[PATCHv5 12/13] zram: add incompressible writeback

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Add support for incompressible pages writeback:

  echo incompressible > /sys/block/zramX/writeback

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/admin-guide/blockdev/zram.rst |  7 ++++++-
 drivers/block/zram/zram_drv.c               | 18 ++++++++++++------
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index d898b7ace33d..f14c8c2e42f3 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -348,8 +348,13 @@ this can be accomplished with::
 
         echo huge_idle > /sys/block/zramX/writeback
 
+If a user chooses to writeback only incompressible pages (pages that none of
+algorithms can compress) this can be accomplished with::
+
+	echo incompressible > /sys/block/zramX/writeback
+
 If an admin wants to write a specific page in zram device to the backing device,
-they could write a page index into the interface.
+they could write a page index into the interface::
 
 	echo "page_index=1251" > /sys/block/zramX/writeback
 
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 89d25f60b33e..2e4ef1ba1973 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -648,10 +648,10 @@ 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<<0)
-#define IDLE_WRITEBACK (1<<1)
-
+#define PAGE_WRITEBACK			0
+#define HUGE_WRITEBACK			(1<<0)
+#define IDLE_WRITEBACK			(1<<1)
+#define INCOMPRESSIBLE_WRITEBACK	(1<<2)
 
 static ssize_t writeback_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
@@ -672,6 +672,8 @@ static ssize_t writeback_store(struct device *dev,
 		mode = HUGE_WRITEBACK;
 	else if (sysfs_streq(buf, "huge_idle"))
 		mode = IDLE_WRITEBACK | HUGE_WRITEBACK;
+	else if (sysfs_streq(buf, "incompressible"))
+		mode = INCOMPRESSIBLE_WRITEBACK;
 	else {
 		if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
 			return -EINVAL;
@@ -734,11 +736,15 @@ static ssize_t writeback_store(struct device *dev,
 			goto next;
 
 		if (mode & IDLE_WRITEBACK &&
-			  !zram_test_flag(zram, index, ZRAM_IDLE))
+		    !zram_test_flag(zram, index, ZRAM_IDLE))
 			goto next;
 		if (mode & HUGE_WRITEBACK &&
-			  !zram_test_flag(zram, index, ZRAM_HUGE))
+		    !zram_test_flag(zram, index, ZRAM_HUGE))
 			goto next;
+		if (mode & INCOMPRESSIBLE_WRITEBACK &&
+		    !zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+			goto next;
+
 		/*
 		 * Clearing ZRAM_UNDER_WB is duty of caller.
 		 * IOW, zram_free_page never clear it.
-- 
2.38.1.431.g37b22c650d-goog