linux-kernel - Re: [PATCH for-next 4/6] RDMA/hns: Support flexible pagesize

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Date: Fri, 5 Jan 2024 13:55:11 +0800
From: Junxian Huang <huangjunxian6@...ilicon.com>
To: Jason Gunthorpe <jgg@...pe.ca>
CC: Leon Romanovsky <leon@...nel.org>, <linux-rdma@...r.kernel.org>,
	<linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH for-next 4/6] RDMA/hns: Support flexible pagesize



On 2024/1/5 4:29, Jason Gunthorpe wrote:
> On Tue, Dec 26, 2023 at 05:16:33PM +0800, Junxian Huang wrote:
>>
>>
>> On 2023/12/26 16:52, Leon Romanovsky wrote:
>>> On Mon, Dec 25, 2023 at 03:53:28PM +0800, Junxian Huang wrote:
>>>> From: Chengchang Tang <tangchengchang@...wei.com>
>>>>
>>>> In the current implementation, a fixed page size is used to
>>>> configure the PBL, which is not flexible enough and is not
>>>> conducive to the performance of the HW.
>>>>
>>>> Signed-off-by: Chengchang Tang <tangchengchang@...wei.com>
>>>> Signed-off-by: Junxian Huang <huangjunxian6@...ilicon.com>
>>>> ---
>>>>  drivers/infiniband/hw/hns/hns_roce_alloc.c  |   6 -
>>>>  drivers/infiniband/hw/hns/hns_roce_device.h |   9 ++
>>>>  drivers/infiniband/hw/hns/hns_roce_mr.c     | 168 +++++++++++++++-----
>>>>  3 files changed, 139 insertions(+), 44 deletions(-)
>>>
>>> I'm wonder if the ib_umem_find_best_pgsz() API should be used instead.
>>> What is missing there?
>>>
>>> Thanks
>>
>> Actually this API is used for umem.
>> For kmem, we add hns_roce_find_buf_best_pgsz() to do a similar job.
> 
> But why do you need to do something like this for kmem? It looked to
> me like kmem knows its allocation size when it was allocated, how come
> you need to iterate over all of it again?
> 
> Jason
> 

kmem was split into multiple small pages for allocation to prevent allocation
failure due to memory fragmentation.

And now we add this function to confirm whether these small pages have contiguous
address. If so, they can be combined into one huge page for use, which is more
likely when iommu/smmu is enabled.

Junxian