memory accounting: blame the parent instead of the child

svn: r12853

collects/scheme/sandbox.ss

@@ -312,7 +312,7 @@
          ;; time limit
          (when sec
            (let ([t (current-thread)])
-             (thread (lambda () (sleep sec) (set! r 'time) (kill-thread t)))))
+             (thread (lambda () (unless (sync/timeout sec t) (set! r 'time)) (kill-thread t)))))
          (set! r (with-handlers ([void (lambda (e) (list raise e))])
                    (call-with-values thunk (lambda vs (list* values vs))))))
        ;; The thread might be killed by the timer thread, so don't let

collects/scribblings/reference/custodians.scrbl

@@ -57,19 +57,19 @@ or indirectly). If @scheme[cust] is not strictly subordinate to
 
 @defproc[(custodian-memory-accounting-available?) boolean?]{
 
-Returns @scheme[#t] if PLT Scheme is compiled with support for
-per-custodian memory accounting, @scheme[#f] otherwise.
-
 @margin-note{Memory accounting is normally available in PLT Scheme 3m,
 which is the main variant of PLT Scheme, and not normally available in
-PLT Scheme CGC.}}
+PLT Scheme CGC.}
+
+Returns @scheme[#t] if PLT Scheme is compiled with support for
+per-custodian memory accounting, @scheme[#f] otherwise.}
 
 @defproc[(custodian-require-memory [limit-cust custodian?]
                                    [need-amt exact-nonnegative-integer?]
                                    [stop-cust custodian?]) void?]{
 
-Registers a require check if PLT Scheme is compiled with support for
+Registers a required-memory check if PLT Scheme is compiled with
-per-custodian memory accounting, otherwise the
+support for per-custodian memory accounting, otherwise the
 @exnraise[exn:fail:unsupported].
 
 If a check is registered, and if PLT Scheme later reaches a state after
@@ -81,8 +81,8 @@ trigger some shutdown, then @scheme[stop-cust] is shut down.}
                                  [limit-amt exact-nonnegative-integer?]
                                  [stop-cust custodian? limit-cust]) void?]{
 
-Registers a limit check if PLT Scheme is compiled with support for
+Registers a limited-memory check if PLT Scheme is compiled with
-per-custodian memory accounting, otherwise the
+support for per-custodian memory accounting, otherwise the
 @exnraise[exn:fail:unsupported].
 
 If a check is registered, and if PLT Scheme later reaches a state
@@ -93,7 +93,10 @@ after garbage collection (see @secref["gc-model"]) where
 @margin-note{A custodian's limit is checked only after a garbage
              collection, except that it may also be checked during
              certain large allocations that are individually larger
-             than the custodian's limit.}
+             than the custodian's limit. A single garbage collection
+             may shut down multiple custodians, even if shutting down
+             only one of the custodians would have reduced memory use
+             for other custodians.}
 
 For reliable shutdown, @scheme[limit-amt] for
 @scheme[custodian-limit-memory] must be much lower than the total

collects/scribblings/reference/eval-model.scrbl

@@ -801,7 +801,9 @@ object is reachable from two custodians where neither is an ancestor
 of the other, an object is arbitrarily charged to one of the other,
 and the choice can change after each collection; objects reachable
 from both a custodian and its descendant, however, are reliably
-charged to the descendant.  Reachability for per-custodian accounting
+charged to the custodian and not to the descendants, unless the
-does not include weak references, references to threads managed by
+custodian can reach the objects only through a descendant custodian or
-non-descendant custodians, references to non-descendant custodians, or
+a descendant's thread.  Reachability for per-custodian accounting does
-references to custodian boxes for non-descendant custodians.
+not include weak references, references to threads managed by other
+custodians, references to other custodians, or references to custodian
+boxes for other custodians.

doc/release-notes/mzscheme/HISTORY.txt

@@ -1,3 +1,6 @@
+Version 4.1.3.6
+Memory accounting changed to bias charges to parent instead of children
+
 Version 4.1.3.3
 Added compile-context-preservation-enabled
 Added exception-backtrace support for x86_84+JIT

src/mzscheme/gc2/Makefile.in

@@ -312,7 +312,7 @@ main.@LTO@: $(XSRCDIR)/main.c
 	$(CC) $(CFLAGS) -c $(XSRCDIR)/main.c -o main.@LTO@
 
 gc2.@LTO@: $(srcdir)/gc2.c $(srcdir)/newgc.c $(srcdir)/gc2.h \
-			 $(srcdir)/newgc.h $(srcdir)/blame_the_child.c \
+			 $(srcdir)/newgc.h $(srcdir)/mem_account.c \
 			 $(srcdir)/sighand.c \
        $(srcdir)/vm_osx.c $(srcdir)/vm_mmap.c $(srcdir)/vm_osk.c $(srcdir)/vm.c\
        $(srcdir)/vm_memalign.c $(srcdir)/alloc_cache.c \

src/mzscheme/gc2/mem_account.c

@@ -1,11 +1,11 @@
 /*****************************************************************************/
-/* blame-the-child accounting                                                */
+/* memory accounting                                                         */
 /*****************************************************************************/
 #ifdef NEWGC_BTC_ACCOUNT
 
 #include "../src/schpriv.h"
 /* BTC_ prefixed functions are called by newgc.c */
-/* btc_ prefixed functions are internal to blame_the_child.c */
+/* btc_ prefixed functions are internal to mem_account.c */
 
 static const int btc_redirect_thread    = 511;
 static const int btc_redirect_custodian = 510;
@@ -430,13 +430,7 @@ static void BTC_do_accounting(NewGC *gc)
       if(owner_table[i])
         owner_table[i]->memory_use = 0;
 
-    /* the end of the custodian list is where we want to start */
+    /* walk forward for the order we want (blame parents instead of children) */
-    while(SCHEME_PTR1_VAL(box)) {
-      cur = (Scheme_Custodian*)SCHEME_PTR1_VAL(box);
-      box = cur->global_next;
-    }
-
-    /* walk backwards for the order we want */
     while(cur) {
       int owner = custodian_to_owner_set(gc, cur);
 
@@ -448,7 +442,7 @@ static void BTC_do_accounting(NewGC *gc)
       GCDEBUG((DEBUGOUTF, "Propagating accounting marks\n"));
       propagate_accounting_marks(gc);
 
-      box = cur->global_prev; cur = box ? SCHEME_PTR1_VAL(box) : NULL;
+      box = cur->global_next; cur = box ? SCHEME_PTR1_VAL(box) : NULL;
     }
 
     gc->in_unsafe_allocation_mode = 0;

src/mzscheme/gc2/newgc.c

@@ -93,7 +93,7 @@ inline static int is_master_gc(NewGC *gc) {
 /* particular collector you want.                                            */
 /*****************************************************************************/
 
-/* This turns on blame-the-child automatic memory accounting */
+/* This turns on automatic memory accounting */
 /* #define NEWGC_BTC_ACCOUNT */
 /* #undef NEWGC_BTC_ACCOUNT */
 
@@ -1365,11 +1365,11 @@ inline static void reset_pointer_stack(void)
 }
 
 /*****************************************************************************/
-/* BLAME THE CHILD                                                           */
+/* MEMORY ACCOUNTING                                                         */
 /*****************************************************************************/
 
 #ifdef NEWGC_BTC_ACCOUNT
-# include "blame_the_child.c"
+# include "mem_account.c"
 #else
 # define clean_up_thread_list() /* */
 #endif