diff mbox

[v3,02/23] mm/memblock: debug: don't free reserved array if !ARCH_DISCARD_MEMBLOCK

Message ID 1386625856-12942-3-git-send-email-santosh.shilimkar@ti.com (mailing list archive)
State New, archived
Headers show

Commit Message

Santosh Shilimkar Dec. 9, 2013, 9:50 p.m. UTC 
From: Grygorii Strashko <grygorii.strashko@ti.com>

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).

Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>
Reviewed-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
---
 mm/memblock.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

Comments

Andrew Morton Dec. 10, 2013, 12:11 a.m. UTC | #1 
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.

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?
Grygorii Strashko Dec. 10, 2013, 4:44 p.m. UTC | #2 
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
diff mbox

Patch

diff --git a/mm/memblock.c b/mm/memblock.c
index aab5669..39855d4 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -265,6 +265,19 @@  phys_addr_t __init_memblock get_allocated_memblock_reserved_regions_info(
 	if (memblock.reserved.regions == memblock_reserved_init_regions)
 		return 0;
 
+	/*
+	 * Don't allow nobootmem allocator to free reserved memory regions
+	 * array if
+	 *  - CONFIG_DEBUG_FS is enabled;
+	 *  - CONFIG_ARCH_DISCARD_MEMBLOCK is not enabled;
+	 *  - reserved memory regions array have been resized during boot.
+	 * Otherwise debug_fs entry "sys/kernel/debug/memblock/reserved"
+	 * will show garbage instead of state of memory reservations.
+	 */
+	if (IS_ENABLED(CONFIG_DEBUG_FS) &&
+	    !IS_ENABLED(CONFIG_ARCH_DISCARD_MEMBLOCK))
+		return 0;
+
 	*addr = __pa(memblock.reserved.regions);
 
 	return PAGE_ALIGN(sizeof(struct memblock_region) *