btrfs-progs: check: adjust command line options for the low-memory mode

[platform/upstream/btrfs-progs.git] / Documentation / btrfs-check.asciidoc

diff --git a/Documentation/btrfs-check.asciidoc b/Documentation/btrfs-check.asciidoc
index 74a2ad2..abc9f0d 100644 (file)
--- a/Documentation/btrfs-check.asciidoc
+++ b/Documentation/btrfs-check.asciidoc
@@ -93,6 +93,19 @@ build the extent tree from scratch
 +
 NOTE: Do not use unless you know what you're doing.
 
+--mode=MODE::
+select mode of operation regarding memory and IO
++
+The 'MODE' can be one of 'original' and 'lowmem'. The original mode is mostly
+unoptimized regarding memory consumpption and can lead to out-of-memory
+conditions on large filesystems. The possible workaround is to export the block
+device over network to a machine with enough memory. The low memory mode is
+supposed to address the memory consumption, at the cost of increased IO when it
+needs to re-read blocks when needed. This may increase run time.
+
+NOTE: 'lowmem' mode does not work with '--repair' yet, and is still considered
+experimental.
+
 EXIT STATUS
 -----------
 *btrfs check* returns a zero exit status if it succeeds. Non zero is