linux-kernel - Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

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Date:   Fri, 24 Jul 2020 11:36:55 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Amit Pundir <amit.pundir@...aro.org>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        David Rientjes <rientjes@...gle.com>,
        linux-rpi-kernel@...ts.infradead.org, jeremy.linton@....com,
        iommu@...ts.linux-foundation.org,
        lkml <linux-kernel@...r.kernel.org>,
        John Stultz <john.stultz@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

Hi Amit,

On Thu, 2020-07-23 at 10:44 +0530, Amit Pundir wrote:
> Hi Nicolas,
> 
> Sorry I got stuck on other things yesterday.

No worries :)

> On Tue, 21 Jul 2020 at 21:57, Nicolas Saenz Julienne

[...]

> > 
> > Let's get a bigger hammer, I'm just looking for clues here. Can you
> > apply this and provide the dmesg output.
> > 
> > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> > index 6bc74a2d5127..2160676bf488 100644
> > --- a/kernel/dma/pool.c
> > +++ b/kernel/dma/pool.c
> > @@ -268,6 +268,8 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
> >                         schedule_work(&atomic_pool_work);
> >         }
> > 
> > +       dev_info(dev, "%s: size %lx, phys addr %llx, flags 0x%x\n", __func__, size, phys, flags);
> > +
> >         return ptr;
> >  }
> 
> I never made it to dma_alloc_from_pool() call from
> dma_direct_alloc_pages(), dma_should_alloc_from_pool() returns False
> from gfpflags_allow_blocking() block.

I'm a little sceptical about this. The only way you can get memory from these
pools is through dma_alloc_from_pool(), and given how changes in the pool
initialization affected the phone, it's pretty clear some amount of pool
allocation is happening.

Regards,
Nicolas