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

From: Qing Huang
Date: Mon May 14 2018 - 12:42:08 EST

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.

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.

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@xxxxxxxxxx>
Acked-by: Daniel Jurgens <danielj@xxxxxxxxxxxx>
Reviewed-by: Zhu Yanjun <yanjun.zhu@xxxxxxxxxx>
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.
ÂÂ */
 enum {

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 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,
ÂÂÂÂÂ obj_per_chunk = MLX4_TABLE_CHUNK_SIZE / obj_size;
ÂÂÂÂÂ num_icm = (nobj + obj_per_chunk - 1) / obj_per_chunk;
 - table->icm = kcalloc(num_icm, sizeof(*table->icm), GFP_KERNEL);
+ÂÂÂ table->icmÂÂÂÂÂ = 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.


ÂÂÂÂÂ if (!table->icm)
ÂÂÂÂÂ table->virtÂÂÂÂ = virt;
@@ -446,7 +446,7 @@ int mlx4_init_icm_table(struct mlx4_dev *dev, struct mlx4_icm_table *table,
ÂÂÂÂÂÂÂÂÂÂÂÂÂ mlx4_free_icm(dev, table->icm[i], use_coherent);
 - kfree(table->icm);
+ÂÂÂ vfree(table->icm);
 Â return -ENOMEM;
@@ -462,5 +462,5 @@ void mlx4_cleanup_icm_table(struct mlx4_dev *dev, struct mlx4_icm_table *table)
ÂÂÂÂÂÂÂÂÂÂÂÂÂ mlx4_free_icm(dev, table->icm[i], table->coherent);
 - kfree(table->icm);
+ÂÂÂ 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.

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