Docs/ABI/zram: document zram recompress sysfs knobs

Document zram re-compression sysfs knobs.

Link: https://lkml.kernel.org/r/20221115020314.386235-1-senozhatsky@chromium.orgSigned-off-by: NSergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: NMinchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

Documentation/ABI/testing/sysfs-block-zram

@@ -137,3 +137,17 @@ Description:
 		The writeback_limit file is read-write and specifies the maximum
 		amount of writeback ZRAM can do. The limit could be changed
 		in run time.
+
+What:		/sys/block/zram<id>/recomp_algorithm
+Date:		November 2022
+Contact:	Sergey Senozhatsky <senozhatsky@chromium.org>
+Description:
+		The recomp_algorithm file is read-write and allows to set
+		or show secondary compression algorithms.
+
+What:		/sys/block/zram<id>/recompress
+Date:		November 2022
+Contact:	Sergey Senozhatsky <senozhatsky@chromium.org>
+Description:
+		The recompress file is write-only and triggers re-compression
+		with secondary compression algorithms.