[PATCH] zram: Add a huge_idle writeback mode

[Brian Geffon <bgeffon@google.com>]

Today it's only possible to write back as a page, idle, or huge.
A user might want to writeback pages which are huge and idle first
as these idle pages do not require decompression and make a good
first pass for writeback.

Signed-off-by: Brian Geffon <bgeffon@google.com>
---
 Documentation/admin-guide/blockdev/zram.rst |  6 ++++++
 drivers/block/zram/zram_drv.c               | 10 ++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index 3e11926a4df9..af1123bfaf92 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -343,6 +343,12 @@ Admin can request writeback of those idle pages at right timing via::
 
 With the command, zram writeback idle pages from memory to the storage.
 
+Additionally, if a user choose to writeback only huge and idle pages
+this can be accomplished with::
+
+        echo huge_idle > /sys/block/zramX/writeback
+
+
 If admin want to write a specific page in zram device to backing device,
 they could write a page index into the interface.
 
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index cb253d80d72b..f196902ae554 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -643,8 +643,8 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
 #define PAGE_WB_SIG "page_index="
 
 #define PAGE_WRITEBACK 0
-#define HUGE_WRITEBACK 1
-#define IDLE_WRITEBACK 2
+#define HUGE_WRITEBACK (1<<0)
+#define IDLE_WRITEBACK (1<<1)
 
 
 static ssize_t writeback_store(struct device *dev,
@@ -664,6 +664,8 @@ static ssize_t writeback_store(struct device *dev,
 		mode = IDLE_WRITEBACK;
 	else if (sysfs_streq(buf, "huge"))
 		mode = HUGE_WRITEBACK;
+	else if (sysfs_streq(buf, "huge_idle"))
+		mode = IDLE_WRITEBACK | HUGE_WRITEBACK;
 	else {
 		if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
 			return -EINVAL;
@@ -725,10 +727,10 @@ static ssize_t writeback_store(struct device *dev,
 				zram_test_flag(zram, index, ZRAM_UNDER_WB))
 			goto next;
 
-		if (mode == IDLE_WRITEBACK &&
+		if (mode & IDLE_WRITEBACK &&
 			  !zram_test_flag(zram, index, ZRAM_IDLE))
 			goto next;
-		if (mode == HUGE_WRITEBACK &&
+		if (mode & HUGE_WRITEBACK &&
 			  !zram_test_flag(zram, index, ZRAM_HUGE))
 			goto next;
 		/*
-- 
2.35.1.723.g4982287a31-goog