Quoting Jason Gunthorpe (2020-06-24 20:21:16) > On Wed, Jun 24, 2020 at 08:14:17PM +0100, Chris Wilson wrote: > > A general rule of thumb is that shrinkers should be fast and effective. > > They are called from direct reclaim at the most incovenient of times when > > the caller is waiting for a page. If we attempt to reclaim a page being > > pinned for active dma [pin_user_pages()], we will incur far greater > > latency than a normal anonymous page mapped multiple times. Worse the > > page may be in use indefinitely by the HW and unable to be reclaimed > > in a timely manner. > > A pinned page can't be migrated, discarded or swapped by definition - > it would cause data corruption. > > So, how do things even get here and/or work today at all? I think the > explanation is missing something important. [<0>] userptr_mn_invalidate_range_start+0xa7/0x170 [i915] [<0>] __mmu_notifier_invalidate_range_start+0x110/0x150 [<0>] try_to_unmap_one+0x790/0x870 [<0>] rmap_walk_file+0xe9/0x230 [<0>] rmap_walk+0x27/0x30 [<0>] try_to_unmap+0x89/0xc0 [<0>] shrink_page_list+0x88a/0xf50 [<0>] shrink_inactive_list+0x137/0x2f0 [<0>] shrink_lruvec+0x4ec/0x5f0 [<0>] shrink_node+0x15d/0x410 [<0>] try_to_free_pages+0x17f/0x430 [<0>] __alloc_pages_slowpath+0x2ab/0xcc0 [<0>] __alloc_pages_nodemask+0x1ad/0x1e0 [<0>] new_slab+0x2d8/0x310 [<0>] ___slab_alloc.constprop.0+0x288/0x520 [<0>] __slab_alloc.constprop.0+0xd/0x20 [<0>] kmem_cache_alloc_trace+0x1ad/0x1c0 and that hits an active pin_user_pages object. Is there some information that would help in particular? -Chris
