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Subject: Re: [PATCH V4] mlx4_core: allocate ICM memory in page size chunks
To:     Qing Huang <qing.huang@oracle.com>, tariqt@mellanox.com,
        davem@davemloft.net, haakon.bugge@oracle.com, yanjun.zhu@oracle.com
Cc:     netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org, gi-oh.kim@profitbricks.com
References: <20180523232246.20445-1-qing.huang@oracle.com>
From:   Tariq Toukan <tariqt@mellanox.com>
Message-ID: <bc652655-29de-a34b-a78a-0de19fc20df5@mellanox.com>
Date:   Thu, 24 May 2018 12:45:03 +0300
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On 24/05/2018 2:22 AM, 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 kvzalloc to replace kcalloc which will fall back
> to vmalloc automatically if kmalloc fails.
> 
> Signed-off-by: Qing Huang <qing.huang@oracle.com>
> Acked-by: Daniel Jurgens <danielj@mellanox.com>
> Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.com>
> ---
> v4: use kvzalloc instead of vzalloc
>      add one err condition check
>      don't include vmalloc.h any more
> 
> v3: use PAGE_SIZE instead of PAGE_SHIFT
>      add comma to the end of enum variables
>      include vmalloc.h header file to avoid build issues on Sparc
> 
> v2: adjusted chunk size to reflect different architectures
> 
>   drivers/net/ethernet/mellanox/mlx4/icm.c | 16 +++++++++-------
>   1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx4/icm.c b/drivers/net/ethernet/mellanox/mlx4/icm.c
> index a822f7a..685337d 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	= PAGE_SIZE,
> +	MLX4_TABLE_CHUNK_SIZE	= PAGE_SIZE,
>   };
>   
>   static void mlx4_free_icm_pages(struct mlx4_dev *dev, struct mlx4_icm_chunk *chunk)
> @@ -398,9 +398,11 @@ int mlx4_init_icm_table(struct mlx4_dev *dev, struct mlx4_icm_table *table,
>   	u64 size;
>   
>   	obj_per_chunk = MLX4_TABLE_CHUNK_SIZE / obj_size;
> +	if (WARN_ON(!obj_per_chunk))
> +		return -EINVAL;
>   	num_icm = (nobj + obj_per_chunk - 1) / obj_per_chunk;
>   
> -	table->icm      = kcalloc(num_icm, sizeof(*table->icm), GFP_KERNEL);
> +	table->icm      = kvzalloc(num_icm * sizeof(*table->icm), GFP_KERNEL);
>   	if (!table->icm)
>   		return -ENOMEM;
>   	table->virt     = virt;
> @@ -446,7 +448,7 @@ 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);
> +	kvfree(table->icm);
>   
>   	return -ENOMEM;
>   }
> @@ -462,5 +464,5 @@ 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);
> +	kvfree(table->icm);
>   }
> 

Thanks Qing.

Reviewed-by: Tariq Toukan <tariqt@mellanox.com>