Hi Andrew,

On 12/10/2013 02:11 AM, Andrew Morton wrote:

On Mon, 9 Dec 2013 16:50:35 -0500 Santosh Shilimkar [off-list ref] wrote:

quoted

Now the Nobootmem allocator will always try to free memory allocated for
reserved memory regions (free_low_memory_core_early()) without taking
into to account current memblock debugging configuration
(CONFIG_ARCH_DISCARD_MEMBLOCK and CONFIG_DEBUG_FS state).
As result if:
  - CONFIG_DEBUG_FS defined
  - CONFIG_ARCH_DISCARD_MEMBLOCK not defined;
-  reserved memory regions array have been resized during boot

then:
- memory allocated for reserved memory regions array will be freed to
buddy allocator;
- debug_fs entry "sys/kernel/debug/memblock/reserved" will show garbage
instead of state of memory reservations. like:
    0: 0x98393bc0..0x9a393bbf
    1: 0xff120000..0xff11ffff
    2: 0x00000000..0xffffffff

Hence, do not free memory allocated for reserved memory regions if
defined(CONFIG_DEBUG_FS) && !defined(CONFIG_ARCH_DISCARD_MEMBLOCK).

Alternatives:

- disable /proc/sys/kernel/debug/memblock/reserved in this case

- disable defined(CONFIG_DEBUG_FS) &&
   !defined(CONFIG_ARCH_DISCARD_MEMBLOCK) in Kconfig.

Yes. But this is debug information and it's useful to have it.

How much memory are we talking about here?  If it's more than "very
little" then I think either of these would be better - most users will
value the extra memory over an accurate
/proc/sys/kernel/debug/memblock/reserved?

Sorry, I have no real statistic information and I hit this issue while testing this series
by simulating huge amount of bootmem allocation during kernel boot.
The real number of entries i saw on Keystone & OMAP boards is no more than ~20.

Few digits below:
- size of static reserved memory regions array is 2048 bytes
- the size of array is doubled during each allocation

Regards,
-grygorii