[PATCH 3/8] Create sysfs nodes and export basic statistics

[Nitin Gupta <ngupta@vflare.org>]

Creates per-pool sysfs nodes: /sys/kernel/vm/zcache/pool<id>/
(<id> = 0, 1, 2, ...) to export following statistics:
 - orig_data_size: Uncompressed worth of data stored in the pool.
 - memlimit: Memory limit of the pool. This also allows changing
   it at runtime (default: 10% of RAM).

If memlimit is set to a value smaller than the current number
of page stored, then excess pages are not freed immediately but
further puts are blocked till sufficient number of pages are
flushed/freed.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
---
 drivers/staging/zram/zcache_drv.c |  132 ++++++++++++++++++++++++++++++++++++-
 drivers/staging/zram/zcache_drv.h |    8 ++
 2 files changed, 137 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/zram/zcache_drv.c b/drivers/staging/zram/zcache_drv.c
index 160c172..f680f19 100644
--- a/drivers/staging/zram/zcache_drv.c
+++ b/drivers/staging/zram/zcache_drv.c
@@ -440,6 +440,85 @@ static void zcache_free_inode_pages(struct zcache_inode_rb *znode)
 	} while (count == FREE_BATCH);
 }
 
+#ifdef CONFIG_SYSFS
+
+#define ZCACHE_POOL_ATTR_RO(_name) \
+	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+
+#define ZCACHE_POOL_ATTR(_name) \
+	static struct kobj_attribute _name##_attr = \
+		__ATTR(_name, 0644, _name##_show, _name##_store)
+
+static struct zcache_pool *zcache_kobj_to_pool(struct kobject *kobj)
+{
+	int i;
+
+	spin_lock(&zcache->pool_lock);
+	for (i = 0; i < MAX_ZCACHE_POOLS; i++)
+		if (zcache->pools[i]->kobj == kobj)
+			break;
+	spin_unlock(&zcache->pool_lock);
+
+	return zcache->pools[i];
+}
+
+static ssize_t orig_data_size_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	struct zcache_pool *zpool = zcache_kobj_to_pool(kobj);
+
+	return sprintf(buf, "%llu\n", zcache_get_stat(
+			zpool, ZPOOL_STAT_PAGES_STORED) << PAGE_SHIFT);
+}
+ZCACHE_POOL_ATTR_RO(orig_data_size);
+
+static void memlimit_sysfs_common(struct kobject *kobj, u64 *value, int store)
+{
+	struct zcache_pool *zpool = zcache_kobj_to_pool(kobj);
+
+	if (store)
+		zcache_set_memlimit(zpool, *value);
+	else
+		*value = zcache_get_memlimit(zpool);
+}
+
+static ssize_t memlimit_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t len)
+{
+	int ret;
+	u64 memlimit;
+
+	ret = strict_strtoull(buf, 10, &memlimit);
+	if (ret)
+		return ret;
+
+	memlimit &= PAGE_MASK;
+	memlimit_sysfs_common(kobj, &memlimit, 1);
+
+	return len;
+}
+
+static ssize_t memlimit_show(struct kobject *kobj,
+			struct kobj_attribute *attr, char *buf)
+{
+	u64 memlimit;
+
+	memlimit_sysfs_common(kobj, &memlimit, 0);
+	return sprintf(buf, "%llu\n", memlimit);
+}
+ZCACHE_POOL_ATTR(memlimit);
+
+static struct attribute *zcache_pool_attrs[] = {
+	&orig_data_size_attr.attr,
+	&memlimit_attr.attr,
+	NULL,
+};
+
+static struct attribute_group zcache_pool_attr_group = {
+	.attrs = zcache_pool_attrs,
+};
+#endif	/* CONFIG_SYSFS */
+
 /*
  * cleancache_ops.init_fs
  *
@@ -451,7 +530,8 @@ static void zcache_free_inode_pages(struct zcache_inode_rb *znode)
  */
 static int zcache_init_fs(size_t pagesize)
 {
-	int ret;
+	int ret, pool_id;
+	struct zcache_pool *zpool = NULL;
 
 	/*
 	 * pagesize parameter probably makes sense only for Xen's
@@ -469,14 +549,38 @@ static int zcache_init_fs(size_t pagesize)
 		goto out;
 	}
 
