Re: [PATCH for-next 3/3] RDMA/erdma: Remove unnecessary __GFP_ZERO flag

Boshi Yu
2024-03-13T02:40:10Z

On Tue, Mar 12, 2024 at 12:53:05PM +0200, Leon Romanovsky wrote:
> On Mon, Mar 11, 2024 at 07:38:21PM +0800, Boshi Yu wrote:
> > From: Boshi Yu <boshiyu@linux.alibaba.com>
> >
> > The dma_alloc_coherent() interface automatically zero the memory returned.
>
> Can you please point to the DMA code which does that?

We have noticed a patchset which ensures that dma_alloc_coherent() always
returns zeroed memory. The url of this patchset is listed as below:
https://lore.kernel.org/all/20181214082515.14835-1-hch@lst.de/T/#m70c723c646004445713f31b7837f7e9d910c06f5

Besides, you may refer to commit 518a2f1925c3 ("dma-mapping: zero memory returned from dma_alloc_*")
for details. This commit zeros memory by passing __GFP_ZERO flag or
calling memset internally. For example, the dma_alloc_direct() interface
calls memset() to zero the allocated memory.

Thanks,
Boshi Yu

>
> > Thus, we do not need to specify the __GFP_ZERO flag explicitly when we call
> > dma_alloc_coherent().
> >
> > Reviewed-by: Cheng Xu <chengyou@linux.alibaba.com>
> > Signed-off-by: Boshi Yu <boshiyu@linux.alibaba.com>
> > ---
> > drivers/infiniband/hw/erdma/erdma_cmdq.c | 6 ++----
> > drivers/infiniband/hw/erdma/erdma_eq.c | 6 ++----
> > 2 files changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/infiniband/hw/erdma/erdma_cmdq.c b/drivers/infiniband/hw/erdma/erdma_cmdq.c
> > index 0ac2683cfccf..43ff40b5a09d 100644
> > --- a/drivers/infiniband/hw/erdma/erdma_cmdq.c
> > +++ b/drivers/infiniband/hw/erdma/erdma_cmdq.c
> > @@ -127,8 +127,7 @@ static int erdma_cmdq_cq_init(struct erdma_dev *dev)
> >
> > cq->depth = cmdq->sq.depth;
> > cq->qbuf = dma_alloc_coherent(&dev->pdev->dev, cq->depth << CQE_SHIFT,
> > - &cq->qbuf_dma_addr,
> > - GFP_KERNEL | __GFP_ZERO);
> > + &cq->qbuf_dma_addr, GFP_KERNEL);
> > if (!cq->qbuf)
> > return -ENOMEM;
> >
> > @@ -162,8 +161,7 @@ static int erdma_cmdq_eq_init(struct erdma_dev *dev)
> >
> > eq->depth = cmdq->max_outstandings;
> > eq->qbuf = dma_alloc_coherent(&dev->pdev->dev, eq->depth << EQE_SHIFT,
> > - &eq->qbuf_dma_addr,
> > - GFP_KERNEL | __GFP_ZERO);
> > + &eq->qbuf_dma_addr, GFP_KERNEL);
> > if (!eq->qbuf)
> > return -ENOMEM;
> >
> > diff --git a/drivers/infiniband/hw/erdma/erdma_eq.c b/drivers/infiniband/hw/erdma/erdma_eq.c
> > index 0a4746e6d05c..84ccdd8144c9 100644
> > --- a/drivers/infiniband/hw/erdma/erdma_eq.c
> > +++ b/drivers/infiniband/hw/erdma/erdma_eq.c
> > @@ -87,8 +87,7 @@ int erdma_aeq_init(struct erdma_dev *dev)
> > eq->depth = ERDMA_DEFAULT_EQ_DEPTH;
> >
> > eq->qbuf = dma_alloc_coherent(&dev->pdev->dev, eq->depth << EQE_SHIFT,
> > - &eq->qbuf_dma_addr,
> > - GFP_KERNEL | __GFP_ZERO);
> > + &eq->qbuf_dma_addr, GFP_KERNEL);
> > if (!eq->qbuf)
> > return -ENOMEM;
> >
> > @@ -237,8 +236,7 @@ static int erdma_ceq_init_one(struct erdma_dev *dev, u16 ceqn)
> >
> > eq->depth = ERDMA_DEFAULT_EQ_DEPTH;
> > eq->qbuf = dma_alloc_coherent(&dev->pdev->dev, eq->depth << EQE_SHIFT,
> > - &eq->qbuf_dma_addr,
> > - GFP_KERNEL | __GFP_ZERO);
> > + &eq->qbuf_dma_addr, GFP_KERNEL);
> > if (!eq->qbuf)
> > return -ENOMEM;
> >
> > --
> > 2.39.3
> >
> >