Re: [PATCH v4 5/6] drm/gem-shmem: Track folio accessed/dirty status in mmap

[Tommaso Merciai]

Hi Thomas,

On 3/13/26 09:33, Thomas Zimmermann wrote:

Hi

Am 12.03.26 um 18:46 schrieb Biju Das:

Hi Tommaso,

-----Original Message-----
From: Tommaso Merciai <tommaso.merciai...@bp.renesas.com>
Sent: 12 March 2026 17:37

Subject: Re: [PATCH v4 5/6] drm/gem-shmem: Track folio accessed/dirty status in mmap

Hi Thomas,
Thanks for your patch.

I'm working on DSI support for RZ/G3E from this morning rebasing on top of next-20260311 I'm seeing

that weston hang on my side:

Reverting this patch fix the issue.
(git revert 28e3918179aa)

Just a guess, but maybe vm_file is NULL. The attached patch should handle this. Could either of you please test?

Same here, no luck.
Thanks for sharing.

Kind Regards,
Tommaso

Best regards
Thomas

I'm wondering if anyone encountered this issue?
Thanks in advance.

I am also seeing same issue on RZ/G3L with weston.

Cheers,
Biju

Kind Regards,
Tommaso

On Fri, Feb 27, 2026 at 12:42:10PM +0100, Thomas Zimmermann wrote:

Invoke folio_mark_accessed() in mmap page faults to add the folio to
the memory manager's LRU list. Userspace invokes mmap to get the
memory for software rendering. Compositors do the same when creating
the final on-screen image, so keeping the pages in LRU makes sense.
Avoids paging out graphics buffers when under memory pressure.

In pfn_mkwrite, further invoke the folio_mark_dirty() to add the folio

for writeback should the underlying file be paged out from system memory. This rarely happens in practice, yet it would corrupt the buffer content.

This has little effect on a system's hardware-accelerated rendering,

which only mmaps for an initial setup of textures, meshes, shaders, etc.

v4:
- test for VM_FAULT_NOPAGE before marking folio as accessed (Boris)
- test page-array bounds in mkwrite handler (Boris)
v3:
- rewrite for VM_PFNMAP
v2:
- adapt to changes in drm_gem_shmem_try_mmap_pmd()

Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
Reviewed-by: Boris Brezillon <boris.brezil...@collabora.com>
---
  drivers/gpu/drm/drm_gem_shmem_helper.c | 22 ++++++++++++++++++++++
  1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index cefa50eaf7a4..1ab2bbd3860c 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -598,6 +598,9 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)

      if (ret != VM_FAULT_NOPAGE)
          ret = vmf_insert_pfn(vma, vmf->address, pfn);

+    if (ret == VM_FAULT_NOPAGE)
+        folio_mark_accessed(folio);
+
  out:
      dma_resv_unlock(obj->resv);

@@ -638,10 +641,29 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)

      drm_gem_vm_close(vma);
  }

+static vm_fault_t drm_gem_shmem_pfn_mkwrite(struct vm_fault *vmf) {
+    struct vm_area_struct *vma = vmf->vma;
+    struct drm_gem_object *obj = vma->vm_private_data;
+    struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+    loff_t num_pages = obj->size >> PAGE_SHIFT;
+    pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset
+within VMA */
+

+    if (drm_WARN_ON(obj->dev, !shmem->pages || page_offset >= num_pages))

+        return VM_FAULT_SIGBUS;
+
+    file_update_time(vma->vm_file);
+
+    folio_mark_dirty(page_folio(shmem->pages[page_offset]));
+
+    return 0;
+}
+
  const struct vm_operations_struct drm_gem_shmem_vm_ops = {
      .fault = drm_gem_shmem_fault,
      .open = drm_gem_shmem_vm_open,
      .close = drm_gem_shmem_vm_close,
+    .pfn_mkwrite = drm_gem_shmem_pfn_mkwrite,
  };
  EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);

--
2.52.0