-	ret = zcache_create_pool();
-	if (ret < 0) {
+	pool_id = zcache_create_pool();
+	if (pool_id < 0) {
 		pr_info("Failed to create new pool\n");
 		ret = -ENOMEM;
 		goto out;
 	}
+	zpool = zcache->pools[pool_id];
+
+#ifdef CONFIG_SYSFS
+	snprintf(zpool->name, MAX_ZPOOL_NAME_LEN, "pool%d", pool_id);
+
+	/* Create /sys/kernel/mm/zcache/pool<id> (<id> = 0, 1, ...) */
+	zpool->kobj = kobject_create_and_add(zpool->name, zcache->kobj);
+	if (!zpool->kobj) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	/* Create various nodes under /sys/.../pool<id>/ */
+	ret = sysfs_create_group(zpool->kobj, &zcache_pool_attr_group);
+	if (ret) {
+		kobject_put(zpool->kobj);
+		goto out;
+	}
+#endif
+
+	ret = pool_id;	/* success */
 
 out:
+	if (ret < 0)	/* failure */
+		zcache_destroy_pool(zpool);
+
 	return ret;
 }
 
@@ -580,6 +684,13 @@ static void zcache_put_page(int pool_id, ino_t inode_no,
 	 */
 	zcache_inc_stat(zpool, ZPOOL_STAT_PAGES_STORED);
 
+	/*
+	 * memlimit can be changed any time by user using sysfs. If
+	 * it is set to a value smaller than current number of pages
+	 * stored, then excess pages are not freed immediately but
+	 * further puts are blocked till sufficient number of pages
+	 * are flushed/freed.
+	 */
 	if (zcache_get_stat(zpool, ZPOOL_STAT_PAGES_STORED) >
 			zcache_get_memlimit(zpool) >> PAGE_SHIFT) {
 		zcache_dec_stat(zpool, ZPOOL_STAT_PAGES_STORED);
@@ -690,6 +801,12 @@ static void zcache_flush_fs(int pool_id)
 	struct zcache_inode_rb *znode;
 	struct zcache_pool *zpool = zcache->pools[pool_id];
 
+#ifdef CONFIG_SYSFS
+	/* Remove per-pool sysfs entries */
+	sysfs_remove_group(zpool->kobj, &zcache_pool_attr_group);
+	kobject_put(zpool->kobj);
+#endif
+
 	/*
 	 * At this point, there is no active I/O on this filesystem.
 	 * So we can free all its pages without holding any locks.
@@ -722,6 +839,15 @@ static int __init zcache_init(void)
 	if (!zcache)
 		return -ENOMEM;
 
+#ifdef CONFIG_SYSFS
+	/* Create /sys/kernel/mm/zcache/ */
+	zcache->kobj = kobject_create_and_add("zcache", mm_kobj);
+	if (!zcache->kobj) {
+		kfree(zcache);
+		return -ENOMEM;
+	}
+#endif
+
 	spin_lock_init(&zcache->pool_lock);
 	cleancache_ops = ops;
 
diff --git a/drivers/staging/zram/zcache_drv.h b/drivers/staging/zram/zcache_drv.h
index bfba5d7..808cfb2 100644
--- a/drivers/staging/zram/zcache_drv.h
+++ b/drivers/staging/zram/zcache_drv.h
@@ -19,6 +19,7 @@
 #include <linux/types.h>
 
 #define MAX_ZCACHE_POOLS	32	/* arbitrary */
+#define MAX_ZPOOL_NAME_LEN	8	/* "pool"+id (shown in sysfs) */
 
 enum zcache_pool_stats_index {
 	ZPOOL_STAT_PAGES_STORED,
@@ -51,6 +52,10 @@ struct zcache_pool {
 	seqlock_t memlimit_lock;	/* protects memlimit */
 	u64 memlimit;			/* bytes */
 	struct zcache_pool_stats_cpu *stats;	/* percpu stats */
+#ifdef CONFIG_SYSFS
+	unsigned char name[MAX_ZPOOL_NAME_LEN];
+	struct kobject *kobj;		/* sysfs */
+#endif
 };
 
 /* Manage all zcache pools */
@@ -58,6 +63,9 @@ struct zcache {
 	struct zcache_pool *pools[MAX_ZCACHE_POOLS];
 	u32 num_pools;		/* current no. of zcache pools */
 	spinlock_t pool_lock;	/* protects pools[] and num_pools */
+#ifdef CONFIG_SYSFS
+	struct kobject *kobj;	/* sysfs */
+#endif
 };
 
 #endif
-- 
1.7.1.1

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