Adding ath/mhi and dma API developers to the discussion.
On 7/22/25 10:32 AM, Greg KH wrote:
> On Mon, Jul 21, 2025 at 06:13:10PM +0100, Matthew Wilcox wrote:
>> On Mon, Jul 21, 2025 at 08:03:12PM +0500, Muhammad Usama Anjum wrote:
>>> Hello,
>>>
>>> When 10-12GB our of total 16GB RAM is being used as page cache
>>> (active_file + inactive_file) at suspend time, the drivers fail to allocate
>>> dma memory at resume as dma memory is either occupied by the page cache or
>>> fragmented. Example:
>>>
>>> kworker/u33:5: page allocation failure: order:7, mode:0xc04(GFP_NOIO|GFP_DMA32), nodemask=(null),cpuset=/,mems_allowed=0
>>
>> Just to be clear, this is not a page cache problem. The driver is asking
>> us to do a 512kB allocation without doing I/O! This is a ridiculous
>> request that should be expected to fail.
>>
>> The solution, whatever it may be, is not related to the page cache.
>> I reject your diagnosis. Almost all of the page cache is clean and
>> could be dropped (as far as I can tell from the output below).
>>
>> Now, I'm not too familiar with how the page allocator chooses to fail
>> this request. Maybe it should be trying harder to drop bits of the page
>> cache. Maybe it should be doing some compaction.
That's very thoughtful. I'll look at the page allocator why isn't it dropping
cache or doing compaction.
>> I am not inclined to
>> go digging on your behalf, because frankly I'm offended by the suggestion
>> that the page cache is at fault.
I apologize—that wasn't my intention.
>>
>> Perhaps somebody else will help you, or you can dig into this yourself.
>
> I'm with Matthew, this really looks like a driver bug somehow. If there
> is page cache memory that is "clean", the driver should be able to
> access it just fine if really required.
>
> What exact driver(s) is having this problem? What is the exact error,
> and on what lines of code?
The issue occurs on both ath11k and mhi drivers during resume, when
dma_alloc_coherent(GFP_KERNEL) fails and returns -ENOMEM. This failure has
been observed at multiple points in these drivers.
For example, in the mhi driver, the failure is triggered when the
MHI's st_worker gets scheduled-in at resume.
mhi_pm_st_worker()
-> mhi_fw_load_handler()
-> mhi_load_image_bhi()
-> mhi_alloc_bhi_buffer()
-> dma_alloc_coherent(GFP_KERNEL) returns -ENOMEM
Thank you,
- Usama
