Re: [PATCH 2/7] dma-buf/udmabuf: account the page array metadata to memcg

[Christian König]

On 11/6/26 14:18, Tao Cui wrote:
> From: Tao Cui <cuitao@xxxxxxxxxx>
> 
> udmabuf pins the pages of a memfd and hands them out as a dma-buf.  The
> data pages keep the accounting of the memfd they were instantiated in,
> but the bookkeeping around them does not: the page pointer array and
> the pinned_folios array, both sized by the buffer page count, plus the
> transient folios array sized by the memfd folio count, are plain
> GFP_KERNEL.  A 1GB buffer costs about 4MB of uncharged SUnreclaim
> memory, and size_limit_mb defaults to INT_MAX.
> 
> Charge the three kvmalloc allocations so the creator pays for the
> metadata it induces.  The system heap in the same subsystem already
> accounts its buffer allocation; the data pages here stay with the
> memfd.

T.J. needs to take a look here, but I fear that this might break uAPI.

A lot of the DMA-buf resources are intentionally not charged against memcg.

Regards,
Christian.

> 
> Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>
> ---
>  drivers/dma-buf/udmabuf.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index df6dd0046242..40182c82df6b 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -190,11 +190,12 @@ static void unpin_all_folios(struct udmabuf *ubuf)
> 
>  static __always_inline int init_udmabuf(struct udmabuf *ubuf, pgoff_t pgcnt)
>  {
> -       ubuf->pages = kvmalloc_objs(*ubuf->pages, pgcnt);
> +       ubuf->pages = kvmalloc_objs(*ubuf->pages, pgcnt, GFP_KERNEL_ACCOUNT);
>         if (!ubuf->pages)
>                 return -ENOMEM;
> 
> -       ubuf->pinned_folios = kvmalloc_objs(*ubuf->pinned_folios, pgcnt);
> +       ubuf->pinned_folios = kvmalloc_objs(*ubuf->pinned_folios, pgcnt,
> +                                           GFP_KERNEL_ACCOUNT);
>         if (!ubuf->pinned_folios)
>                 return -ENOMEM;
> 
> @@ -387,7 +388,7 @@ static long udmabuf_create(struct miscdevice *device,
>         if (ret)
>                 goto err;
> 
> -       folios = kvmalloc_objs(*folios, max_nr_folios);
> +       folios = kvmalloc_objs(*folios, max_nr_folios, GFP_KERNEL_ACCOUNT);
>         if (!folios) {
>                 ret = -ENOMEM;
>                 goto err;
> --
> 2.43.0
>