Re: [PATCH v2] lib: stackdepot: Add support to configure STACK_HASH_SIZE

[Vincenzo Frascino]

Hi Andrey,

On 12/3/20 4:15 PM, Andrey Konovalov wrote:
> On Thu, Dec 3, 2020 at 5:04 PM Qian Cai <qcai@xxxxxxxxxx> wrote:
>>
>> On Thu, 2020-11-26 at 10:13 +0530, vjitta@xxxxxxxxxxxxxx wrote:
>>> From: Yogesh Lal <ylal@xxxxxxxxxxxxxx>
>>>
>>> Add a kernel parameter stack_hash_order to configure STACK_HASH_SIZE.
>>>
>>> Aim is to have configurable value for STACK_HASH_SIZE, so that one
>>> can configure it depending on usecase there by reducing the static
>>> memory overhead.
>>>
>>> One example is of Page Owner, default value of STACK_HASH_SIZE lead
>>> stack depot to consume 8MB of static memory. Making it configurable
>>> and use lower value helps to enable features like CONFIG_PAGE_OWNER
>>> without any significant overhead.
>>>
>>> Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
>>> Signed-off-by: Yogesh Lal <ylal@xxxxxxxxxxxxxx>
>>> Signed-off-by: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
>>
>> Reverting this commit on today's linux-next fixed boot crash with KASAN.
>>
>> .config:
>> https://cailca.coding.net/public/linux/mm/git/files/master/x86.config
>> https://cailca.coding.net/public/linux/mm/git/files/master/arm64.config
> 
> Vincenzo, Catalin, looks like this is the cause of the crash you
> observed. Reverting this commit from next-20201203 fixes KASAN for me.
> 
> Thanks for the report Qian!
>

Thank you for this. I will try and let you know as well.

>>> ---
>>>  lib/stackdepot.c | 27 ++++++++++++++++++++++-----
>>>  1 file changed, 22 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
>>> index 81c69c0..ce53598 100644
>>> --- a/lib/stackdepot.c
>>> +++ b/lib/stackdepot.c
>>> @@ -141,14 +141,31 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
>>>       return stack;
>>>  }
>>>
>>> -#define STACK_HASH_ORDER 20
>>> -#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
>>> +static unsigned int stack_hash_order = 20;
>>> +#define STACK_HASH_SIZE (1L << stack_hash_order)
>>>  #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
>>>  #define STACK_HASH_SEED 0x9747b28c
>>>
>>> -static struct stack_record *stack_table[STACK_HASH_SIZE] = {
>>> -     [0 ...  STACK_HASH_SIZE - 1] = NULL
>>> -};
>>> +static struct stack_record **stack_table;
>>> +
>>> +static int __init setup_stack_hash_order(char *str)
>>> +{
>>> +     kstrtouint(str, 0, &stack_hash_order);
>>> +     return 0;
>>> +}
>>> +early_param("stack_hash_order", setup_stack_hash_order);
>>> +
>>> +static int __init init_stackdepot(void)
>>> +{
>>> +     int i;
>>> +
>>> +     stack_table = kvmalloc(sizeof(struct stack_record *) * STACK_HASH_SIZE, GFP_KERNEL);
>>> +     for (i = 0; i < STACK_HASH_SIZE; i++)
>>> +             stack_table[i] = NULL;
>>> +     return 0;
>>> +}
>>> +
>>> +early_initcall(init_stackdepot);
>>>
>>>  /* Calculate hash for a stack */
>>>  static inline u32 hash_stack(unsigned long *entries, unsigned int size)
>>
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-- 
Regards,
Vincenzo