On Fri, 5 Jan 2024 21:46:18 +0300 Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote: > SGT isn't refcounted. Once SGT pointer has been obtained, it remains the > same for both locked and unlocked get_pages_sgt(). Return cached SGT > directly without taking a potentially expensive lock. > > Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> but I'm wondering if we should have made this change directly in 'drm/shmem-helper: Change sgt allocation policy'. > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 8fd7851c088b..e6e6e693ab95 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -962,6 +962,18 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem) > drm_WARN_ON(obj->dev, drm_gem_shmem_is_purgeable(shmem))) > return ERR_PTR(-EBUSY); > > + /* > + * Drivers that use shrinker should take into account that shrinker > + * may relocate BO, thus invalidating the returned SGT pointer. > + * Such drivers should pin GEM while they use SGT. > + * > + * Drivers that don't use shrinker should take into account that > + * SGT is released together with the GEM pages. Pages should be kept > + * alive while SGT is used. > + */ > + if (shmem->sgt) > + return shmem->sgt; > + > ret = dma_resv_lock_interruptible(shmem->base.resv, NULL); > if (ret) > return ERR_PTR(ret);
