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-rw-r--r--Documentation/powerpc/firmware-assisted-dump.txt17
1 files changed, 16 insertions, 1 deletions
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index bdd344aa18d9..18c5feef2577 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -113,7 +113,15 @@ header, is usually reserved at an offset greater than boot memory
size (see Fig. 1). This area is *not* released: this region will
be kept permanently reserved, so that it can act as a receptacle
for a copy of the boot memory content in addition to CPU state
-and HPTE region, in the case a crash does occur.
+and HPTE region, in the case a crash does occur. Since this reserved
+memory area is used only after the system crash, there is no point in
+blocking this significant chunk of memory from production kernel.
+Hence, the implementation uses the Linux kernel's Contiguous Memory
+Allocator (CMA) for memory reservation if CMA is configured for kernel.
+With CMA reservation this memory will be available for applications to
+use it, while kernel is prevented from using it. With this fadump will
+still be able to capture all of the kernel memory and most of the user
+space memory except the user pages that were present in CMA region.
o Memory Reservation during first kernel
@@ -162,6 +170,9 @@ How to enable firmware-assisted dump (fadump):
1. Set config option CONFIG_FA_DUMP=y and build kernel.
2. Boot into linux kernel with 'fadump=on' kernel cmdline option.
+ By default, fadump reserved memory will be initialized as CMA area.
+ Alternatively, user can boot linux kernel with 'fadump=nocma' to
+ prevent fadump to use CMA.
3. Optionally, user can also set 'crashkernel=' kernel cmdline
to specify size of the memory to reserve for boot memory dump
preservation.
@@ -172,6 +183,10 @@ NOTE: 1. 'fadump_reserve_mem=' parameter has been deprecated. Instead
2. If firmware-assisted dump fails to reserve memory then it
will fallback to existing kdump mechanism if 'crashkernel='
option is set at kernel cmdline.
+ 3. if user wants to capture all of user space memory and ok with
+ reserved memory not available to production system, then
+ 'fadump=nocma' kernel parameter can be used to fallback to
+ old behaviour.
Sysfs/debugfs files:
------------