Per-thread allocation counters and limits

This tracks the amount of memory allocation by each thread in a
counter stored in the TSO.  Optionally, when the counter drops below
zero (it counts down), the thread can be sent an asynchronous
exception: AllocationLimitExceeded.  When this happens, given a small
additional limit so that it can handle the exception.  See
documentation in GHC.Conc for more details.

Allocation limits are similar to timeouts, but

  - timeouts use real time, not CPU time.  Allocation limits do not
    count anything while the thread is blocked or in foreign code.

  - timeouts don't re-trigger if the thread catches the exception,
    allocation limits do.

  - timeouts can catch non-allocating loops, if you use
    -fno-omit-yields.  This doesn't work for allocation limits.

I couldn't measure any impact on benchmarks with these changes, even
for nofib/smp.

1 files changed, 10 insertions, 0 deletions

diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c
index af1b2049f6..fb1e2ec07b 100644
--- a/rts/RtsFlags.c
+++ b/rts/RtsFlags.c
@@ -137,6 +137,7 @@ void initRtsFlagsDefaults(void)
 #else
     RtsFlags.GcFlags.heapBase           = 0;   /* means don't care */
 #endif
+    RtsFlags.GcFlags.allocLimitGrace    = (100*1024) / BLOCK_SIZE;
 
 #ifdef DEBUG
     RtsFlags.DebugFlags.scheduler       = rtsFalse;
@@ -402,6 +403,8 @@ usage_text[] = {
 "            +PAPI_EVENT   - collect papi preset event PAPI_EVENT",
 "            #NATIVE_EVENT - collect native event NATIVE_EVENT (in hex)",
 #endif
+"  -xq       The allocation limit given to a thread after it receives",
+"            an AllocationLimitExceeded exception. (default: 100k)",
 "",
 "RTS options may also be specified using the GHCRTS environment variable.",
 "",
@@ -1360,6 +1363,13 @@ error = rtsTrue;
 
                   /* The option prefix '-xx' is reserved for future extension.  KSW 1999-11. */
 
+                case 'q':
+                  OPTION_UNSAFE;
+                  RtsFlags.GcFlags.allocLimitGrace
+                      = decodeSize(rts_argv[arg], 3, BLOCK_SIZE, HS_INT_MAX)
+                          / BLOCK_SIZE;
+                  break;
+
                   default:
                     OPTION_SAFE;
                     errorBelch("unknown RTS option: %s",rts_argv[arg]);