Re: [PATCH] drm/ttm: fix ttm tt init fail when size exceeds kmalloc limit

[AMD Official Use Only]

________________________________ From: Koenig, Christian Christian.Koenig@amd.com Sent: Wednesday, April 20, 2022 5:00 PM To: Wang, Yang(Kevin) KevinYang.Wang@amd.com; dri-devel@lists.freedesktop.org dri-devel@lists.freedesktop.org; amd-gfx@lists.freedesktop.org amd-gfx@lists.freedesktop.org Subject: Re: [PATCH] drm/ttm: fix ttm tt init fail when size exceeds kmalloc limit

Am 20.04.22 um 10:56 schrieb Yang Wang:

if the __GFP_ZERO is set, the kvmalloc() can't fallback to use vmalloc()

Hui what? Why should kvmalloc() not be able to fallback to vmalloc() when __GFP_ZERO is set?

And even that is really the case then that sounds like a bug in kvmalloc().

Regards, Christian.

[kevin]: it is really test case from libdrm amdgpu test, which try to allocate a big BO which will cause ttm tt init fail. it may be a kvmalloc() bug, and this patch can as a workaround in ttm before this issue fix.

void *kvmalloc_node(size_t size, gfp_t flags, int node) { ... if ((flags & GFP_KERNEL) != GFP_KERNEL) return kmalloc_node(size, flags, node); ... }

Best Regards, Kevin

to allocate memory, when request size is exceeds kmalloc limit, it will cause allocate memory fail.

e.g: when ttm want to create a BO with 1TB size, it maybe fail.

Signed-off-by: Yang Wang KevinYang.Wang@amd.com

drivers/gpu/drm/ttm/ttm_tt.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c index 79c870a3bef8..9f2f3e576b8d 100644 --- a/drivers/gpu/drm/ttm/ttm_tt.c +++ b/drivers/gpu/drm/ttm/ttm_tt.c @@ -97,9 +97,12 @@ int ttm_tt_create(struct ttm_buffer_object *bo, bool zero_alloc) static int ttm_tt_alloc_page_directory(struct ttm_tt *ttm) { ttm->pages = kvmalloc_array(ttm->num_pages, sizeof(void*),

•                 GFP_KERNEL | __GFP_ZERO);
  

•                             GFP_KERNEL);
   if (!ttm->pages)
           return -ENOMEM;
  

• memset(ttm->pages, 0, ttm->num_pages * sizeof(void *));
  

•  return 0;
  

  }

@@ -108,10 +111,12 @@ static int ttm_dma_tt_alloc_page_directory(struct ttm_tt *ttm) ttm->pages = kvmalloc_array(ttm->num_pages, sizeof(*ttm->pages) + sizeof(*ttm->dma_address),

•                             GFP_KERNEL | __GFP_ZERO);
  

•                             GFP_KERNEL);
   if (!ttm->pages)
           return -ENOMEM;
  
  

• memset(ttm->pages, 0, ttm->num_pages * (sizeof(*ttm->pages) + sizeof(*ttm->dma_address)));
  

•  ttm->dma_address = (void *)(ttm->pages + ttm->num_pages);
   return 0;
  

  }

@@ -120,9 +125,12 @@ static int ttm_sg_tt_alloc_page_directory(struct ttm_tt *ttm) { ttm->dma_address = kvmalloc_array(ttm->num_pages, sizeof(*ttm->dma_address),

•                                   GFP_KERNEL | __GFP_ZERO);
  

•                                   GFP_KERNEL);
   if (!ttm->dma_address)
           return -ENOMEM;
  

• memset(ttm->dma_address, 0, ttm->num_pages * sizeof(*ttm->dma_address));
  

•  return 0;
  

  }