netdev - Re: [PATCH] mlx4_core: allocate 4KB ICM chunks

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Message-ID: <a1ecd591-7462-d43d-cc4e-206b0321742f@oracle.com>
Date:   Thu, 10 May 2018 18:36:58 -0700
From:   Qing Huang <qing.huang@...cle.com>
To:     Yanjun Zhu <yanjun.zhu@...cle.com>, tariqt@...lanox.com,
        davem@...emloft.net
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mlx4_core: allocate 4KB ICM chunks

Thank you for reviewing it!


On 5/10/2018 6:23 PM, Yanjun Zhu wrote:
>
>
>
> On 2018/5/11 9:15, Qing Huang wrote:
>>
>>
>>
>> On 5/10/2018 5:13 PM, Yanjun Zhu wrote:
>>>
>>>
>>> On 2018/5/11 7:31, Qing Huang wrote:
>>>> When a system is under memory presure (high usage with fragments),
>>>> the original 256KB ICM chunk allocations will likely trigger kernel
>>>> memory management to enter slow path doing memory compact/migration
>>>> ops in order to complete high order memory allocations.
>>>>
>>>> When that happens, user processes calling uverb APIs may get stuck
>>>> for more than 120s easily even though there are a lot of free pages
>>>> in smaller chunks available in the system.
>>>>
>>>> Syslog:
>>>> ...
>>>> Dec 10 09:04:51 slcc03db02 kernel: [397078.572732] INFO: task
>>>> oracle_205573_e:205573 blocked for more than 120 seconds.
>>>> ...
>>>>
>>>> With 4KB ICM chunk size, the above issue is fixed.
>>>>
>>>> However in order to support 4KB ICM chunk size, we need to fix another
>>>> issue in large size kcalloc allocations.
>>>>
>>>> E.g.
>>>> Setting log_num_mtt=30 requires 1G mtt entries. With the 4KB ICM chunk
>>>> size, each ICM chunk can only hold 512 mtt entries (8 bytes for 
>>>> each mtt
>>>> entry). So we need a 16MB allocation for a table->icm pointer array to
>>>> hold 2M pointers which can easily cause kcalloc to fail.
>>>>
>>>> The solution is to use vzalloc to replace kcalloc. There is no need
>>>> for contiguous memory pages for a driver meta data structure (no need
>>> Hi,
>>>
>>> Replace continuous memory pages with virtual memory, is there any 
>>> performance loss?
>>
>> Not really. "table->icm" will be accessed as individual pointer 
>> variables randomly. Kcalloc
>
> Sure. Thanks. If "table->icm" will be accessed as individual pointer 
> variables randomly, the performance loss
> caused by discontinuous memory will be very trivial.
>
> Reviewed-by: Zhu Yanjun <yanjun.zhu@...cle.com>
>
>> also returns a virtual address except its mapped pages are guaranteed 
>> to be contiguous
>> which will provide little advantage over vzalloc for individual 
>> pointer variable access.
>>
>> Qing
>>
>>>
>>> Zhu Yanjun
>>>> of DMA ops).
>>>>
>>>> Signed-off-by: Qing Huang <qing.huang@...cle.com>
>>>> Acked-by: Daniel Jurgens <danielj@...lanox.com>
>>>> ---
>>>>   drivers/net/ethernet/mellanox/mlx4/icm.c | 14 +++++++-------
>>>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/mellanox/mlx4/icm.c 
>>>> b/drivers/net/ethernet/mellanox/mlx4/icm.c
>>>> index a822f7a..2b17a4b 100644
>>>> --- a/drivers/net/ethernet/mellanox/mlx4/icm.c
>>>> +++ b/drivers/net/ethernet/mellanox/mlx4/icm.c
>>>> @@ -43,12 +43,12 @@
>>>>   #include "fw.h"
>>>>     /*
>>>> - * We allocate in as big chunks as we can, up to a maximum of 256 KB
>>>> - * per chunk.
>>>> + * We allocate in 4KB page size chunks to avoid high order memory
>>>> + * allocations in fragmented/high usage memory situation.
>>>>    */
>>>>   enum {
>>>> -    MLX4_ICM_ALLOC_SIZE    = 1 << 18,
>>>> -    MLX4_TABLE_CHUNK_SIZE    = 1 << 18
>>>> +    MLX4_ICM_ALLOC_SIZE    = 1 << 12,
>>>> +    MLX4_TABLE_CHUNK_SIZE    = 1 << 12
>>>>   };
>>>>     static void mlx4_free_icm_pages(struct mlx4_dev *dev, struct 
>>>> mlx4_icm_chunk *chunk)
>>>> @@ -400,7 +400,7 @@ int mlx4_init_icm_table(struct mlx4_dev *dev, 
>>>> struct mlx4_icm_table *table,
>>>>       obj_per_chunk = MLX4_TABLE_CHUNK_SIZE / obj_size;
>>>>       num_icm = (nobj + obj_per_chunk - 1) / obj_per_chunk;
>>>>   -    table->icm      = kcalloc(num_icm, sizeof(*table->icm), 
>>>> GFP_KERNEL);
>>>> +    table->icm      = vzalloc(num_icm * sizeof(*table->icm));
>>>>       if (!table->icm)
>>>>           return -ENOMEM;
>>>>       table->virt     = virt;
>>>> @@ -446,7 +446,7 @@ int mlx4_init_icm_table(struct mlx4_dev *dev, 
>>>> struct mlx4_icm_table *table,
>>>>               mlx4_free_icm(dev, table->icm[i], use_coherent);
>>>>           }
>>>>   -    kfree(table->icm);
>>>> +    vfree(table->icm);
>>>>         return -ENOMEM;
>>>>   }
>>>> @@ -462,5 +462,5 @@ void mlx4_cleanup_icm_table(struct mlx4_dev 
>>>> *dev, struct mlx4_icm_table *table)
>>>>               mlx4_free_icm(dev, table->icm[i], table->coherent);
>>>>           }
>>>>   -    kfree(table->icm);
>>>> +    vfree(table->icm);
>>>>   }
>>>
>>
>