On 2019-02-18 3:39 p.m., Thomas Hellstrom wrote:
On Mon, 2019-02-18 at 18:07 +0100, Christian König wrote:
Am 18.02.19 um 10:47 schrieb Thomas Hellstrom:
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.
Yeah, I'm perfectly aware of this. But this is for the accounting size!
We have an accounting for the stuff needed additional to the pages backing the BO (e.g. the page and DMA addr array).
And from the bug description it sounds like we use the DMA32 zone for this accounting which of course is completely nonsense.
It's actually accounted in all available zones, since it would be pretty hard to determine exactly where that memory should be accounted. In particular if it's vmalloced. It might be DMA32, it might not. Given the objective of stopping malicious user-space from exhausting the DMA32 zone it was, at the time the code was written, a reasonable approximation. With ever increasing memory sizes, there might be better solutions?
As far as I can see, in TTM, ttm_mem_global_alloc is only used for the acc_size in ttm_bo_init_reserved. Other than that vmwgfx also seems to use it to account for a few things that are allocated with kmalloc.
So would a better solution be to change ttm_mem_global_alloc to use only the kernel zone?
Regards, Felix
/Thomas
Christian.
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@amd.com CC: thellstrom@vmware.com CC: christian.koenig@amd.com
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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