Re: [PATCH 3/4] scsi: ipr: use kmalloc() to allocate IPR dump buffer memory

[Wen Xiong <wenxiong@linux.ibm.com>]

On 2026-07-02 14:56, Brian King wrote:
> On 7/2/26 1:55 AM, Mike Rapoport wrote:
>> On Wed, Jul 01, 2026 at 04:03:48PM -0500, Brian King wrote:
>>> On 7/1/26 4:52 AM, Mike Rapoport wrote:
>>>> On Wed, Jul 01, 2026 at 09:03:06AM +0200, Hannes Reinecke wrote:
>>>>> On 6/30/26 12:54 PM, Mike Rapoport (Microsoft) wrote:
>>>>>> IPR dump machinery allocates memory to save adapter's crash dump 
>>>>>> using
>>>>>> __get_free_page().
>>>>>> 
>>>>>> This memory can be allocated with kmalloc() as there's nothing 
>>>>>> special
>>>>>> about it to go directly to the page allocator.
>>>>>> 
>>>>>> kmalloc() provides a better API that does not require ugly casts 
>>>>>> and
>>>>>> kfree() does not need to know the size of the freed object.
>>>>>> 
>>>>>> Replace use of __get_free_page() with kmalloc().
>>>>>> 
>>>>>> Link: 
>>>>>> https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
>>>>>> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>>>>>> ---
>>>>>>   drivers/scsi/ipr.c | 4 ++--
>>>>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>> 
>>>>>> diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
>>>>>> index d207e5e81afe..5a212bfdeec2 100644
>>>>>> --- a/drivers/scsi/ipr.c
>>>>>> +++ b/drivers/scsi/ipr.c
>>>>>> @@ -2893,7 +2893,7 @@ static int ipr_sdt_copy(struct ipr_ioa_cfg 
>>>>>> *ioa_cfg,
>>>>>>   	       (ioa_dump->hdr.len + bytes_copied) < max_dump_size) {
>>>>>>   		if (ioa_dump->page_offset >= PAGE_SIZE ||
>>>>>>   		    ioa_dump->page_offset == 0) {
>>>>>> -			page = (__be32 *)__get_free_page(GFP_ATOMIC);
>>>>>> +			page = kmalloc(PAGE_SIZE, GFP_ATOMIC);
>>>>>>   			if (!page) {
>>>>>>   				ipr_trace;
>>>>>> @@ -3226,7 +3226,7 @@ static void ipr_release_dump(struct kref 
>>>>>> *kref)
>>>>>>   	spin_unlock_irqrestore(ioa_cfg->host->host_lock, lock_flags);
>>>>>>   	for (i = 0; i < dump->ioa_dump.next_page_index; i++)
>>>>>> -		free_page((unsigned long) dump->ioa_dump.ioa_data[i]);
>>>>>> +		kfree(dump->ioa_dump.ioa_data[i]);
>>>>>>   	vfree(dump->ioa_dump.ioa_data);
>>>>>>   	kfree(dump);
>>>>>> 
>>>>> 
>>>>> I _think_ we can replace this with kvmalloc, and allocate the 
>>>>> entire
>>>>> dump buffer in one go. Once switched to kmalloc() it's kinda 
>>>>> pointless
>>>>> to allocate separate page-sized buffers here.
>>>> 
>>>> kmalloc() performance is on par with __get_free_page(), but 
>>>> kvmalloc()
>>>> would be slower if it falls back to vmalloc().
>>>> 
>>>> I'm not familiar with the driver to say if this could be an issue 
>>>> here.
>>> 
>>> This code only runs when the adapter has hit a fatal error, so should 
>>> be
>>> extremely rare. The memory is getting allocated while the storage 
>>> adapter
>>> is in a failed state, so anything running on the system at the time 
>>> could
>>> be stalled until recovery is completed. This memory is allocated and 
>>> should
>>> be freed soon after the adapter recovers. In order for this code to
>>> run, the iprdump daemon must be running, which will then read out the 
>>> dump
>>> after the adapter is recovered, and write it to disk, after which 
>>> time, the
>>> ipr driver will free the kernel memory.
>> 
>> Thanks for the explanation!
>> 
>> So the allocation is not on the hot path and it seems to me that
>> performance differences between kmalloc() and slower vmalloc() won't 
>> move a
>> needle relatively to the entire dump procedure.
>> 
>> And it seems that GFP_ATOMIC here is a historical artifact rather than
>> actual necessity. ipr_get_ioa_dump() runs in a workqueue context 
>> without
>> locks held so nothing warrants GFP_ATOMIC.
> 
> Agree that GFP_ATOMIC is not needed here, but we probably do need
> GFP_NOIO since we don't want these allocations starting I/O as the
> storage adapter is not in a state where it can handle I/O until
> the card is reset.
> 
> Thanks,
> 
> Brian

iprdump works with both of GFP_ATOMIC and GFP_NOIO.

Tested-by: Wen Xiong <wenxiong@linux.ibm.com>