On Mon, 2019-02-18 at 09:20 +0000, Koenig, Christian wrote:
> Another good question is also why the heck the acc_size counts
> towards
> the DMA32 zone?
DMA32 TTM pages are accounted in the DMA32 zone. Other pages are not.
For small persistent allocations using ttm_mem_global_alloc(), they are
accounted also in the DMA32 zone, which may cause over-accounting of
that zone, but that's pretty unlikely to be a big problem..
/Thomas
>
> In other words why should the internal bookkeeping pages be allocated
> in
> the DMA32 zone?
>
> That doesn't sounds valid to me in any way,
> Christian.
>
> Am 18.02.19 um 09:02 schrieb Thomas Hellstrom:
> > Hmm,
> >
> > This zone was intended to stop TTM page allocations from
> > exhausting
> > the DMA32 zone. IIRC dma_alloc_coherent() uses DMA32 by default,
> > which
> > means if we drop this check, other devices may stop functioning
> > unexpectedly?
> >
> > However, in the end I'd expect the kernel page allocation system
> > to
> > make sure there are some pages left in the DMA32 zone, otherwise
> > random non-IO page allocations would also potentially exhaust the
> > DMA32 zone without anybody caring, which means removing this zone
> > wouldn't be any worse than whatever other subsystems may be doing
> > already...
> >
> > /Thomas
> >
> >
> > On 2/16/19 12:02 AM, Kuehling, Felix wrote:
> > > This is an RFC. I'm not sure this is the right solution, but it
> > > highlights the problem I'm trying to solve.
> > >
> > > The dma32_zone limits the acc_size of all allocated BOs to 2GB.
> > > On a
> > > 64-bit system with hundreds of GB of system memory and GPU
> > > memory,
> > > this can become a bottle neck. We're seeing TTM memory allocation
> > > failures not because we're truly out of memory, but because we're
> > > out of space in the dma32_zone for the acc_size needed for our BO
> > > book-keeping.
> > >
> > > Signed-off-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
> > > CC: thellstrom@xxxxxxxxxx
> > > CC: christian.koenig@xxxxxxx
> > > ---
> > > drivers/gpu/drm/ttm/ttm_memory.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/ttm/ttm_memory.c
> > > b/drivers/gpu/drm/ttm/ttm_memory.c
> > > index f1567c3..bb05365 100644
> > > --- a/drivers/gpu/drm/ttm/ttm_memory.c
> > > +++ b/drivers/gpu/drm/ttm/ttm_memory.c
> > > @@ -363,7 +363,7 @@ static int ttm_mem_init_highmem_zone(struct
> > > ttm_mem_global *glob,
> > > glob->zones[glob->num_zones++] = zone;
> > > return 0;
> > > }
> > > -#else
> > > +#elifndef CONFIG_64BIT
> > > static int ttm_mem_init_dma32_zone(struct ttm_mem_global *glob,
> > > const struct sysinfo *si)
> > > {
> > > @@ -441,7 +441,7 @@ int ttm_mem_global_init(struct ttm_mem_global
> > > *glob)
> > > ret = ttm_mem_init_highmem_zone(glob, &si);
> > > if (unlikely(ret != 0))
> > > goto out_no_zone;
> > > -#else
> > > +#elifndef CONFIG_64BIT
> > > ret = ttm_mem_init_dma32_zone(glob, &si);
> > > if (unlikely(ret != 0))
> > > goto out_no_zone;
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