Re: [PATCH v4] zram: Implement multi-page write-back

Sergey Senozhatsky
2025-11-13T05:10:13Z

On (25/11/13 11:04), Sergey Senozhatsky wrote:
> On (25/11/06 09:49), Yuwen Chen wrote:
> > +
> > +#define ZRAM_WB_REQ_CNT (32)
> > +
>
> How was this number chosen? Did you try lower/higher values?
> I think we might want this to be runtime tunable via sysfs, e.g.
> writeback_batch_size attr, with min value of 1.

So I think something like this should work:

---
drivers/block/zram/zram_drv.c | 50 ++++++++++++++++++++++++++++++-----
drivers/block/zram/zram_drv.h | 1 +
2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 10b6e57603a0..cf92d4e8ca9b 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -570,6 +570,44 @@ static ssize_t writeback_limit_show(struct device *dev,
return sysfs_emit(buf, "%llu\n", val);
}

+static ssize_t writeback_batch_size_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t len)
+{
+ struct zram *zram = dev_to_zram(dev);
+ u32 val;
+ ssize_t ret = -EINVAL;
+
+ if (kstrtouint(buf, 10, &val))
+ return ret;
+
+ if (!val)
+ val = 1;
+
+ down_read(&zram->init_lock);
+ zram->wb_batch_size = val;
+ up_read(&zram->init_lock);
+ ret = len;
+
+ return ret;
+}
+
+static ssize_t writeback_batch_size_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ u32 val;
+ struct zram *zram = dev_to_zram(dev);
+
+ down_read(&zram->init_lock);
+ spin_lock(&zram->wb_limit_lock);
+ val = zram->wb_batch_size;
+ spin_unlock(&zram->wb_limit_lock);
+ up_read(&zram->init_lock);
+
+ return sysfs_emit(buf, "%u\n", val);
+}
+
static void reset_bdev(struct zram *zram)
{
if (!zram->backing_dev)
@@ -776,10 +814,7 @@ static void release_wb_ctl(struct zram_wb_ctl *wb_ctl)
kfree(wb_ctl);
}

-/* should be a module param */
-#define ZRAM_WB_REQ_CNT (32)
-
-static struct zram_wb_ctl *init_wb_ctl(void)
+static struct zram_wb_ctl *init_wb_ctl(struct zram *zram)
{
struct zram_wb_ctl *wb_ctl;
int i;
@@ -793,7 +828,7 @@ static struct zram_wb_ctl *init_wb_ctl(void)
atomic_set(&wb_ctl->num_inflight, 0);
init_completion(&wb_ctl->done);

- for (i = 0; i < ZRAM_WB_REQ_CNT; i++) {
+ for (i = 0; i < zram->wb_batch_size; i++) {
struct zram_wb_req *req;

req = kmalloc(sizeof(*req), GFP_KERNEL);
@@ -1145,7 +1180,7 @@ static ssize_t writeback_store(struct device *dev,
goto release_init_lock;
}

- wb_ctl = init_wb_ctl();
+ wb_ctl = init_wb_ctl(zram);
if (!wb_ctl) {
ret = -ENOMEM;
goto release_init_lock;
@@ -2786,6 +2821,7 @@ static DEVICE_ATTR_RW(backing_dev);
static DEVICE_ATTR_WO(writeback);
static DEVICE_ATTR_RW(writeback_limit);
static DEVICE_ATTR_RW(writeback_limit_enable);
+static DEVICE_ATTR_RW(writeback_batch_size);
#endif
#ifdef CONFIG_ZRAM_MULTI_COMP
static DEVICE_ATTR_RW(recomp_algorithm);
@@ -2807,6 +2843,7 @@ static struct attribute *zram_disk_attrs[] = {
&dev_attr_writeback.attr,
&dev_attr_writeback_limit.attr,
&dev_attr_writeback_limit_enable.attr,
+ &dev_attr_writeback_batch_size.attr,
#endif
&dev_attr_io_stat.attr,
&dev_attr_mm_stat.attr,
@@ -2868,6 +2905,7 @@ static int zram_add(void)

init_rwsem(&zram->init_lock);
#ifdef CONFIG_ZRAM_WRITEBACK
+ zram->wb_batch_size = 1;
spin_lock_init(&zram->wb_limit_lock);
#endif

diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 6cee93f9c0d0..1a647f42c1a4 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -129,6 +129,7 @@ struct zram {
struct file *backing_dev;
spinlock_t wb_limit_lock;
bool wb_limit_enable;
+ u32 wb_batch_size;
u64 bd_wb_limit;
struct block_device *bdev;
unsigned long *bitmap;
--
2.51.2.1041.gc1ab5b90ca-goog