[PATCHv4 7/9] zram: add pages_per_pool_page device attribute

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Add a new sysfs knob that allows user-space to set
zsmalloc pages per-zspage limit value on per-device
basis.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 44 ++++++++++++++++++++++++++++++++++-
 drivers/block/zram/zram_drv.h |  2 ++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index bec02f636bce..cf9d3474b80c 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1180,6 +1180,45 @@ static ssize_t mm_stat_show(struct device *dev,
 	return ret;
 }
 
+static ssize_t pages_per_pool_page_show(struct device *dev,
+					struct device_attribute *attr,
+					char *buf)
+{
+	u32 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	val = zram->pages_per_pool_page;
+	up_read(&zram->init_lock);
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+
+static ssize_t pages_per_pool_page_store(struct device *dev,
+					 struct device_attribute *attr,
+					 const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	u32 val;
+
+	if (kstrtou32(buf, 10, &val))
+		return -EINVAL;
+
+	if (val < ZS_MIN_PAGES_PER_ZSPAGE || val > ZS_MAX_PAGES_PER_ZSPAGE)
+		return -EINVAL;
+
+	down_read(&zram->init_lock);
+	if (init_done(zram)) {
+		up_read(&zram->init_lock);
+		return -EINVAL;
+	}
+
+	zram->pages_per_pool_page = val;
+	up_read(&zram->init_lock);
+
+	return len;
+}
+
 #ifdef CONFIG_ZRAM_WRITEBACK
 #define FOUR_K(x) ((x) * (1 << (PAGE_SHIFT - 12)))
 static ssize_t bd_stat_show(struct device *dev,
@@ -1248,7 +1287,7 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 		return false;
 
 	zram->mem_pool = zs_create_pool(zram->disk->disk_name,
-					ZS_DEFAULT_PAGES_PER_ZSPAGE);
+					zram->pages_per_pool_page);
 	if (!zram->mem_pool) {
 		vfree(zram->table);
 		return false;
@@ -2174,6 +2213,7 @@ static DEVICE_ATTR_RW(writeback_limit_enable);
 static DEVICE_ATTR_RW(recomp_algorithm);
 static DEVICE_ATTR_WO(recompress);
 #endif
+static DEVICE_ATTR_RW(pages_per_pool_page);
 
 static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_disksize.attr,
@@ -2201,6 +2241,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_recomp_algorithm.attr,
 	&dev_attr_recompress.attr,
 #endif
+	&dev_attr_pages_per_pool_page.attr,
 	NULL,
 };
 
@@ -2238,6 +2279,7 @@ static int zram_add(void)
 		goto out_free_idr;
 	}
 
+	zram->pages_per_pool_page = ZS_DEFAULT_PAGES_PER_ZSPAGE;
 	zram->disk->major = zram_major;
 	zram->disk->first_minor = device_id;
 	zram->disk->minors = 1;
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 9d6fcfdf7aa7..bdfc9bf0bdd5 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -120,6 +120,8 @@ struct zram {
 	 */
 	u64 disksize;	/* bytes */
 	const char *comp_algs[ZRAM_MAX_ZCOMPS];
+
+	u32 pages_per_pool_page;
 	/*
 	 * Pages that compress to sizes equal or greater than this are stored
 	 * uncompressed in memory.
-- 
2.38.1.273.g43a17bfeac-goog