X not touching neighbour block works via setting MADV_RANDOM in last 1/4 of every block

wcfs/wcfs_test.py

@@ -459,10 +459,17 @@ class tFile:
             # works slow.
             # XXX -> make read(while-uploading) wait for uploading to complete
             # and only then return? (maybe it will help performance even in normal case)
-            mm.advise(blkmmap, (mm.MADV_NORMAL, mm.MADV_RANDOM)[blk%2])
+            #mm.advise(blkmmap, (mm.MADV_NORMAL, mm.MADV_RANDOM)[blk%2])
+            #mm.advise(blkmmap, (mm.MADV_RANDOM, mm.MADV_NORMAL)[blk%2])
             #mm.advise(blkmmap, mm.MADV_NORMAL)
             #mm.advise(blkmmap, mm.MADV_RANDOM)
 
+            # XXX vvv works - at the end of every block there is MAD_RANDOM
+            # range which is wider than RA window (XXX implicit) and so RA
+            # triggered before that, even if it overlaps with that last 1/4,
+            # don't trigger RA that overlaps with next block.
+            mm.advise(blkmmap[len(blkmmap)*3//4:], mm.MADV_RANDOM)
+
         tdb._files.add(t)
 
     def close(t):