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

[Felix Kuehling <felix.kuehling@xxxxxxx>]

On 2025-01-06 21:10, Deng, Emily wrote:
> [AMD Official Use Only - AMD Internal Distribution Only]
>
> > -----Original Message-----
> > From: Kuehling, Felix <Felix.Kuehling@xxxxxxx>
> > Sent: Tuesday, January 7, 2025 4:53 AM
> > To: Deng, Emily <Emily.Deng@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> > Subject: Re: [PATCH] drm/amdkfd: Fix partial migrate issue
> >
> >
> > On 2025-01-05 20:45, Deng, Emily wrote:
> > > [AMD Official Use Only - AMD Internal Distribution Only]
> > >
> > > > -----Original Message-----
> > > > From: Kuehling, Felix <Felix.Kuehling@xxxxxxx>
> > > > Sent: Saturday, January 4, 2025 7:10 AM
> > > > To: Deng, Emily <Emily.Deng@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> > > > Subject: Re: [PATCH] drm/amdkfd: Fix partial migrate issue
> > > >
> > > >
> > > > On 2025-01-02 19:06, 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>
> > > > Good catch. But I think it's still not quite right. See inline.
> > > >
> > > >
> > > > > ---
> > > > >     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;
> > > > >        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)) {
> > > > We should also check (migrate->src[i] & MIGRATE_PFN_MIGRATE) to catch
> > > > only the pages that are ready to migrate (i.e. not already in device
> > > > memory and not pinned by someone else).
> > > >
> > > > Regards,
> > > >     Felix
> > > > The code " if (spage && !is_zone_device_page(spage)) {" is already checked
> > whether the page could be migrated or not. Because after called migrate_vma_setup,
> > for those pages couldn't be migrated it will be set to NULL.
> >
> > The page may be non-NULL. If the MIGRATE_PFN_MIGRATE is not set, the page
> > could not be collected for migration by migrate_vma_setup and it should not be
> > migrated. See
> > https://elixir.bootlin.com/linux/v6.12.6/source/mm/migrate_device.c#L470
> >
> > Regards,
> >    Felix
> Sorry, don't understand clearly. If a page couldn't be migrated, the src should be set NULL, if not, I think it is the migrate_vma_collect's bug. So could you point which code path
> it will not be NULL.

Looks like I misread the documentation. I thought there could be cases 
where a valid page would have the MIGRATE_PFN_MIGRATE flag unset. But I 
can't find that in the code in mm/migrate_device.c. In the cases where a 
page cannot be collected, the src entry will be 0. The only case I see 
where the MIGRATE_PFN_MIGRATE flag is significant is in cases where host 
memory was not allocated yet (PFN is 0) but the migration can allocate 
0-initialized device memory for it.

Regards,
  Felix


> > > Emily Deng
> > > Best Wishes
> > >
> > >
> > > > > @@ -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]);
> > > > >        }
> > > > >
> > > > >        r = svm_migrate_copy_memory_gart(adev, src + i - j, dst + i -
> > > > > j, j,