| Message ID | 20230827175449.1766701-3-dmitry.osipenko@collabora.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add generic memory shrinker to VirtIO-GPU and Panfrost DRM drivers | expand |
On Sun, 27 Aug 2023 20:54:28 +0300 Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote: > Use separate flag for tracking page count bumped by shmem->sgt to avoid > imbalanced page counter during of drm_gem_shmem_free() time. It's fragile > to assume that populated shmem->pages at a freeing time means that the > count was bumped by drm_gem_shmem_get_pages_sgt(), using a flag removes > the ambiguity. > > Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ++- > drivers/gpu/drm/lima/lima_gem.c | 1 + > include/drm/drm_gem_shmem_helper.h | 7 +++++++ > 3 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 78d9cf2355a5..db20b9123891 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -152,7 +152,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > sg_free_table(shmem->sgt); > kfree(shmem->sgt); > } > - if (shmem->pages) > + if (shmem->got_sgt) > drm_gem_shmem_put_pages(shmem); Can't we just move this drm_gem_shmem_put_pages() call in the if (shmem->sgt) block? > > drm_WARN_ON(obj->dev, shmem->pages_use_count); > @@ -687,6 +687,7 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_ > if (ret) > goto err_free_sgt; > > + shmem->got_sgt = true; > shmem->sgt = sgt; > > return sgt; > diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c > index 4f9736e5f929..28602302c281 100644 > --- a/drivers/gpu/drm/lima/lima_gem.c > +++ b/drivers/gpu/drm/lima/lima_gem.c > @@ -89,6 +89,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm) > } > > *bo->base.sgt = sgt; > + bo->base.got_sgt = true; > > if (vm) { > ret = lima_vm_map_bo(vm, bo, old_size >> PAGE_SHIFT); > diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h > index ec70a98a8fe1..f87124629bb5 100644 > --- a/include/drm/drm_gem_shmem_helper.h > +++ b/include/drm/drm_gem_shmem_helper.h > @@ -73,6 +73,13 @@ struct drm_gem_shmem_object { > */ > unsigned int vmap_use_count; > > + /** > + * @got_sgt: > + * > + * True if SG table was retrieved using drm_gem_shmem_get_pages_sgt() > + */ > + bool got_sgt : 1; > + > /** > * @imported_sgt: > *
On 8/28/23 13:55, Boris Brezillon wrote: > On Sun, 27 Aug 2023 20:54:28 +0300 > Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote: > >> Use separate flag for tracking page count bumped by shmem->sgt to avoid >> imbalanced page counter during of drm_gem_shmem_free() time. It's fragile >> to assume that populated shmem->pages at a freeing time means that the >> count was bumped by drm_gem_shmem_get_pages_sgt(), using a flag removes >> the ambiguity. >> >> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> >> --- >> drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ++- >> drivers/gpu/drm/lima/lima_gem.c | 1 + >> include/drm/drm_gem_shmem_helper.h | 7 +++++++ >> 3 files changed, 10 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c >> index 78d9cf2355a5..db20b9123891 100644 >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c >> @@ -152,7 +152,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) >> sg_free_table(shmem->sgt); >> kfree(shmem->sgt); >> } >> - if (shmem->pages) >> + if (shmem->got_sgt) >> drm_gem_shmem_put_pages(shmem); > > Can't we just move this drm_gem_shmem_put_pages() call in the > if (shmem->sgt) block? As you've seen in patch #1, the shmem->sgt may belong to imported dmabuf and pages aren't referenced in this case. I agree that the freeing code is confusing. The flags make it a better, not ideal. Though, the flags+comments solution is good enough to me. Please let me know if you have more suggestions, otherwise I'll add comment to the code and keep this patch for v16. BTW, I realized that the new flag wasn't placed properly in the Lima driver, causing unbalanced page count in the error path. Will correct it in v16.
