (init_done(zram)) {
-		kfree(compressor);
 		pr_info("Can't change algorithm for initialized device\n");
 		return -EBUSY;
 	}
 
-	comp_algorithm_set(zram, prio, compressor);
+	comp_algorithm_set(zram, prio, alg);
 	return 0;
 }
 

@@ -2851,12 +2837,8 @@ static void zram_destroy_comps(struct zram *zram)
 		zram->num_active_comps--;
 	}
 
-	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
-		/* Do not free statically defined compression algorithms */
-		if (zram->comp_algs[prio] != default_compressor)
-			kfree(zram->comp_algs[prio]);
+	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++)
 		zram->comp_algs[prio] = NULL;
-	}
 
 	zram_comp_params_reset(zram);
 }

--