[patch 202/262] zram: introduce an aged idle interface

Andrew Morton
2021-11-05T20:45:21Z

From: Brian Geffon <bgeffon@google.com>
Subject: zram: introduce an aged idle interface

This change introduces an aged idle interface to the existing idle sysfs
file for zram.

When CONFIG_ZRAM_MEMORY_TRACKING is enabled the idle file now also accepts
an integer argument. This integer is the age (in seconds) of pages to
mark as idle. The idle file still supports 'all' as it always has. This
new approach allows for much more control over which pages get marked as
idle.

[bgeffon@google.com: use IS_ENABLED and cleanup comment]
Link: https://lkml.kernel.org/r/20210924161128.1508015-1-bgeffon@google.com
[bgeffon@google.com: Sergey's cleanup suggestions]
Link: https://lkml.kernel.org/r/20210929143056.13067-1-bgeffon@google.com
Link: https://lkml.kernel.org/r/20210923130115.1344361-1-bgeffon@google.com
Signed-off-by: Brian Geffon <bgeffon@google.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Jesse Barnes <jsbarnes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

Documentation/admin-guide/blockdev/zram.rst | 8 ++
drivers/block/zram/zram_drv.c | 62 +++++++++++++-----
2 files changed, 54 insertions(+), 16 deletions(-)

--- a/Documentation/admin-guide/blockdev/zram.rst~zram-introduce-an-aged-idle-interface
+++ a/Documentation/admin-guide/blockdev/zram.rst
@@ -328,6 +328,14 @@ as idle::
From now on, any pages on zram are idle pages. 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.
+Additionally, when CONFIG_ZRAM_MEMORY_TRACKING is enabled pages can be
+marked as idle based on how long (in seconds) it's been since they were
+last accessed::
+
+ echo 86400 > /sys/block/zramX/idle
+
+In this example all pages which haven't been accessed in more than 86400
+seconds (one day) will be marked idle.

Admin can request writeback of those idle pages at right timing via::

--- a/drivers/block/zram/zram_drv.c~zram-introduce-an-aged-idle-interface
+++ a/drivers/block/zram/zram_drv.c
@@ -291,22 +291,16 @@ static ssize_t mem_used_max_store(struct
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.
@@ -314,14 +308,50 @@ static ssize_t idle_store(struct device
*/
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 || ktime_after(cutoff, zram->table[index].ac_time);
+#endif
+ if (is_idle)
+ zram_set_flag(zram, index, ZRAM_IDLE);
+ }
zram_slot_unlock(zram, index);
}
+}

- up_read(&zram->init_lock);
+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);
+ ktime_t cutoff_time = 0;
+ ssize_t rv = -EINVAL;

- return len;
+ if (!sysfs_streq(buf, "all")) {
+ /*
+ * If it did not parse as 'all' try to treat it as an integer when
+ * we have memory tracking enabled.
+ */
+ u64 age_sec;
+
+ if (IS_ENABLED(CONFIG_ZRAM_MEMORY_TRACKING) && !kstrtoull(buf, 0, &age_sec))
+ cutoff_time = ktime_sub(ktime_get_boottime(),
+ ns_to_ktime(age_sec * NSEC_PER_SEC));
+ else
+ goto out;
+ }
+
+ down_read(&zram->init_lock);
+ if (!init_done(zram))
+ goto out_unlock;
+
+ /* A cutoff_time of 0 marks everything as idle, this is the "all" behavior */
+ mark_idle(zram, cutoff_time);
+ rv = len;
+
+out_unlock:
+ up_read(&zram->init_lock);
+out:
+ return rv;
}

#ifdef CONFIG_ZRAM_WRITEBACK
_