Re: [PATCH] dma-buf: system_heap: account for system heap allocation in memcg

["T.J. Mercier" <tjmercier@google.com>]

On Fri, Dec 12, 2025 at 4:31 AM Eric Chanudet <echanude@redhat.com> wrote:
>
> The system dma-buf heap lets userspace allocate buffers from the page
> allocator. However, these allocations are not accounted for in memcg,
> allowing processes to escape limits that may be configured.
>
> Pass the __GFP_ACCOUNT for our allocations to account them into memcg.

We had a discussion just last night in the MM track at LPC about how
shared memory accounted in memcg is pretty broken. Without a way to
identify (and possibly transfer) ownership of a shared buffer, this
makes the accounting of shared memory, and zombie memcg problems
worse. :\

>
> Userspace components using the system heap can be constrained with, e.g:
>   systemd-run --user --scope -p MemoryMax=10M ...
>
> Signed-off-by: Eric Chanudet <echanude@redhat.com>
> ---
>  drivers/dma-buf/heaps/system_heap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 4c782fe33fd4..c91fcdff4b77 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -38,10 +38,10 @@ struct dma_heap_attachment {
>         bool mapped;
>  };
>
> -#define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO)
> +#define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO | __GFP_ACCOUNT)
>  #define HIGH_ORDER_GFP  (((GFP_HIGHUSER | __GFP_ZERO | __GFP_NOWARN \
>                                 | __GFP_NORETRY) & ~__GFP_RECLAIM) \
> -                               | __GFP_COMP)
> +                               | __GFP_COMP | __GFP_ACCOUNT)
>  static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP};
>  /*
>   * The selection of the orders used for allocation (1MB, 64K, 4K) is designed
> --
> 2.52.0
>