[pypy-commit] stmgc c8-new-page-handling: we must not execute the STM part of the WB twice and make backup copies more than once

[Raemi]

Author: Remi Meier <remi.me...@inf.ethz.ch>
Branch: c8-new-page-handling
Changeset: r1437:4e523f10a999
Date: 2014-09-29 16:42 +0200
http://bitbucket.org/pypy/stmgc/changeset/4e523f10a999/

Log:    we must not execute the STM part of the WB twice and make backup
        copies more than once

diff --git a/c8/stm/core.c b/c8/stm/core.c
--- a/c8/stm/core.c
+++ b/c8/stm/core.c
@@ -429,7 +429,22 @@
     /* add to read set: */
     stm_read(obj);
 
-    /* create backup copy (this may cause several page faults XXX): */
+    /* XXX: add overflow number again? n^2 algorithm ahead... */
+    struct list_s *list = STM_PSEGMENT->modified_old_objects;
+    int i, c = list_count(list);
+    for (i = 0; i < c; i += 3) {
+        if (list->items[i] == (uintptr_t)obj) {
+            /* already executed WB once in this transaction. do GC
+               part again: */
+            obj->stm_flags &= ~GCFLAG_WRITE_BARRIER;
+            LIST_APPEND(STM_PSEGMENT->objects_pointing_to_nursery, obj);
+            return;
+        }
+    }
+
+    /* create backup copy (this may cause several page faults
+       XXX: do backup later and maybe allow for having NO_ACCESS
+       pages around anyway (kind of card marking)): */
     struct object_s *bk_obj = malloc(obj_size);
     memcpy(bk_obj, realobj, obj_size);
 
@@ -468,7 +483,6 @@
            update the shared page in stm_validate() except if it is the sole
            reader of it. But then we don't actually know which revision the 
page is at. */
         /* XXX this is a temporary solution I suppose */
-        int i;
         for (i = 0; i < NB_SEGMENTS; i++) {
             if (i == my_segnum)
                 continue;
@@ -708,12 +722,14 @@
                undo->backup + SLICE_OFFSET(undo->slice),
                SLICE_SIZE(undo->slice));
 
-        size_t obj_size = stmcb_size_rounded_up(undo->backup);
+        size_t obj_size = stmcb_size_rounded_up((struct 
object_s*)undo->backup);
+        dprintf(("reset_modified_from_backup_copies(%d): obj=%p off=%lu bk=%p 
obj_sz=%lu\n",
+                 segment_num, obj, SLICE_OFFSET(undo->slice), undo->backup, 
obj_size));
+
         if (obj_size - SLICE_OFFSET(undo->slice) <= 4096UL) {
             /* only free bk copy once (last slice): */
             free(undo->backup);
-            dprintf(("reset_modified_from_backup_copies(%d): obj=%p 
obj_sz=%lu\n",
-                     segment_num, obj, obj_size));
+            dprintf(("-> free(%p)\n", undo->backup));
         }
     }
 
diff --git a/c8/test/test_basic.py b/c8/test/test_basic.py
--- a/c8/test/test_basic.py
+++ b/c8/test/test_basic.py
@@ -810,3 +810,20 @@
         self.switch(1) # validate -> R2
 
         assert stm_get_char(lp_char_5, 384 - 1) == 'o'
+
+    def test_repeated_wb(self):
+        lp_char_5 = stm_allocate_old(384)
+
+        self.start_transaction()
+        stm_set_char(lp_char_5, 'i', 384 - 1, False)
+        stm_set_char(lp_char_5, 'i', HDR, False)
+
+        stm_minor_collect()
+
+        stm_set_char(lp_char_5, 'j', 384 - 1, False)
+        stm_set_char(lp_char_5, 'j', HDR, False)
+
+        self.abort_transaction()
+
+        self.check_char_everywhere(lp_char_5, '\0', offset=HDR)
+        self.check_char_everywhere(lp_char_5, '\0', offset=384-1)
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