netdev - Re: [PATCH V2] mlx4_core: allocate ICM memory in page size chunks

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Date:   Mon, 14 May 2018 09:41:49 -0700
From:   Qing Huang <qing.huang@...cle.com>
To:     Tariq Toukan <ttoukan.linux@...il.com>, tariqt@...lanox.com,
        davem@...emloft.net, haakon.bugge@...cle.com, yanjun.zhu@...cle.com
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] mlx4_core: allocate ICM memory in page size chunks



On 5/13/2018 2:00 AM, Tariq Toukan wrote:
>
>
> On 11/05/2018 10:23 PM, 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 on x86_64 arch, the above issue is fixed.
>>
>> However in order to support smaller 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
>> of DMA ops).
>>
>> Signed-off-by: Qing Huang <qing.huang@...cle.com>
>> Acked-by: Daniel Jurgens <danielj@...lanox.com>
>> Reviewed-by: Zhu Yanjun <yanjun.zhu@...cle.com>
>> ---
>> v2 -> v1: adjusted chunk size to reflect different architectures.
>>
>>   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..ccb62b8 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 page size (default 4KB on many archs) 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 << PAGE_SHIFT,
>> +    MLX4_TABLE_CHUNK_SIZE    = 1 << PAGE_SHIFT
>
> Which is actually PAGE_SIZE.

Yes, we wanted to avoid high order memory allocations.

> Also, please add a comma at the end of the last entry.

Hmm..., followed the existing code style and checkpatch.pl didn't 
complain about the comma.

>
>>   };
>>     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));
>
> Why not kvzalloc ?

I think table->icm pointer array doesn't really need physically 
contiguous memory. Sometimes high order
memory allocation by kmalloc variants may trigger slow path and cause 
tasks to be blocked.

Thanks,
Qing

>
>>       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);
>>   }
>>
>
> Thanks for your patch.
>
> I need to verify there is no dramatic performance degradation here.
> You can prepare and send a v3 in the meanwhile.
>
> Thanks,
> Tariq
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