[PATCH v2 0/4] drm/xe: Prioritize BO eviction based on VM exec queue priority

[Matthew Brost <matthew.brost@intel.com>]

This series ties a BO's TTM LRU priority (i.e. how likely it is to be
picked for eviction/shrinking under memory pressure) to how userspace
is actually using the VM and BOs it belongs to, instead of treating
every BO the same.

The reasoning behind the heuristic:

 - Kernel BOs, and any BO not private to a single VM (no vm_id, e.g.
   shared/exported buffers), are given the highest priority so they
   are the least likely to be evicted -- these are foundational or
   shared resources.
 - BOs private to a VM are then prioritized based on the highest
   priority band userspace has assigned to any exec queue attached to
   that VM: a VM with a HIGH priority exec queue keeps its BOs at the
   highest priority (matching kernel/shared BOs), a VM with only
   NORMAL priority queues (or none yet) gets the next priority band
   down, and a VM with only LOW priority queues gets the band below
   that.
 - The lowest priority band is reserved exclusively for BOs (private
   or shared) that have no VMA mappings left anywhere. This lets
   userspace use an unbind as a signal of "drop this from my working
   set, but keep the backing store around in case I need it again" --
   the BO is retained, just made a preferred candidate for
   eviction/shrinking until it is rebound.

Patch 1 adds the accounting: a per-priority-band count of exec queues
attached to each user VM. Patch 2 introduces the actual heuristic and
uses it both to set a BO's initial priority at creation time and to
bulk re-prioritize a VM's existing private BOs when an exec queue is
added or removed. Patch 3 fixes up staleness that these earlier
mechanisms miss: BOs created before any exec queue exists, or bound
late via VM_BIND, and BOs not tied to a single VM that get demoted to
the lowest priority and then rebound. Patch 4 introduces the
lowest-priority demotion itself, applied when a BO loses its last VMA
mapping.

Matt

Matthew Brost (4):
  drm/xe: Track exec queue priority band counts for user VMs
  drm/xe: Re-prioritize VM's private BOs when adding an exec queue
  drm/xe: Fix up BO TTM priority for late VM binds
  drm/xe: Lower BO TTM priority to lowest when fully unmapped from VM

 drivers/gpu/drm/xe/xe_bo.c       |  18 ++-
 drivers/gpu/drm/xe/xe_bo.h       |   3 +-
 drivers/gpu/drm/xe/xe_bo_types.h |   3 +
 drivers/gpu/drm/xe/xe_dma_buf.c  |   2 +-
 drivers/gpu/drm/xe/xe_vm.c       | 205 +++++++++++++++++++++++++++++--
 drivers/gpu/drm/xe/xe_vm.h       |   1 +
 drivers/gpu/drm/xe/xe_vm_types.h |   7 ++
 7 files changed, 221 insertions(+), 18 deletions(-)

-- 
2.34.1