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Subject: Re: [PATCH] mlx4_core: allocate 4KB ICM chunks
To:     Qing Huang <qing.huang@oracle.com>, tariqt@mellanox.com,
        davem@davemloft.net
Cc:     netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20180510233143.7236-1-qing.huang@oracle.com>
From:   Yanjun Zhu <yanjun.zhu@oracle.com>
Organization: Oracle Corporation
Message-ID: <6454d5eb-2700-4fe2-fd91-d366112c4674@oracle.com>
Date:   Fri, 11 May 2018 08:13:35 +0800
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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?

Zhu Yanjun
> of DMA ops).
>
> Signed-off-by: Qing Huang <qing.huang@oracle.com>
> Acked-by: Daniel Jurgens <danielj@mellanox.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);
>   }