linux-kernel - Re: [PATCH] dma-remap: Use kvmalloc_array/kvfree for larger dma memory remap

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Message-ID: <CAJuCfpEMqLUePoqaQYKOK5OTFGHft8igg+NZ-R1qrudNJ5VmSg@mail.gmail.com>
Date:   Tue, 16 May 2023 12:41:56 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     gaoxu 00016977 <gaoxu2@...onor.com>
Cc:     "hch@....de" <hch@....de>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        yipengxiang 00013268 <yipengxiang@...onor.com>,
        wangbintian 00013160 <bintian.wang@...onor.com>,
        hanfeng 00012985 <feng.han@...onor.com>
Subject: Re: [PATCH] dma-remap: Use kvmalloc_array/kvfree for larger dma
 memory remap

On Sat, May 6, 2023 at 12:33 AM gaoxu 00016977 <gaoxu2@...onor.com> wrote:
>
> If dma_direct_alloc() alloc memory in size of 64MB, the inner function
> dma_common_contiguous_remap() will allocate 128KB memory by invoking
> the function kmalloc_array(). and the kmalloc_array seems to fail to try to
> allocate 128KB mem. work around by doing kvmalloc_array instead.

On systems like Android it's not unusual for order 5 allocation to
fail. The change seems safe to me with no downside since kvmalloc will
try kmalloc first.

>
> Signed-off-by: Gao Xu <gaoxu2@...onor.com>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

> ---
>  kernel/dma/remap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/dma/remap.c b/kernel/dma/remap.c index b45266680..27596f3b4 100644
> --- a/kernel/dma/remap.c
> +++ b/kernel/dma/remap.c
> @@ -43,13 +43,13 @@ void *dma_common_contiguous_remap(struct page *page, size_t size,
>         void *vaddr;
>         int i;
>
> -       pages = kmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
> +       pages = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
>         if (!pages)
>                 return NULL;
>         for (i = 0; i < count; i++)
>                 pages[i] = nth_page(page, i);
>         vaddr = vmap(pages, count, VM_DMA_COHERENT, prot);
> -       kfree(pages);
> +       kvfree(pages);
>
>         return vaddr;
>  }
> --
> 2.17.1
>