On Sat, 2 Sep 2023 21:28:21 +0300 Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote: > On 8/28/23 13:55, Boris Brezillon wrote: > > On Sun, 27 Aug 2023 20:54:28 +0300 > > Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote: > > > >> Use separate flag for tracking page count bumped by shmem->sgt to avoid > >> imbalanced page counter during of drm_gem_shmem_free() time. It's fragile > >> to assume that populated shmem->pages at a freeing time means that the > >> count was bumped by drm_gem_shmem_get_pages_sgt(), using a flag removes > >> the ambiguity. > >> > >> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> > >> --- > >> drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ++- > >> drivers/gpu/drm/lima/lima_gem.c | 1 + > >> include/drm/drm_gem_shmem_helper.h | 7 +++++++ > >> 3 files changed, 10 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > >> index 78d9cf2355a5..db20b9123891 100644 > >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > >> @@ -152,7 +152,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > >> sg_free_table(shmem->sgt); > >> kfree(shmem->sgt); > >> } > >> - if (shmem->pages) > >> + if (shmem->got_sgt) > >> drm_gem_shmem_put_pages(shmem); > > > > Can't we just move this drm_gem_shmem_put_pages() call in the > > if (shmem->sgt) block? > > As you've seen in patch #1, the shmem->sgt may belong to imported dmabuf > and pages aren't referenced in this case. Unless I'm wrong, you're already in the if (!import_attach) branch here, so shmem->sgt should not be a dmabuf sgt. > > I agree that the freeing code is confusing. The flags make it a better, > not ideal. Though, the flags+comments solution is good enough to me. But what's the point of adding a flag when you can just do an if (!shmem->import_attach && shmem->sgt) check. At best, it just confuses people as to what these fields mean/are used for (especially when the field has such a generic name, when what you want is actually something like ->got_sgt_for_non_imported_object). But the most problematic aspect is that it adds fields to maintain, and those might end up being inconsistent with the object state because new/driver-specific code forgot to update them. > Please let me know if you have more suggestions, otherwise I'll add > comment to the code and keep this patch for v16. I'd definitely prefer adding the following helper static bool has_implicit_pages_ref(struct drm_gem_shmem_object *shmem) { return !shmem->import_attach && shmem->sgt; } which provides the same logic without adding a new field/flag. > > BTW, I realized that the new flag wasn't placed properly in the Lima > driver, causing unbalanced page count in the error path. Will correct it > in v16. See, that's the sort of subtle bugs I'm talking about. If the state is inferred from other fields that can't happen.
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 78d9cf2355a5..db20b9123891 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -152,7 +152,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) sg_free_table(shmem->sgt); kfree(shmem->sgt); } - if (shmem->pages) + if (shmem->got_sgt) drm_gem_shmem_put_pages(shmem); drm_WARN_ON(obj->dev, shmem->pages_use_count); @@ -687,6 +687,7 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_ if (ret) goto err_free_sgt; + shmem->got_sgt = true; shmem->sgt = sgt; return sgt; diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c index 4f9736e5f929..28602302c281 100644 --- a/drivers/gpu/drm/lima/lima_gem.c +++ b/drivers/gpu/drm/lima/lima_gem.c @@ -89,6 +89,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm) } *bo->base.sgt = sgt; + bo->base.got_sgt = true; if (vm) { ret = lima_vm_map_bo(vm, bo, old_size >> PAGE_SHIFT); diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h index ec70a98a8fe1..f87124629bb5 100644 --- a/include/drm/drm_gem_shmem_helper.h +++ b/include/drm/drm_gem_shmem_helper.h @@ -73,6 +73,13 @@ struct drm_gem_shmem_object { */ unsigned int vmap_use_count; + /** + * @got_sgt: + * + * True if SG table was retrieved using drm_gem_shmem_get_pages_sgt() + */ + bool got_sgt : 1; + /** * @imported_sgt: *
Use separate flag for tracking page count bumped by shmem->sgt to avoid imbalanced page counter during of drm_gem_shmem_free() time. It's fragile to assume that populated shmem->pages at a freeing time means that the count was bumped by drm_gem_shmem_get_pages_sgt(), using a flag removes the ambiguity. Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> --- drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ++- drivers/gpu/drm/lima/lima_gem.c | 1 + include/drm/drm_gem_shmem_helper.h | 7 +++++++ 3 files changed, 10 insertions(+), 1 deletion(-)