Re: [PATCH v2 2/2] dma-buf: system_heap: account for system heap allocation in memcg

[Eric Chanudet]

On Wed, Jan 14, 2026 at 11:38:27AM +0100, Christian König wrote:
> On 1/13/26 22:32, Eric Chanudet 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 __GFP_ACCOUNT for system heap allocations, based on the
> > dma_heap.mem_accounting parameter, to use memcg and account for them.
> > 
> > Signed-off-by: Eric Chanudet <echanude@xxxxxxxxxx>
> > ---
> >  drivers/dma-buf/heaps/system_heap.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> > index 4c782fe33fd497a74eb5065797259576f9b651b6..139b50df64ed4c4a6fdd69f25fe48324fbe2c481 100644
> > --- a/drivers/dma-buf/heaps/system_heap.c
> > +++ b/drivers/dma-buf/heaps/system_heap.c
> > @@ -52,6 +52,8 @@ static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP};
> >  static const unsigned int orders[] = {8, 4, 0};
> >  #define NUM_ORDERS ARRAY_SIZE(orders)
> >  
> > +extern bool mem_accounting;
> 
> Please define that in some header. Apart from that looks good technically.

Thank you for the review, I can move it to linux/dma-heap.h in a v3
since it's intended for other heaps as well.

> But after the discussion it sounds more and more like we don't want to account device driver allocated memory in memcg at all.

>From the threads in v1 I thought adding the switch left open a
consideration to use memcg with driver allocated memory for userspace,
even with the known caveats that implies. Re-reading your last reply[1],
that's not quite the case it sounds like.

Best,

[1] https://lore.kernel.org/all/e38d87d3-a114-43f9-be93-03e9b9f40844@xxxxxxx/

> 
> Regards,
> Christian.
> 
> 
> > +
> >  static int dup_sg_table(struct sg_table *from, struct sg_table *to)
> >  {
> >  	struct scatterlist *sg, *new_sg;
> > @@ -320,14 +322,17 @@ static struct page *alloc_largest_available(unsigned long size,
> >  {
> >  	struct page *page;
> >  	int i;
> > +	gfp_t flags;
> >  
> >  	for (i = 0; i < NUM_ORDERS; i++) {
> >  		if (size <  (PAGE_SIZE << orders[i]))
> >  			continue;
> >  		if (max_order < orders[i])
> >  			continue;
> > -
> > -		page = alloc_pages(order_flags[i], orders[i]);
> > +		flags = order_flags[i];
> > +		if (mem_accounting)
> > +			flags |= __GFP_ACCOUNT;
> > +		page = alloc_pages(flags, orders[i]);
> >  		if (!page)
> >  			continue;
> >  		return page;
> > 
> 

-- 
Eric Chanudet