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

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Message-Id: <5ABF1B88-882E-4575-8E8C-41F0452FECC1@oracle.com>
Date:   Fri, 11 May 2018 12:27:09 +0200
From:   Håkon Bugge <haakon.bugge@...cle.com>
To:     Qing Huang <qing.huang@...cle.com>
Cc:     tariqt@...lanox.com, davem@...emloft.net, netdev@...r.kernel.org,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mlx4_core: allocate 4KB ICM chunks



> On 11 May 2018, at 01:31, Qing Huang <qing.huang@...cle.com> 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
> 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

Shouldn’t these be the arch’s page size order? E.g., if running on SPARC, the hw page size is 8KiB.


Thxs, Håkon

> };
> 
> 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);
> }
> -- 
> 2.9.3
> 
> --
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