From 0d8359620d9be9823b6b9b3cf2dbe006cbfec594 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Mon, 14 Dec 2020 19:14:28 -0800
Subject: [PATCH] zram: support page writeback
There is demand to writeback specific process pages to backing store
instead of all idles pages in the system due to storage wear out concerns
and to launching latency of apps which are most of the time idle but are
critical for resume latency.
This patch extends the writeback knob to support a specific page
writeback.
Link: https://lkml.kernel.org/r/20201020190506.3758660-1-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
Documentation/admin-guide/blockdev/zram.rst | 5 +++++
drivers/block/zram/zram_drv.c | 21 +++++++++++++++++----
2 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index a6fd1f9b5faf5..8f3cfa42e443a 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -334,6 +334,11 @@ Admin can request writeback of those idle pages at right timing via::
With the command, zram writeback idle pages from memory to the storage.
+If admin want to write a specific page in zram device to backing device,
+they could write a page index into the interface.
+
+ echo "page_index=1251" > /sys/block/zramX/writeback
+
If there are lots of write IO with flash device, potentially, it has
flash wearout problem so that admin needs to design write limitation
to guarantee storage health for entire product life.
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 1b697208d6615..9a1e6ee4dbeff 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -620,15 +620,19 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
return 1;
}
+#define PAGE_WB_SIG "page_index="
+
+#define PAGE_WRITEBACK 0
#define HUGE_WRITEBACK 1
#define IDLE_WRITEBACK 2
+
static ssize_t writeback_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t len)
{
struct zram *zram = dev_to_zram(dev);
unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
- unsigned long index;
+ unsigned long index = 0;
struct bio bio;
struct bio_vec bio_vec;
struct page *page;
@@ -640,8 +644,17 @@ static ssize_t writeback_store(struct device *dev,
mode = IDLE_WRITEBACK;
else if (sysfs_streq(buf, "huge"))
mode = HUGE_WRITEBACK;
- else
- return -EINVAL;
+ else {
+ if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
+ return -EINVAL;
+
+ ret = kstrtol(buf + sizeof(PAGE_WB_SIG) - 1, 10, &index);
+ if (ret || index >= nr_pages)
+ return -EINVAL;
+
+ nr_pages = 1;
+ mode = PAGE_WRITEBACK;
+ }
down_read(&zram->init_lock);
if (!init_done(zram)) {
@@ -660,7 +673,7 @@ static ssize_t writeback_store(struct device *dev,
goto release_init_lock;
}
- for (index = 0; index < nr_pages; index++) {
+ while (nr_pages--) {
struct bio_vec bvec;
bvec.bv_page = page;
--
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