zram: move zram size warning to documentation

Move zram warning about disksize and size of memory correlation to zram
documentation.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 2eccddffa6c8..393541be1ec0 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -33,6 +33,11 @@ Following shows a typical sequence of steps for using zram.
             echo 512M > /sys/block/zram0/disksize
             echo 1G > /sys/block/zram0/disksize
 
+Note:
+There is little point creating a zram of greater than twice the size of memory
+since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
+size of the disk when not in use so a huge zram is wasteful.
+
 3) Activate:
         mkswap /dev/zram0
         swapon /dev/zram0