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

[Thomas Hellström]

On Mon, 2025-08-04 at 19:29 +0000, Summers, Stuart wrote:
> On Mon, 2025-08-04 at 10:10 +0200, Thomas Hellström wrote:
> > When the xe buffer-object shrinker allows GPU waits and write-back,
> > (typically from kswapd), perform multilpe passes, skipping
> 
> /s/multilpe/multiple/
> 
> > 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.
> > 
> > Closes:
> > https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5557#note_3035136
> > Fixes: 00c8efc3180f ("drm/xe: Add a shrinker for xe bos")
> > Cc: <stable at vger.kernel.org> # v6.15+
> > Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> 
> I see the reported requested:
> Reported-by: melvyn <melvyn2 at dnsense.pub>
> 
> > ---
> >  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..bc3439bd4450 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.
> > + */
> > +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)
> 
> Why not include this in the !ctx->no_wait_gpu condition above? If
> ctx-
> > no_wait_gpu was passed in as true here, we're just checking scanned
> > >=
> to_scan twice in a row with the same values.
> 
> Otherwise the patch lgtm.

Thanks for the review. Will fix.
/Thomas

> 
> Thanks,
> Stuart
> 
> > +               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)
>