BufferProvider: devise a heuristic for buffer selection

- take into account how much memory will be wasted when
  using some allocation to satisfy a (smaller) allocation request
- furthermore prefer allocations used frequently in the past
- when an allocation is used, tag it with a score that also
  reflects this degree of waste
- select buffers with low score first for clean-up

src/vault/mem/local-mem-pool.hpp

@@ -13,6 +13,31 @@
 
 /** @file local-mem-pool.hpp
  ** A local cache of buffer allocations to facilitate reuse of memory in a worker.
+ ** Since the Lumiera Render Engine relies on scheduled jobs running concurrently,
+ ** it is essential to avoid any kind of locking that might prevent the calculations
+ ** from moving past each other. One crucial functionality that might lead to such
+ ** a subtle cross-wise obstruction is the handling of buffer memory allocations.
+ ** Each worker thread in the engine thus needs a (small) thread-local pool of
+ ** buffer allocations to handle all foreseeable allocation requests. Whenever
+ ** a render job starts, the information regarding a _maximal allocation footprint_
+ ** can be retrieved from the ProcNode, since this information is determined solely
+ ** by the expected call topology. Based on this information, additional memory
+ ** can be requested from a global buffer memory allocator; and while any new
+ ** allocation will take some time, the alloted buffer entries can be sent down
+ ** to the worker's local allocation pool through a lock-free queue, so that —
+ ** hopefully — these entries have already arrived at the point when the memory
+ ** is actually required from within the recursive Render Node `pull()` call.
+ ** 
+ ** LocalMemPool is responsible for receiving those memory provisions and for
+ ** managing and assigning available buffer blocks, drawing from the pool of
+ ** locally known allocations. For every new allocation request, an attempt
+ ** is made to find a best match within the available allotments of memory.
+ ** In the exceptional case however when no suitable prepared allocation
+ ** can be found locally, new memory must be acquired right away, since
+ ** render jobs are assumed to run through without blocking waits.
+ ** 
+ ** To avoid the hazard of the pool accumulating an increasing number of surplus
+ ** allocations over time, less frequently used blocks are culled using a heuristic.  
  ** 
  ** @see local-mem-pool-test.cpp
  ** @see local-buffer-store.hpp
@@ -51,6 +76,10 @@ namespace mem   {
     
     const size_t INQUEUE_SIZ = 30;   ///< initial size of the lock-free provision queue
     
+    const uint MATCH_SCORE    = 10;  ///< score to add when a buffer can be used to satisfy a request 
+    const uint UNUSABLE_MALUS = 2;   ///< reduce score whenever a buffer is too small to be useful
+    const double USAGE_WEIGHT = 0.9; ///< degree to which very frequent usage counteracts waste of memory
+    
   }//(End) config parameters and internals
   
   using std::move;
@@ -92,6 +121,8 @@ namespace mem   {
       InQueue inQueue_;
       BlockList blocks_;
       
+      int32_t maxScore_{1};
+      
     public:
       LocalMemPool()
         : inQueue_{INQUEUE_SIZ}
@@ -138,11 +169,26 @@ namespace mem   {
        *         \ref retrieve() an allocation will use available memory.
        *         There is no _handle_ to refer to some specific reservation.
        */
-      size_t
+      uint
       reserve (uint cnt, size_t sizRequest)
         {
           ingest();
-          return 0; ///////////////////////////////////////OOO
+          uint reserved{0};
+          for (Block& block : blocks_)
+            if (reserved >= cnt)
+              break;
+            else
+            if (not (block.used or block.resd)
+                and block.alloc.siz == sizRequest)
+              { // perfect match, reserve this allocation
+                block.resd = true;
+                ++reserved;
+              }
+          if (reserved < cnt)
+            { // now look for imperfect matches
+              TODO ("how to select best matches?");
+            }
+          return reserved;
         }
       
       /**
@@ -198,7 +244,6 @@ namespace mem   {
           else
             {
               ENSURE (not found->used);
-              found->score += 1; ///////////////////TODO
               found->resd = false;
               found->used = true;
               return found->alloc;
@@ -212,11 +257,26 @@ namespace mem   {
        * @return actual number of allocations removed from the pool.
        */
       template<class FUN> ////////TODO requires std::invocable<FUN,Buff*,size_t>
-      size_t
+      uint
       yield (uint cnt, size_t siz, FUN&& consumer)
         {
           ingest();
-          return 0;///////////////////////OOO
+          uint removed{0};
+          for (auto pos = blocks_.begin()
+              ; pos != blocks_.end()
+              ; ++pos)
+            if (cnt == 0)
+              break;
+            else
+            if (not pos->used
+                and siz == pos->alloc.siz)
+              {
+                consumer (pos->alloc.mem, pos->alloc.siz);
+                blocks_.erase (pos);
+                ++removed;
+                --cnt;
+              }
+          return removed;
         }
       
