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Diffstat (limited to 'Documentation/powerpc/firmware-assisted-dump.txt')
| -rw-r--r-- | Documentation/powerpc/firmware-assisted-dump.txt | 17 |
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: ------------ |