linux-kernel - [PATCH v17 06/18] drm/shmem-helper: Add and use pages_pin

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Date:   Fri, 15 Sep 2023 02:27:09 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     David Airlie <airlied@...il.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Christian König <christian.koenig@....com>,
        Qiang Yu <yuq825@...il.com>,
        Steven Price <steven.price@....com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Emma Anholt <emma@...olt.net>, Melissa Wen <mwen@...lia.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: [PATCH v17 06/18] drm/shmem-helper: Add and use pages_pin_count

Add separate pages_pin_count for tracking of whether drm-shmem pages are
moveable or not. With the addition of memory shrinker support to drm-shmem,
the pages_use_count will no longer determine whether pages are hard-pinned
in memory, but whether pages exist and are soft-pinned (and could be swapped
out). The pages_pin_count > 1 will hard-pin pages in memory.

Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 24 ++++++++++++++++--------
 include/drm/drm_gem_shmem_helper.h     | 10 ++++++++++
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 2cc0601865f6..286f0ca51309 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -234,18 +234,16 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 
 	dma_resv_assert_held(shmem->base.resv);
 
+	if (refcount_inc_not_zero(&shmem->pages_pin_count))
+		return 0;
+
 	ret = drm_gem_shmem_get_pages_locked(shmem);
+	if (!ret)
+		refcount_set(&shmem->pages_pin_count, 1);
 
 	return ret;
 }
 
-static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
-{
-	dma_resv_assert_held(shmem->base.resv);
-
-	drm_gem_shmem_put_pages_locked(shmem);
-}
-
 /**
  * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
  * @shmem: shmem GEM object
@@ -263,6 +261,9 @@ int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
+	if (refcount_inc_not_zero(&shmem->pages_pin_count))
+		return 0;
+
 	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
 	if (ret)
 		return ret;
@@ -286,8 +287,14 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
+	if (refcount_dec_not_one(&shmem->pages_pin_count))
+		return;
+
 	dma_resv_lock(shmem->base.resv, NULL);
-	drm_gem_shmem_unpin_locked(shmem);
+
+	if (refcount_dec_and_test(&shmem->pages_pin_count))
+		drm_gem_shmem_put_pages_locked(shmem);
+
 	dma_resv_unlock(shmem->base.resv);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin);
@@ -632,6 +639,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
 	if (shmem->base.import_attach)
 		return;
 
+	drm_printf_indent(p, indent, "pages_pin_count=%u\n", refcount_read(&shmem->pages_pin_count));
 	drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
 	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
 	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 6ee4a4046980..268b3127d150 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -39,6 +39,16 @@ struct drm_gem_shmem_object {
 	 */
 	unsigned int pages_use_count;
 
+	/**
+	 * @pages_pin_count:
+	 *
+	 * Reference count on the pinned pages table.
+	 * The pages allowed to be evicted and purged by memory
+	 * shrinker only when the count is zero, otherwise pages
+	 * are hard-pinned in memory.
+	 */
+	refcount_t pages_pin_count;
+
 	/**
 	 * @madv: State for madvise
 	 *
-- 
2.41.0