runtime: change minimum stack size to 2K.

It will be 8K on windows because it needs 4K for the OS.
Similarly, plan9 will be 4K.

On linux/amd64, reduces size of 100,000 goroutines
from ~819MB to ~245MB.

Update #7514

LGTM=dvyukov
R=golang-codereviews, dvyukov, khr, aram
CC=golang-codereviews
https://golang.org/cl/145790043

diff --git a/src/runtime/proc.c b/src/runtime/proc.c
index 0e677a9d28a8f35ce377fcf3a15a3afdc5ce7ca4..4282a145e11018253cf1f194e1e5fd8f4736f6ad 100644 (file)
--- a/src/runtime/proc.c
+++ b/src/runtime/proc.c
@@ -2162,11 +2162,11 @@ runtime·newproc1(FuncVal *fn, byte *argp, int32 narg, int32 nret, void *callerp
        siz = narg + nret;
        siz = (siz+7) & ~7;
 
-       // We could instead create a secondary stack frame
-       // and make it look like goexit was on the original but
-       // the call to the actual goroutine function was split.
+       // We could allocate a larger initial stack if necessary.
        // Not worth it: this is almost always an error.
-       if(siz > StackMin - 1024)
+       // 4*sizeof(uintreg): extra space added below
+       // sizeof(uintreg): caller's LR (arm) or return address (x86, in gostartcall).
+       if(siz >= StackMin - 4*sizeof(uintreg) - sizeof(uintreg))
                runtime·throw("runtime.newproc: function arguments too large for new goroutine");
 
        p = g->m->p;

diff --git a/src/runtime/stack.h b/src/runtime/stack.h
index b30e322166279d85b6354842846e0c86ff10adf9..f97dc4ed8db097dd8350256352eb9a7aaec51ba9 100644 (file)
--- a/src/runtime/stack.h
+++ b/src/runtime/stack.h
@@ -69,16 +69,19 @@ enum {
 #endif // Plan 9
 #endif // Windows
 
-       // The amount of extra stack to allocate beyond the size
-       // needed for the single frame that triggered the split.
-       StackExtra = 2048,
+       // The minimum size of stack used by Go code
+       StackMin = 2048,
 
-       // The minimum stack segment size to allocate.
-       // If the amount needed for the splitting frame + StackExtra
-       // is less than this number, the stack will have this size instead.
-       StackMin = 8192,
-       StackSystemRounded = StackSystem + (-StackSystem & (StackMin-1)),
-       FixedStack = StackMin + StackSystemRounded,
+       // The minimum stack size to allocate.
+       // The hackery here rounds FixedStack0 up to a power of 2.
+       FixedStack0 = StackMin + StackSystem,
+       FixedStack1 = FixedStack0 - 1,
+       FixedStack2 = FixedStack1 | (FixedStack1 >> 1),
+       FixedStack3 = FixedStack2 | (FixedStack2 >> 2),
+       FixedStack4 = FixedStack3 | (FixedStack3 >> 4),
+       FixedStack5 = FixedStack4 | (FixedStack4 >> 8),
+       FixedStack6 = FixedStack5 | (FixedStack5 >> 16),
+       FixedStack = FixedStack6 + 1,
 
        // Functions that need frames bigger than this use an extra
        // instruction to do the stack split check, to avoid overflow