#3364 Decrement bias only if there is 10prcnt free space

Instead of when there is any space.

indra/newview/llviewertexture.cpp

@@ -556,12 +556,13 @@ void LLViewerTexture::updateClass()
         // don't execute above until the slam to 1.5 has a chance to take effect
         sEvaluationTimer.reset();
 
-        // lower discard bias over time when free memory is available
-        if (sDesiredDiscardBias > 1.f && over_pct < 0.f)
+        // lower discard bias over time when at least 10% of budget is free
+        const F32 FREE_PERCENTAGE_TRESHOLD = -0.1f;
+        if (sDesiredDiscardBias > 1.f && over_pct < FREE_PERCENTAGE_TRESHOLD)
         {
             static LLCachedControl<F32> high_mem_discard_decrement(gSavedSettings, "RenderHighMemMinDiscardDecrement", .1f);
 
-            F32 decrement = high_mem_discard_decrement - llmin(over_pct, 0.f);
+            F32 decrement = high_mem_discard_decrement - llmin(over_pct - FREE_PERCENTAGE_TRESHOLD, 0.f);
             sDesiredDiscardBias -= decrement * gFrameIntervalSeconds;
         }
     }