On Wed, 2021-09-15 at 19:59 +0100, Matthew Auld wrote:
For cached objects we can allocate our pages directly in shmem. This should make it possible(in a later patch) to utilise the existing i915-gem shrinker code for such objects. For now this is still disabled.
Signed-off-by: Matthew Auld matthew.auld@intel.com Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Christian König christian.koenig@amd.com
drivers/gpu/drm/i915/gem/i915_gem_object.h | 8 + drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 14 +- drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 217 ++++++++++++++++++- -- 3 files changed, 209 insertions(+), 30 deletions(-)
...
} @@ -223,6 +349,10 @@ static bool i915_ttm_eviction_valuable(struct ttm_buffer_object *bo, { struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo); + if (place->mem_type == TTM_PL_SYSTEM && + bo->ttm && bo->ttm->page_flags & I915_TTM_TT_SHMEM) + return false;
Should we use ttm_bo_pin() / ttm_bo_unpin() to remove the bo from the TTM LRU lists when it's SHMEM populated, and change the above to a GEM_BUG_ON()?
/* Will do for now. Our pinned objects are still on TTM's LRU lists */ return i915_gem_object_evictable(obj); } @@ -316,9 +446,11 @@ static void i915_ttm_adjust_gem_after_move(struct drm_i915_gem_object *obj) i915_gem_object_set_cache_coherency(obj, cache_level); } -static void i915_ttm_purge(struct drm_i915_gem_object *obj) +static void i915_ttm_writeback(struct drm_i915_gem_object *obj) { struct ttm_buffer_object *bo = i915_gem_to_ttm(obj); + struct i915_ttm_tt *i915_tt = + container_of(bo->ttm, typeof(*i915_tt), ttm); struct ttm_operation_ctx ctx = { .interruptible = true, .no_wait_gpu = false, @@ -326,18 +458,52 @@ static void i915_ttm_purge(struct drm_i915_gem_object *obj) struct ttm_placement place = {}; int ret; - if (obj->mm.madv == __I915_MADV_PURGED) + if (!bo->ttm || !(bo->ttm->page_flags & I915_TTM_TT_SHMEM)) return; - /* TTM's purge interface. Note that we might be reentering. */ + i915_tt->backup = true; ret = ttm_bo_validate(bo, &place, &ctx);
It looks like writeback() becomes the backend's primary callback for shrinking, although for the shmem backend, this is put_pages(), and the writeback() callback is only called if needed to accelerate shmem's transfer of pages to the swap cache. It appears like this will break the shrinker reporting of shrunken pages?
Should we try to do the primary shrinking from the put_pages() callback instead, like the shmem backend? Although we'd have to allow NULL pages in put_pages() to account for evicted-to-shmem and adjust other backends if necessary.
- if (!ret) { - obj->write_domain = 0; - obj->read_domains = 0; - i915_ttm_adjust_gem_after_move(obj); - i915_ttm_free_cached_io_st(obj); - obj->mm.madv = __I915_MADV_PURGED; + i915_tt->backup = false; + if (ret) + return;
+ __shmem_writeback(obj->base.size, i915_tt->filp->f_mapping); +}