       /**
@@ -228,12 +288,29 @@ namespace mem   {
        * @return actual number of allocations removed from the pool.
        */
       template<class FUN> ////////TODO requires std::invocable<FUN,Buff*,size_t>
-      size_t
+      uint
       cleanup (double degree, FUN&& consumer)
         {
           ingest();
-          return 0;///////////////////////OOO
+          uint removed{0};
+          int32_t killLevel = degree * maxScore_;
+          for (auto pos = blocks_.begin()
+              ; pos != blocks_.end()
+              ; ++pos)
+            if (not (pos->used or pos->resd)
+                and pos->score <= killLevel)
+              { // send this allocation away and remove it from the pool
+                consumer (pos->alloc.mem, pos->alloc.siz);
+                blocks_.erase (pos);
+                ++removed;
               }
+            else
+              pos->score -= killLevel;
+           // recalibrate all score levels
+          maxScore_ -= killLevel;
+          return removed;
+        }
+      
       
     private:
       void
@@ -274,18 +351,32 @@ namespace mem   {
       selectBestMatch (size_t sizRequest)
         {
           Block* match{nullptr};
-          size_t waste(-1);
+          double bestSelector{0.0};
           for (Block& block : blocks_)
-            if (not block.used
+            if (not block.used)
-                and sizRequest <= block.alloc.siz)
               {
-                size_t wasted = block.alloc.siz - sizRequest;
+                if (sizRequest > block.alloc.siz)
-                if (wasted < waste)
+                  block.score -= UNUSABLE_MALUS;
+                else
                   {
-                    waste = wasted;
+                    double wasted = block.alloc.siz - sizRequest;
+                    double wasteScore = wasted / block.alloc.siz;
+                    double usageFact = block.score / maxScore_; 
+                    double selector = 1.0 - wasteScore * (1.0 - usageFact * USAGE_WEIGHT);
+                    if (selector > bestSelector)
+                      {
+                        bestSelector = selector;
                         match = &block;
                       }
                   }
+              }
+          if (match)
+            {
+              ENSURE (match->alloc.siz >= sizRequest);
+              match->score += int(MATCH_SCORE * (1 - (1 - double(sizRequest) / match->alloc.siz)));
+              if (match->score > maxScore_)       // reduce score by waste factor as malus
+                maxScore_ = match->score;
+            }
           return match;
         }
       
@@ -293,6 +384,8 @@ namespace mem   {
     };
   
   
+  
+  
   class PoolDiagnostic
     : util::MoveOnly
     {
@@ -316,6 +409,13 @@ namespace mem   {
           return std::ranges::count_if (memPool_.blocks_
                                        ,[siz](Block const& b){ return siz == b.alloc.siz; });
         }
+      
+      size_t
+      cntFree()
+        {
+          return std::ranges::count_if (memPool_.blocks_
+                                       ,[](Block const& b){ return not b.used; });
+        }
     };
   
   

tests/vault/mem/local-mem-pool-test.cpp

@@ -112,6 +112,28 @@ namespace test  {
           CHECK (pool.canServe(SIZ10));                        // query causes a scan and retrieval from the in-queu
           CHECK (watch(pool).cnt(SIZ10) == 1);
           CHECK (not watch(pool).isEmpty());
+          
+          pool.add (MEM2, SIZ20);
+          pool.add (MEM3, SIZ30);
+          CHECK (pool.canServe(SIZ20));
+          CHECK (pool.canServe(SIZ10));
+          CHECK (pool.size() == 3);
+          CHECK (watch(pool).cnt(SIZ10) == 1);
+          CHECK (watch(pool).cnt(SIZ20) == 1);
+          CHECK (watch(pool).cnt(SIZ30) == 1);
+          CHECK (watch(pool).cntFree()  == 3);
+          
+          auto [m1,s1] = pool.retrieve (SIZ20 -2);
+          CHECK (SIZ20 == s1);
+          CHECK (MEM2 == m1);
+          CHECK (watch(pool).cntFree()  == 2);
+          auto [m2,s2] = pool.retrieve (SIZ10);
+          CHECK (SIZ10 == s2);
+          CHECK (MEM1 == m2);
+          CHECK (watch(pool).cntFree()  == 1);
+          CHECK (pool.canServe(SIZ10));
+          CHECK (pool.canServe(SIZ20));
+          CHECK (pool.canServe(SIZ30));
         }
       
