optimize repopagestore_load_page_range

diff --git a/src/repopage.c b/src/repopage.c
index 0ad5323..99de972 100644 (file)
--- a/src/repopage.c
+++ b/src/repopage.c
@@ -578,7 +578,7 @@ repopagestore_load_page_range(Repopagestore *store, unsigned int pstart, unsigne
 /* Make sure all pages from PSTART to PEND (inclusive) are loaded,
    and are consecutive.  Return a pointer to the mapping of PSTART.  */
   unsigned char buf[REPOPAGE_BLOBSIZE];
-  unsigned int i;
+  unsigned int i, best;
 
   /* Quick check in case all pages are there already and consecutive.  */
   for (i = pstart; i <= pend; i++)
@@ -593,6 +593,10 @@ repopagestore_load_page_range(Repopagestore *store, unsigned int pstart, unsigne
   if (store->pagefd == -1)
     return 0;
 
+#ifdef DEBUG_PAGING
+  fprintf(stderr, "PAGE: want %d pages starting at %d\n", pend - pstart + 1, pstart);
+#endif
+
   /* Ensure that we can map the numbers of pages we need at all.  */
   if (pend - pstart + 1 > store->ncanmap)
     {
@@ -612,57 +616,58 @@ repopagestore_load_page_range(Repopagestore *store, unsigned int pstart, unsigne
      free (very cheap) or contains pages we search for anyway.  */
 
   {
-  /* Setup cost array.  */
-  unsigned int cost[store->ncanmap];
-  unsigned int best_cost;
-  unsigned int best;
-  unsigned int same_cost;
-  for (i = 0; i < store->ncanmap; i++)
-    {
-      unsigned int pnum = store->mapped[i];
-      if (pnum == 0)
-        cost[i] = 0;
-      else
-        {
-         Attrblobpage *p;
-         pnum--;
-         p = store->pages + pnum;
-         assert(p->mapped_at != -1);
-         if (pnum >= pstart && pnum <= pend)
-           cost[i] = 1;
-         else
-           cost[i] = 3;
-       }
-    }
+    unsigned int best_cost = -1;
+    unsigned int same_cost = 0;
+    unsigned int cost = 0;
+    int ii;
 
-  /* And search for cheapest space.  */
-  best_cost = -1;
-  best = 0;
-  same_cost = 0;
-  for (i = 0; i + pend - pstart < store->ncanmap; i++)
-    {
-      unsigned int c = cost[i];
-      unsigned int j;
-      for (j = 0; j < pend - pstart + 1; j++)
-        c += cost[i+j];
-      if (c < best_cost)
-        best_cost = c, best = i;
-      else if (c == best_cost)
-        same_cost++;
-      /* A null cost won't become better.  */
-      if (c == 0)
-        break;
-    }
-  /* If all places have the same cost we would thrash on slot 0.  Avoid
-     this by doing a round-robin strategy in this case.  */
-  if (same_cost == store->ncanmap - pend + pstart - 1)
-    best = store->rr_counter++ % (store->ncanmap - pend + pstart);
+    best = 0;
+    for (i = 0, ii = -(pend - pstart); i < store->ncanmap; i++, ii++)
+      {
+       unsigned int pnum = store->mapped[i];
+       if (pnum)
+         {
+           Attrblobpage *p = store->pages + --pnum;
+           assert(p->mapped_at != -1);
+           cost += pnum >= pstart && pnum <= pend ? 1 : 3;
+         }
+       if (ii < 0)
+         continue;     /* still need to accummulate cost */
+       if (cost < best_cost)
+         best_cost = cost, best = ii;
+       else if (cost == best_cost)
+         same_cost++;
+       if (!cost)
+         break;        /* it won't get any better */
+       /* now remove the cost of page ii again */
+       if (i == ii)
+         {
+           cost = 0;
+           continue;
+         }
+       pnum = store->mapped[ii];
+       if (pnum)
+         {
+           Attrblobpage *p = store->pages + --pnum;
+           assert(p->mapped_at != -1);
+           cost -= pnum >= pstart && pnum <= pend ? 1 : 3;
+         }
+      }
+
+#ifdef DEBUG_PAGING
+    fprintf(stderr, "PAGE: best %d at cost %d, same %d\n", best, best_cost, same_cost);
+#endif
+
+    /* If all places have the same cost we would thrash on slot 0.  Avoid
+       this by doing a round-robin strategy in this case.  */
+    if (same_cost == store->ncanmap - pend + pstart - 1)
+      best = store->rr_counter++ % (store->ncanmap - pend + pstart);
+  }
 
   /* So we want to map our pages from [best] to [best+pend-pstart].
      Use a very simple strategy, which doesn't make the best use of
      our resources, but works.  Throw away all pages in that range
-     (even ours) then copy around ours (in case they were outside the 
-     range) or read them in.  */
+     (even ours) then copy around ours or read them in.  */
   for (i = best; i < best + pend - pstart + 1; i++)
     {
       unsigned int pnum = store->mapped[i];
@@ -671,13 +676,26 @@ repopagestore_load_page_range(Repopagestore *store, unsigned int pstart, unsigne
             no need to evict it.  */
           && pnum != pstart + i - best)
        {
+         Attrblobpage *p;
          /* Evict this page.  */
 #ifdef DEBUG_PAGING
          fprintf(stderr, "PAGE: evict page %d from %d\n", pnum, i);
 #endif
-         cost[i] = 0;
          store->mapped[i] = 0;
          store->pages[pnum].mapped_at = -1;
+         /* check if we can copy the correct content */
+         p = store->pages + (pstart + i - best);
+         if (p->mapped_at != -1 && p->mapped_at != i * REPOPAGE_BLOBSIZE)
+           {
+             void *dest = store->blob_store + i * REPOPAGE_BLOBSIZE;
+#ifdef DEBUG_PAGING
+             fprintf(stderr, "PAGECOPY: %d from %d to %d\n", pstart + i - best, p->mapped_at / REPOPAGE_BLOBSIZE, i);
+#endif
+             memcpy(dest, store->blob_store + p->mapped_at, REPOPAGE_BLOBSIZE);
+             store->mapped[p->mapped_at / REPOPAGE_BLOBSIZE] = 0;
+             p->mapped_at = i * REPOPAGE_BLOBSIZE;
+             store->mapped[i] = pstart + i - best + 1;
+           }
        }
     }
 
@@ -692,7 +710,7 @@ repopagestore_load_page_range(Repopagestore *store, unsigned int pstart, unsigne
          if (p->mapped_at != pnum * REPOPAGE_BLOBSIZE)
            {
 #ifdef DEBUG_PAGING
-             fprintf(stderr, "PAGECOPY: %d to %d\n", i, pnum);
+             fprintf(stderr, "PAGECOPY: %d from %d to %d\n", i, p->mapped_at / REPOPAGE_BLOBSIZE, pnum);
 #endif
              /* Still mapped somewhere else, so just copy it from there.  */
              memcpy(dest, store->blob_store + p->mapped_at, REPOPAGE_BLOBSIZE);
@@ -736,7 +754,6 @@ repopagestore_load_page_range(Repopagestore *store, unsigned int pstart, unsigne
       store->mapped[pnum] = i + 1;
     }
   return store->blob_store + best * REPOPAGE_BLOBSIZE;
-  }
 }
 
 unsigned int