Re: [PATCH] drm/amdkfd: Fix partial migrate issue

["Chen, Xiaogang" <xiaogang.chen@xxxxxxx>]

On 1/6/2025 8:02 PM, Deng, Emily wrote:

[AMD Official Use Only - AMD Internal Distribution Only]

 

 

From: Chen, Xiaogang <Xiaogang.Chen@xxxxxxx>
Sent: Monday, January 6, 2025 11:27 PM
To: Deng, Emily <Emily.Deng@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH] drm/amdkfd: Fix partial migrate issue

 

 

On 1/2/2025 6:06 PM, Emily Deng wrote:

For partial migrate from ram to vram, the migrate->cpages is not

equal to migrate->npages, should use migrate->npages to check all needed

migrate pages which could be copied or not.

And only need to set those pages could be migrated to migrate->dst[i], or

the migrate_vma_pages will migrate the wrong pages based on the migrate->dst[i].

Signed-off-by: Emily Deng <Emily.Deng@xxxxxxx>

---

 drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 8 ++++----

 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c

index 4b275937d05e..5c96c2d425e3 100644

--- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c

+++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c

@@ -278,7 +278,7 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct svm_range *prange,

                         struct migrate_vma *migrate, struct dma_fence **mfence,

                         dma_addr_t *scratch, uint64_t ttm_res_offset)

 {

-       uint64_t npages = migrate->cpages;

+       uint64_t npages = migrate->npages;

I agree this part.

        struct amdgpu_device *adev = node->adev;

        struct device *dev = adev->dev;

        struct amdgpu_res_cursor cursor;

@@ -299,9 +299,6 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct svm_range *prange,

                struct page *spage;

                dst[i] = cursor.start + (j << PAGE_SHIFT);

-               migrate->dst[i] = svm_migrate_addr_to_pfn(adev, dst[i]);

-        svm_migrate_get_vram_page(prange, migrate->dst[i]);

-               migrate->dst[i] = migrate_pfn(migrate->dst[i]);

                spage = migrate_pfn_to_page(migrate->src[i]);

                if (spage && !is_zone_device_page(spage)) {

@@ -345,6 +342,9 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct svm_range *prange,

                } else {

                        j++;

                }

+               migrate->dst[i] = svm_migrate_addr_to_pfn(adev, dst[i]);

+        svm_migrate_get_vram_page(prange, migrate->dst[i]);

+               migrate->dst[i] = migrate_pfn(migrate->dst[i]);

I think what current code misses here is that migrate->dst[i] should match migrate->src[i]: migrate->dst[i](vram page) got set for page that will be migrated from system ram, otherwise migrate->dst[i] should be zero. Your change makes migrates->dst[i] not set though its page has been migrated by svm_migrate_copy_memory_gart for the case that cpages != npages, because you set migrate->dst[i] at end of loop and use 'continue' after migration.

The page migration happens at svm_migrate_copy_memory_gart, not migrate_vma_pages that migrates struct page meta-data from source struct page to destination struct page and has mmu notification.

Regards

Xiaogang

The migrate->dst[i] default value is 0. The purpose of the change is to match the migrate->dst[i] and migrate->src[i]. And for svm_migrate_copy_to_vram, it only will call svm_migrate_copy_memory_gart to copy those pages which need to be migrated, for those don’t need migrate pages, it won’t call svm_migrate_copy_memory_gart.

Yes, the issue here is we need match migrate->dst[i] and migrate->src[i]: migrate->dst[i] need be set only when its correspondent migrate->src[i] page will be migrated or the src page has dma address setup by dma_map_page. Then why not set migrate->dst[i] at same time when have dma_map_page for src page? That way will simplify the logic and not need use amdgpu_res_next to jump vram cursor.

Regards

Xiaogang

        }

        r = svm_migrate_copy_memory_gart(adev, src + i - j, dst + i - j, j,