       

wiki/thinkPad.ichthyo.mm

@@ -145876,9 +145876,10 @@ StM_bind(Builder<R1> b1, Extension<R1,R2> extension)
 </node>
 <node BACKGROUND_COLOR="#eef0c5" COLOR="#990000" CREATED="1777050453251" ID="ID_1529547535" MODIFIED="1777066700207" TEXT="Implementieren">
 <icon BUILTIN="pencil"/>
-<node CREATED="1777052048904" ID="ID_1403107789" MODIFIED="1777052073352" TEXT="die Eingangs-Queue wird komplett (transparent) integriert">
+<node COLOR="#338800" CREATED="1777052048904" ID="ID_1403107789" MODIFIED="1777084853433" TEXT="die Eingangs-Queue wird komplett (transparent) integriert">
+<icon BUILTIN="button_ok"/>
 <node BACKGROUND_COLOR="#c8c0b6" COLOR="#435e98" CREATED="1777078419796" ID="ID_1966959598" MODIFIED="1777084265167" TEXT="verwende boost::lockfree::queue"/>
-<node BACKGROUND_COLOR="#f0d5c5" COLOR="#990033" CREATED="1777078428098" ID="ID_1939142827" MODIFIED="1777078435459" TEXT="ist das die richtige Wahl?">
+<node BACKGROUND_COLOR="#e0ceaa" COLOR="#470f69" CREATED="1777078428098" ID="ID_1939142827" MODIFIED="1777084838373" TEXT="ist das die richtige Wahl?">
 <icon BUILTIN="help"/>
 <node CREATED="1777078440070" ID="ID_885005752" MODIFIED="1777078470502" TEXT="verlangt &#xbb;trivial assignment&#xab; und Destructor"/>
 <node CREATED="1777078471365" ID="ID_769328039" MODIFIED="1777078487222" TEXT="hei&#xdf;t im Klartext: darf keine default-Initialiser haben">
@@ -145887,7 +145888,7 @@ StM_bind(Builder&lt;R1&gt; b1, Extension&lt;R1,R2&gt; extension)
 </node>
 <node COLOR="#435e98" CREATED="1777078635327" ID="ID_238173965" MODIFIED="1777084271658" TEXT="mu&#xdf; mir selber eine passende Struct bauen"/>
 </node>
-<node CREATED="1777078489787" ID="ID_1970735736" MODIFIED="1777084225822" TEXT="Vorteile">
+<node BACKGROUND_COLOR="#c8c0b6" COLOR="#435e98" CREATED="1777078489787" ID="ID_1970735736" MODIFIED="1777084845753" TEXT="Vorteile">
 <richcontent TYPE="NOTE"><html>
   <head/>
   <body>
@@ -145909,7 +145910,9 @@ StM_bind(Builder&lt;R1&gt; b1, Extension&lt;R1,R2&gt; extension)
 </node>
 </node>
 <node CREATED="1777052358645" ID="ID_1367907395" MODIFIED="1777052396869" TEXT="zum Aufr&#xe4;umen wird ein Empf&#xe4;nger-&#x3bb; &#xfc;bergeben"/>
-<node CREATED="1777052497154" ID="ID_1906132363" MODIFIED="1777052517239" TEXT="vorerst den default(-Heap)-Allokator f&#xfc;r alles verwenden"/>
+<node BACKGROUND_COLOR="#e0ceaa" COLOR="#620dbd" CREATED="1777052497154" ID="ID_1906132363" MODIFIED="1777084874533" TEXT="vorerst den default(-Heap)-Allokator f&#xfc;r alles verwenden">
+<icon BUILTIN="yes"/>
+</node>
 <node CREATED="1777073876105" ID="ID_1153882258" MODIFIED="1777073995987" TEXT="stelle fest: LinkedElements sind nicht gut geeignet">
 <richcontent TYPE="NOTE"><html>
   <head/>
@@ -145924,6 +145927,64 @@ StM_bind(Builder&lt;R1&gt; b1, Extension&lt;R1,R2&gt; extension)
 </node>
 <node CREATED="1777074521660" ID="ID_1763982951" MODIFIED="1777074532534" TEXT="grunds&#xe4;tzlich: gehe von einer kleinen Anzahl an Eintr&#xe4;gen aus"/>
 </node>
+<node BACKGROUND_COLOR="#eef0c5" COLOR="#990000" CREATED="1777159795008" ID="ID_851031995" MODIFIED="1777168836233" TEXT="Heuristik zum Aufr&#xe4;umen schaffen">
+<icon BUILTIN="pencil"/>
+<node CREATED="1777160636295" ID="ID_1174478817" MODIFIED="1777160642510" TEXT="gew&#xfc;nschter Effekt">
+<node CREATED="1777160710978" ID="ID_393248452" MODIFIED="1777160729106" TEXT="m&#xf6;glichst wenige und m&#xf6;glichst gut passende Buffer lokal halten"/>
+<node CREATED="1777162022979" ID="ID_763110420" MODIFIED="1777162035764" TEXT="Prio-1 ist stets den am besten passenden Buffer zu verwenden"/>
