[PATCH] zram: Introduce an aged idle interface

Brian Geffon
2021-09-17T21:07:07Z

This change introduces a new sysfs file for the zram idle interface.
The current idle interface has only a single mode "all." This is
severely limiting in that it requires that you have the foresight
to know that you'll want to have pages idle at some point in the future
and forces the user to mark everything as idle.

This new proposed file idle_aged takes a single integer argument which
represents the age of the pages (in seconds since access) to mark as idle.
Because it requires accessed tracking it is only enabled when
CONFIG_ZRAM_MEMORY_TRACKING is enabled. There are a few
reasons why this is being proposed as a new file rather than extending
the existing file. The first reason is that it wouldn't allow more code
sharing as this change already refactors the existing code to do so.
Secondly, having a standalone file allows a caller to quickly check if this
idle_aged interface is supported. Finally, it simplifies the parsing
logic because now you only need to parse an int rather than more complex
logic which would need to parse things like "aged 50."

Signed-off-by: Brian Geffon <bgeffon@google.com>
---
Documentation/admin-guide/blockdev/zram.rst | 11 ++-
drivers/block/zram/zram_drv.c | 75 +++++++++++++++++----
2 files changed, 70 insertions(+), 16 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index 700329d25f57..ecd1c4916a1c 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -209,6 +209,8 @@ compact WO trigger memory compaction
debug_stat RO this file is used for zram debugging purposes
backing_dev RW set up backend storage for zram to write out
idle WO mark allocated slot as idle
+idle_aged WO mark allocated slot older than 'age' seconds
+ as idle (see later)
====================== ====== ===============================================

@@ -325,8 +327,13 @@ as idle::

echo all > /sys/block/zramX/idle

-From now on, any pages on zram are idle pages. The idle mark
-will be removed until someone requests access of the block.
+Alternatively if the config option CONFIG_ZRAM_MEMORY_TRACKING is enabled
+the idle_aged interface can be used to mark only pages older than 'age'
+seconds as idle::
+
+ echo 86400 > /sys/block/zramX/idle_aged
+
+The idle mark will be removed until someone requests access of the block.
IOW, unless there is access request, those pages are still idle pages.

Admin can request writeback of those idle pages at right timing via::
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index fcaf2750f68f..a371dc0edf9d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -291,22 +291,16 @@ static ssize_t mem_used_max_store(struct device *dev,
return len;
}

-static ssize_t idle_store(struct device *dev,
- struct device_attribute *attr, const char *buf, size_t len)
+/*
+ * Mark all pages which are older than or equal to cutoff as IDLE.
+ * Callers should hold the zram init lock in read mode
+ **/
+static void mark_idle(struct zram *zram, ktime_t cutoff)
{
- struct zram *zram = dev_to_zram(dev);
+ int is_idle = 1;
unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
int index;

- if (!sysfs_streq(buf, "all"))
- return -EINVAL;
-
- down_read(&zram->init_lock);
- if (!init_done(zram)) {
- up_read(&zram->init_lock);
- return -EINVAL;
- }
-
for (index = 0; index < nr_pages; index++) {
/*
* Do not mark ZRAM_UNDER_WB slot as ZRAM_IDLE to close race.
@@ -314,16 +308,63 @@ static ssize_t idle_store(struct device *dev,
*/
zram_slot_lock(zram, index);
if (zram_allocated(zram, index) &&
- !zram_test_flag(zram, index, ZRAM_UNDER_WB))
- zram_set_flag(zram, index, ZRAM_IDLE);
+ !zram_test_flag(zram, index, ZRAM_UNDER_WB)) {
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+ is_idle = (!cutoff || cutoff >= zram->table[index].ac_time);
+#endif
+ if (is_idle)
+ zram_set_flag(zram, index, ZRAM_IDLE);
+ }
zram_slot_unlock(zram, index);
}
+}
+
+static ssize_t idle_store(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t len)
+{
+ struct zram *zram = dev_to_zram(dev);
+
+ if (!sysfs_streq(buf, "all"))
+ return -EINVAL;
+
+ down_read(&zram->init_lock);
+ if (!init_done(zram)) {
+ up_read(&zram->init_lock);
+ return -EINVAL;
+ }

+ /* Mark everything as idle */
+ mark_idle(zram, 0);
up_read(&zram->init_lock);

return len;
}

+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+static ssize_t idle_aged_store(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t len)
+{
+ struct zram *zram = dev_to_zram(dev);
+ ktime_t cutoff_time;
+ u64 age_sec;
+ ssize_t rv = -EINVAL;
+
+ down_read(&zram->init_lock);
+ if (!init_done(zram))
+ goto out;
+
+ if (kstrtoull(buf, 10, &age_sec))
+ goto out;
+
+ rv = len;
+ cutoff_time = ktime_sub(ktime_get_boottime(), ns_to_ktime(age_sec * NSEC_PER_SEC));
+ mark_idle(zram, cutoff_time);
+out:
+ up_read(&zram->init_lock);
+ return rv;
+}
+#endif
+
#ifdef CONFIG_ZRAM_WRITEBACK
static ssize_t writeback_limit_enable_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t len)
@@ -1840,6 +1881,9 @@ static DEVICE_ATTR_WO(reset);
static DEVICE_ATTR_WO(mem_limit);
static DEVICE_ATTR_WO(mem_used_max);
static DEVICE_ATTR_WO(idle);
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+static DEVICE_ATTR_WO(idle_aged);
+#endif
static DEVICE_ATTR_RW(max_comp_streams);
static DEVICE_ATTR_RW(comp_algorithm);
#ifdef CONFIG_ZRAM_WRITEBACK
@@ -1857,6 +1901,9 @@ static struct attribute *zram_disk_attrs[] = {
&dev_attr_mem_limit.attr,
&dev_attr_mem_used_max.attr,
&dev_attr_idle.attr,
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+ &dev_attr_idle_aged.attr,
+#endif
&dev_attr_max_comp_streams.attr,
&dev_attr_comp_algorithm.attr,
#ifdef CONFIG_ZRAM_WRITEBACK
--
2.33.0.464.g1972c5931b-goog