[PATCH 2/3] drm/gem-shmem: Track folio accessed/dirty status in mmap

[Thomas Zimmermann <tzimmermann@suse.de>]

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. Later compositors will do the same to create the
final on-screen image, so keeping the pages in LRU makes sense. Avoids
paging out graphics buffers when under memory pressure.

In page_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.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index b6ddabbfcc52..30cd34d3a111 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -562,8 +562,10 @@ static bool drm_gem_shmem_try_map_pmd(struct vm_fault *vmf, unsigned long addr,
 
 		if (folio_test_pmd_mappable(folio)) {
 			/* Read-only mapping; split upon write fault */
-			if (vmf_insert_folio_pmd(vmf, folio, false) == VM_FAULT_NOPAGE)
+			if (vmf_insert_folio_pmd(vmf, folio, false) == VM_FAULT_NOPAGE) {
+				folio_mark_accessed(folio);
 				return true;
+			}
 		}
 	}
 #endif
@@ -605,6 +607,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
 		get_page(page);
 
 		folio_lock(folio);
+		folio_mark_accessed(folio);
 
 		vmf->page = page;
 		ret = VM_FAULT_LOCKED;
@@ -653,10 +656,23 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)
 	drm_gem_vm_close(vma);
 }
 
+static vm_fault_t drm_gem_shmem_page_mkwrite(struct vm_fault *vmf)
+{
+	struct folio *folio = page_folio(vmf->page);
+
+	file_update_time(vmf->vma->vm_file);
+
+	folio_lock(folio);
+	folio_mark_dirty(folio);
+
+	return VM_FAULT_LOCKED;
+}
+
 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,
+	.page_mkwrite = drm_gem_shmem_page_mkwrite,
 };
 EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
 
-- 
2.52.0