criu/plugin: Add environment variable to cap size of buffers.

The amdgpu plugin would create a memory buffer at the size
of the largest VRAM bo (buffer object). On some systems, VRAM
size exceeds RAM size, so the largest bo might be larger than
the available memory.

Add an environment variable KFD_MAX_BUFFER_SIZE, which caps the
size of this buffer. By default, it is set to 0, and has no
effect. When active, any bo larger than its value will be
saved to/restored from file in multiple passes.

Signed-off-by: David Francis <David.Francis@amd.com>

Documentation/criu-amdgpu-plugin.txt

@@ -97,6 +97,15 @@ executing criu command.
     E.g:
     KFD_CAPABILITY_CHECK=1
 
+*KFD_MAX_BUFFER_SIZE*::
+    On some systems, VRAM sizes may exceed RAM sizes, and so buffers for dumping
+    and restoring VRAM may be unable to fit. Set to a nonzero value (in bytes)
+    to set a limit on the plugin's memory usage.
+    Default:0 (Disabled)
+
+    E.g:
+    KFD_MAX_BUFFER_SIZE="2G"
+
 
 AUTHOR
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