Re: [RFC] Order 4 allocation failures in the MEI client driver

[Rohit Agarwal <rohiagar@chromium.org>]

On 23/08/24 2:30 AM, Winkler, Tomas wrote:
>>>> On Wed, Aug 21, 2024, at 05:20, Rohit Agarwal wrote:
>>>>> On 19/08/24 6:45 PM, Arnd Bergmann wrote:
>>>>>> On Tue, Aug 13, 2024, at 10:45, Rohit Agarwal wrote:
>>>>>>
>>>>>> What is the call chain you see in the kernel messages? Is it
>>>>>> always the same?
>>>>> Yes the call stack is same everytime. This is the call stack
>>>>>
>>>>> <4>[ 2019.101352] dump_stack_lvl+0x69/0xa0 <4>[ 2019.101359]
>>>>> warn_alloc+0x10d/0x180 <4>[ 2019.101363]
>>>>> __alloc_pages_slowpath+0xe3d/0xe80
>>>>> <4>[ 2019.101366] __alloc_pages+0x22f/0x2b0 <4>[ 2019.101369]
>>>>> __kmalloc_large_node+0x9d/0x120 <4>[ 2019.101373] ?
>>>>> mei_cl_alloc_cb+0x34/0xa0 <4>[ 2019.101377] ?
>>>>> mei_cl_alloc_cb+0x74/0xa0 <4>[ 2019.101379] __kmalloc+0x86/0x130
>>>>> <4>[ 2019.101382] mei_cl_alloc_cb+0x74/0xa0 <4>[ 2019.101385]
>>>>> mei_cl_enqueue_ctrl_wr_cb+0x38/0x90
>>>> Ok, so this might be a result of mei_cl_enqueue_ctrl_wr_cb() doing
>>>>
>>>>          /* for RX always allocate at least client's mtu */
>>>>          if (length)
>>>>                  length = max_t(size_t, length, mei_cl_mtu(cl));
>>>>
>>>> which was added in 3030dc056459 ("mei: add wrapper for queuing
>>>> control commands."). All the callers seem to be passing a short
>>>> "length" of just a few bytes, but this would always extend it to
>>>> cl->me_cl->props.max_msg_length in mei_cl_mtu().
>>>>
>>>> Not sure where that part is set.
>>> It's allocating maximum header for receiving buffer so it can
>>> accommodate any response.
>>> Looks like this part can be optimized with pre allocated buffer pool.
>> I understand that it's always trying to allocate the maximum, the question is
>> whether there is ever a need to set the maximum to more than a page. Pre-
>> allocating a buffer at probe time would also address the issue, but if it's
>> possible to just make that buffer smaller, it wouldn't be needed.
>>
>> Is the 64KB buffer size part of the Chrome specific interface as well, or is that
>> part of the upstream kernel implementation?
> The upstream solution is for newer graphics cards and overall implementation is different.
> I'm trying to collect more information myself, it's summer vacation time, so it will take few days.
> Thanks
> Tomas
>
A gentle reminder.

Thanks,
Rohit.