Re: [PATCH v2] drm/xe: Defer buffer object shrinker write-backs and GPU waits

On 05/08/2025 08:48, Thomas Hellström wrote:

When the xe buffer-object shrinker allows GPU waits and write-back, (typically from kswapd), perform multiple passes, skipping subsequent passes if the shrinker number of scanned objects target is reached.

1. Without GPU waits and write-back
2. Without write-back
3. With both GPU-waits and write-back

This is to avoid stalls and costly write- and readbacks unless they are really necessary.

v2:

• Don't test for scan completion twice. (Stuart Summers)
• Update tags.

Reported-by: melvyn melvyn2@dnsense.pub Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5557 Cc: Summers Stuart stuart.summers@intel.com Fixes: 00c8efc3180f ("drm/xe: Add a shrinker for xe bos") Cc: stable@vger.kernel.org # v6.15+ Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com

---

drivers/gpu/drm/xe/xe_shrinker.c | 51 +++++++++++++++++++++++++++++--- 1 file changed, 47 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_shrinker.c b/drivers/gpu/drm/xe/xe_shrinker.c index 1c3c04d52f55..90244fe59b59 100644 --- a/drivers/gpu/drm/xe/xe_shrinker.c +++ b/drivers/gpu/drm/xe/xe_shrinker.c @@ -54,10 +54,10 @@ xe_shrinker_mod_pages(struct xe_shrinker *shrinker, long shrinkable, long purgea write_unlock(&shrinker->lock); } -static s64 xe_shrinker_walk(struct xe_device *xe,

• 	    struct ttm_operation_ctx *ctx,
  

• 	    const struct xe_bo_shrink_flags flags,
  

• 	    unsigned long to_scan, unsigned long *scanned)
  

+static s64 __xe_shrinker_walk(struct xe_device *xe,

• 	      struct ttm_operation_ctx *ctx,
  

• 	      const struct xe_bo_shrink_flags flags,
  

• 	      unsigned long to_scan, unsigned long *scanned)
  

  { unsigned int mem_type; s64 freed = 0, lret;

@@ -93,6 +93,48 @@ static s64 xe_shrinker_walk(struct xe_device *xe, return freed; } +/*

• • Try shrinking idle objects without writeback first, then if not sufficient,
• • try also non-idle objects and finally if that's not sufficient either,
• • add writeback. This avoids stalls and explicit writebacks with light or
• • moderate memory pressure.

Just one question here, with writeback=false it doesn't really influence which objects are chosen for shrinking, unlike with no_wait_gpu, right? Will having another pass just with writeback=true yield anything different, assuming here that the previous two passes would have already hoovered ~everything up that was a possible candidate, so this pass won't really find anything in practice? If so, does that also mean we never really end up using the writeback=true behaviour any more?

• */

+static s64 xe_shrinker_walk(struct xe_device *xe,

• 	    struct ttm_operation_ctx *ctx,
  

• 	    const struct xe_bo_shrink_flags flags,
  

• 	    unsigned long to_scan, unsigned long *scanned)
  

+{

• bool no_wait_gpu = true;
• struct xe_bo_shrink_flags save_flags = flags;
• s64 lret, freed;
• swap(no_wait_gpu, ctx->no_wait_gpu);
• save_flags.writeback = false;
• lret = __xe_shrinker_walk(xe, ctx, save_flags, to_scan, scanned);
• swap(no_wait_gpu, ctx->no_wait_gpu);
• if (lret < 0 || *scanned >= to_scan)

• return lret;
  

• freed = lret;
• if (!ctx->no_wait_gpu) {

• lret = __xe_shrinker_walk(xe, ctx, save_flags, to_scan, scanned);
  

• if (lret < 0)
  

• 	return lret;
  

• freed += lret;
  

• if (*scanned >= to_scan)
  

• 	return freed;
  

• }
• if (flags.writeback) {

• lret = __xe_shrinker_walk(xe, ctx, flags, to_scan, scanned);
  

• if (lret < 0)
  

• 	return lret;
  

• freed += lret;
  

• }
• return freed;

+}

• static unsigned long xe_shrinker_count(struct shrinker *shrink, struct shrink_control *sc) {

@@ -199,6 +241,7 @@ static unsigned long xe_shrinker_scan(struct shrinker *shrink, struct shrink_con runtime_pm = xe_shrinker_runtime_pm_get(shrinker, true, 0, can_backup); shrink_flags.purge = false;

• lret = xe_shrinker_walk(shrinker->xe, &ctx, shrink_flags, nr_to_scan, &nr_scanned); if (lret >= 0)