[PATCHv7 24/24] zram: support priority parameter in recompression

[Sergey Senozhatsky]

recompress device attribute supports alg=NAME parameter
so that we can specify only one particular algorithm we
want to perform recompression with.  However, with algo
params we now can have several exactly same secondary
algorithms but each with its own params tuning (e.g.
priority 1 configured to use more aggressive level, and
priority 2 configured to use a pre-trained dictionary).
Support priority=NUM parameter so that we can correctly
determine which secondary algorithm we want to use.

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 Documentation/admin-guide/blockdev/zram.rst |  5 ++++-
 drivers/block/zram/zram_drv.c               | 12 ++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index bb52d2fc0587..bbb1b1b8f10e 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -512,11 +512,14 @@ registered compression algorithms, increases our chances of finding the
 algorithm that successfully compresses a particular page. Sometimes, however,
 it is convenient (and sometimes even necessary) to limit recompression to
 only one particular algorithm so that it will not try any other algorithms.
-This can be achieved by providing a algo=NAME parameter:::
+This can be achieved by providing a `algo` or `priority` parameter:::
 
 	#use zstd algorithm only (if registered)
 	echo "type=huge algo=zstd" > /sys/block/zramX/recompress
 
+	#use zstd algorithm only (if zstd was registered under priority 1)
+	echo "type=huge priority=1" > /sys/block/zramX/recompress
+
 memory tracking
 ===============
 
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9b29f9e6cb50..1f1bf175a6c3 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1855,6 +1855,18 @@ static ssize_t recompress_store(struct device *dev,
 			algo = val;
 			continue;
 		}
+
+		if (!strcmp(param, "priority")) {
+			ret = kstrtouint(val, 10, &prio);
+			if (ret)
+				return ret;
+
+			if (prio == ZRAM_PRIMARY_COMP)
+				prio = ZRAM_SECONDARY_COMP;
+
+			prio_max = min(prio + 1, ZRAM_MAX_COMPS);
+			continue;
+		}
 	}
 
 	if (threshold >= huge_class_size)
-- 
2.46.0.469.g59c65b2a67-goog