lkml.org 
[lkml]   [2013]   [Dec]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 02/23] mm/memblock: debug: don't free reserved array if !ARCH_DISCARD_MEMBLOCK
Hi Andrew,

On 12/10/2013 02:11 AM, Andrew Morton wrote:
> On Mon, 9 Dec 2013 16:50:35 -0500 Santosh Shilimkar <santosh.shilimkar@ti.com> wrote:
>
>> 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


\
 
 \ /
  Last update: 2013-12-10 17:01    [W:0.212 / U:0.560 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site