Re: [PATCH] drm/amdkfd: Change page discontinuity handling at svm_migrate_copy_to_vram

[Chen, Xiaogang]

On 1/20/2025 10:13 AM, Philip Yang wrote:


On 2025-01-15 16:40, Xiaogang.Chen wrote:
From: Xiaogang Chen<xiaogang.c...@amd.com>

Current svm_migrate_copy_to_vram handles sys pages(src) and dst pages (vram)
discontinuation in different way. When src got discontinuity migrates j pages
that ith page is not migrated; When dst got discontinuity migrates j+1 pages
that ith page is migrated. That cause error path have to iterate all pages to
find which page got migrated before error happened. Also makes code more
difficult to read.
error handling path loop from 0 -> mpages or i -> 0, to rollback 
migrated pages, I think both way should handle similar number of pages.
same number to call svm_migrate_put_vram_page, the loop number is not 
same. The change is not about correctness, but make the code more 
straight forward to read. At error path a more logical way is rollback 
from the place where the error happened, instead browse all pages.
This patch handles src and dst page discontinuity in consistent way, has its
logic and error recovery straight forward.

I feel that svm_migrate_copy_memory_gart move to the beginning of the 
loop is harder to understand.

If you feel handle vram page discontinuation at beginning of loop is not 
natural we can put it after sys ram discontinuation handling. The 
purpose is handling src/dst page discontinuity in consistent way.


Regards,

Philip

Signed-off-by: Xiaogang Chen<xiaogang.c...@amd.com>
---
  drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 68 ++++++++++++------------
  1 file changed, 35 insertions(+), 33 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c 
b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
index d05d199b5e44..2ce78c77f203 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
@@ -299,6 +299,19 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct 
svm_range *prange,
        for (i = j = 0; (i < npages) && (mpages < migrate->cpages); i++) {
                struct page *spage;
  
+		/* accumulated pages more than current cursor's block has */
+               if (j >= (cursor.size >> PAGE_SHIFT)) {
+                       r = svm_migrate_copy_memory_gart(adev, src + i - j,
+                                                        dst + i - j, j,
+                                                        FROM_RAM_TO_VRAM,
+                                                        mfence);
+                       if (r)
+                               goto out_free_vram_pages;
+
+                       amdgpu_res_next(&cursor, j * PAGE_SIZE);
+                       j = 0;
+               }
+
                if (migrate->src[i] & MIGRATE_PFN_MIGRATE) {
                        dst[i] = cursor.start + (j << PAGE_SHIFT);
                        migrate->dst[i] = svm_migrate_addr_to_pfn(adev, dst[i]);
@@ -306,17 +319,10 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct 
svm_range *prange,
                        migrate->dst[i] = migrate_pfn(migrate->dst[i]);
                        mpages++;
                }
+
                spage = migrate_pfn_to_page(migrate->src[i]);
-               if (spage && !is_zone_device_page(spage)) {
-                       src[i] = dma_map_page(dev, spage, 0, PAGE_SIZE,
-                                             DMA_BIDIRECTIONAL);
-                       r = dma_mapping_error(dev, src[i]);
-                       if (r) {
-                               dev_err(dev, "%s: fail %d dma_map_page\n",
-                                       __func__, r);
-                               goto out_free_vram_pages;
-                       }
-               } else {
+               if (!spage || is_zone_device_page(spage)) {
+                       /* sdma accumulated pages before src got gap */
                        if (j) {
                                r = svm_migrate_copy_memory_gart(
                                                adev, src + i - j,
@@ -325,29 +331,26 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct 
svm_range *prange,
                                                mfence);
                                if (r)
                                        goto out_free_vram_pages;
-                               amdgpu_res_next(&cursor, (j + 1) << PAGE_SHIFT);
+
+                               amdgpu_res_next(&cursor, (j+1) << PAGE_SHIFT);
                                j = 0;
-                       } else {
+                       } else
                                amdgpu_res_next(&cursor, PAGE_SIZE);
-                       }
+
                        continue;
                }
  
-		pr_debug_ratelimited("dma mapping src to 0x%llx, pfn 0x%lx\n",
-                                    src[i] >> PAGE_SHIFT, page_to_pfn(spage));
-
-               if (j >= (cursor.size >> PAGE_SHIFT) - 1 && i < npages - 1) {
-                       r = svm_migrate_copy_memory_gart(adev, src + i - j,
-                                                        dst + i - j, j + 1,
-                                                        FROM_RAM_TO_VRAM,
-                                                        mfence);
-                       if (r)
-                               goto out_free_vram_pages;
-                       amdgpu_res_next(&cursor, (j + 1) * PAGE_SIZE);
-                       j = 0;
-               } else {
-                       j++;
+               src[i] = dma_map_page(dev, spage, 0, PAGE_SIZE,
+                               DMA_BIDIRECTIONAL);
+               r = dma_mapping_error(dev, src[i]);
+               if (r) {
+                       dev_err(dev, "%s: fail %d dma_map_page\n", __func__, r);
+                       goto out_free_vram_pages;
                }
+
+               pr_debug_ratelimited("dma mapping src to 0x%llx, pfn 0x%lx\n",
+                                                        src[i] >> PAGE_SHIFT, 
page_to_pfn(spage));
+               j++;
        }
  
  	r = svm_migrate_copy_memory_gart(adev, src + i - j, dst + i - j, j,
@@ -356,12 +359,11 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct 
svm_range *prange,
  out_free_vram_pages:
        if (r) {
                pr_debug("failed %d to copy memory to vram\n", r);
-               for (i = 0; i < npages && mpages; i++) {
-                       if (!dst[i])
-                               continue;
-                       svm_migrate_put_vram_page(adev, dst[i]);
-                       migrate->dst[i] = 0;
-                       mpages--;
+               while (i--) {
+                       if (migrate->dst[i]) {
+                               svm_migrate_put_vram_page(adev, dst[i]);
+                               migrate->dst[i] = 0;
+                       }
                }
        }