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

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Message-ID: <CABdmKX2MPhw121ZG8V+f-XoOReUsCdmcug-cWDg=3WZcJ=NHHA@mail.gmail.com>
Date: Fri, 12 Dec 2025 08:25:19 +0900
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Eric Chanudet <echanude@...hat.com>
Cc: Sumit Semwal <sumit.semwal@...aro.org>, 
	Benjamin Gaignard <benjamin.gaignard@...labora.com>, Brian Starkey <Brian.Starkey@....com>, 
	John Stultz <jstultz@...gle.com>, Christian Koenig <christian.koenig@....com>, 
	Maxime Ripard <mripard@...hat.com>, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
	linux-kernel@...r.kernel.org, 
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>
Subject: Re: [PATCH] dma-buf: system_heap: account for system heap allocation
 in memcg

On Fri, Dec 12, 2025 at 4:31 AM Eric Chanudet <echanude@...hat.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@...hat.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
>