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

[Qing Huang]

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.
> >
> > 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@xxxxxxxxxx>
> > Acked-by: Daniel Jurgens <danielj@xxxxxxxxxxxx>
> > Reviewed-by: Zhu Yanjun <yanjun.zhu@xxxxxxxxxx>
> > ---
> > v2 -> v1: adjusted chunk size to reflect different architectures.
> >
> > Â drivers/net/ethernet/mellanox/mlx4/icm.c | 14 +++++++-------
> > Â 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 @@
> > Â #include "fw.h"
> > Â Â /*
> > - * 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 */
> > Â enum {
> > -ÂÂÂ MLX4_ICM_ALLOC_SIZEÂÂÂ = 1 << 18,
> > -ÂÂÂ MLX4_TABLE_CHUNK_SIZEÂÂÂ = 1 << 18
> > +ÂÂÂ MLX4_ICM_ALLOC_SIZEÂÂÂ = 1 << PAGE_SHIFT,
> > +ÂÂÂ MLX4_TABLE_CHUNK_SIZEÂÂÂ = 1 << PAGE_SHIFT
>
> 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 checkpatch.pl didn't 
complain about the comma.

> > Â };
> > Â Â 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;
> > Â -ÂÂÂ table->icmÂÂÂÂÂ = 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.

Thanks,
Qing

> > ÂÂÂÂÂ if (!table->icm)
> > ÂÂÂÂÂÂÂÂÂ return -ENOMEM;
> > 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);
> > ÂÂÂÂÂÂÂÂÂ }
> > Â -ÂÂÂ kfree(table->icm);
> > +ÂÂÂ vfree(table->icm);
> > Â ÂÂÂÂÂ return -ENOMEM;
> > Â }
> > @@ -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);
> > ÂÂÂÂÂÂÂÂÂ }
> > Â -ÂÂÂ kfree(table->icm);
> > +ÂÂÂ vfree(table->icm);
> > Â }
>
> 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
> --
> To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html