+<node CREATED="1777162072416" ID="ID_133387683" MODIFIED="1777162520272" TEXT="allerdings soll unter einem gewissen &#xbb;misfit&#xab;-Level dann MRU wichtiger werden">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      denn sonst h&#228;lt nach einiger Zeit jeder Pool eine Menge selten genutzter Buffer, obwohl man mit einem Bruchteil davon auch &#252;ber die Runden kommen k&#246;nnte
+    </p>
+  </body>
+</html>
+</richcontent>
+</node>
+</node>
+<node CREATED="1777162521383" ID="ID_215039061" MODIFIED="1777162527306" TEXT="Ansatz">
+<node CREATED="1777162528726" ID="ID_875736163" MODIFIED="1777162538808" TEXT="vergebe einen Score f&#xfc;r erfolgreichen Match"/>
+<node CREATED="1777162540196" ID="ID_1866543398" MODIFIED="1777162577399" TEXT="reduziere den Score f&#xfc;r zu gro&#xdf;en Buffer"/>
+<node CREATED="1777162589638" ID="ID_175029995" MODIFIED="1777162673190" TEXT="ziehe Punkte ab f&#xfc;r zu kleinen (unbauchbaren) Buffer"/>
+<node CREATED="1777162681518" ID="ID_1045190433" MODIFIED="1777162711729" TEXT="clean-up verwirft Buffer,,,">
+<node CREATED="1777162712892" ID="ID_1388888751" MODIFIED="1777162719520" TEXT="die nicht reserviert oder belegt sind"/>
+<node CREATED="1777162720405" ID="ID_718342875" MODIFIED="1777162812203" TEXT="deren Score prozentual unterhalb dem Max-Score liegen">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      wobei dieser Prozentsatz aus dem <font face="Monospaced" color="#683d3d">degree</font>&#160;- Parameter abgeleittet wird (mit umgekehrter Orientierung)
+    </p>
+  </body>
+</html>
+</richcontent>
+</node>
+</node>
+<node CREATED="1777162841060" ID="ID_1652390427" MODIFIED="1777162844852" TEXT="Punkts&#xe4;tze">
+<node CREATED="1777162851571" ID="ID_1498523122" MODIFIED="1777162858662" TEXT="+10 Punkte f&#xfc;r erfolgreichen Gebrauch"/>
+<node CREATED="1777162861786" ID="ID_990114851" MODIFIED="1777162887674" TEXT="bis zu 9 Punkte Abzug davon f&#xfc;r zu gro&#xdf;en Buffer"/>
+<node CREATED="1777162888442" ID="ID_416693693" MODIFIED="1777162913895" TEXT="jeder unbrauchbare Buffer bekommt einen Malus von -2"/>
+<node CREATED="1777162914715" ID="ID_577486589" MODIFIED="1777162923685" TEXT="Score kann nicht negativ werden"/>
+</node>
+</node>
+<node CREATED="1777162988481" ID="ID_1170538606" MODIFIED="1777162995671" TEXT="Implementierung">
+<node CREATED="1777162997152" ID="ID_833672862" MODIFIED="1777163012266" TEXT="berechne f&#xfc;r jeden Buffer einen waste-Score (0..9)"/>
+<node CREATED="1777163103258" ID="ID_1723954782" MODIFIED="1777163118028" TEXT="oder besser: eine matchQuality 1..10"/>
+<node CREATED="1777164416380" ID="ID_740262476" MODIFIED="1777164435189" TEXT="auf diese wende ich den allgemeinen Score graduell an">
+<node CREATED="1777164437720" ID="ID_712610709" MODIFIED="1777164452490" TEXT="und zwar mit steigendem Gewicht f&#xfc;r schlechteren Match"/>
+<node CREATED="1777164453966" ID="ID_1158139935" MODIFIED="1777164476724" TEXT="und als Malus f&#xfc;r seltener verwendete Buffer"/>
+</node>
+<node CREATED="1777164501370" ID="ID_1271851142" MODIFIED="1777164513738" TEXT="daraus ergibt sich ein transienter selectionScore"/>
+<node CREATED="1777164514849" ID="ID_489761092" MODIFIED="1777164525297" TEXT="und gew&#xe4;hlt wird nach maximalem selectionScore"/>
+<node CREATED="1777164528024" ID="ID_1047876896" MODIFIED="1777164541639" TEXT="dieser gew&#xe4;hlte Buffer bekommt dann einen Score-Update"/>
+</node>
+</node>
 </node>
 <node BACKGROUND_COLOR="#eef0c5" COLOR="#990000" CREATED="1777050457640" ID="ID_55967690" MODIFIED="1777084249904" TEXT="Dokumentieren per Test">
 <icon BUILTIN="pencil"/>