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SubjectRe: [PATCH V2] mlx4_core: allocate ICM memory in page size chunks
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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@oracle.com>
> Acked-by: Daniel Jurgens <danielj@mellanox.com>
> Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.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.
Also, please add a comma at the end of the last entry.

> };
>
> 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 ?

> 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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