diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 13f1aa0..9c7fd988 100644
--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -297,6 +297,7 @@
    On ia64, 256M@256M is a generous value that typically works.
    The region may be automatically placed on ia64, see the
    dump-capture kernel config option notes above.
+   If use sparse memory, the size should be rounded to GRANULE boundaries.
 
    On s390x, typically use "crashkernel=xxM". The value of xx is dependent
    on the memory consumption of the kdump system. In general this is not