cmd/link: reduce the size of Reloc struct

For linking large binaries, the slice of Relocs consumes a large
amount of memory. We can reduce this memory consumption by
shrinking the size of the Reloc struct. This CL moves the fields
used only in external linking or only on PPC64 and S390X to a
lazily initialized side struct.

Linking k8s.io/kubernetes/cmd/kube-apiserver on Linux/AMD64,
before:
inuse_space 1240.25MB total
438.11MB 35.32% 35.32%   438.11MB 35.32%  cmd/link/internal/objfile.(*objReader).readSlices

after:
inuse_space 1123.39MB total
306.85MB 27.31% 55.03%   306.85MB 27.31%  cmd/link/internal/objfile.(*objReader).readSlices

Under GOGC=5 (to simulate system under memory pressure), the max
RSS reduces from ~2.05G to ~1.83G. Even with external linking the
max RSS doesn't increase.

Change-Id: I9bb8a8effaed24a8b3c4b1cfb93e6992b8740f91
Reviewed-on: https://go-review.googlesource.com/c/go/+/173437
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/internal/objabi/reloctype.go b/src/cmd/internal/objabi/reloctype.go
index f619e017d8b86b55e79100e7122bc7d52fe6d276..94d5469d9cec92d92a33b291400eaa3115e213c5 100644 (file)
--- a/src/cmd/internal/objabi/reloctype.go
+++ b/src/cmd/internal/objabi/reloctype.go
@@ -30,7 +30,7 @@
 
 package objabi
 
-type RelocType int32
+type RelocType int16
 
 //go:generate stringer -type=RelocType
 const (

diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 3b551db85305f9bb14a63bf1a7ca9174848558dc..8e35f5c9dc88f4622ffa195758ead7d2a711da69 100644 (file)
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -189,13 +189,19 @@ func relocsym(ctxt *Link, s *sym.Symbol) {
                        Errorf(s, "unreachable sym in relocation: %s", r.Sym.Name)
                }
 
+               if ctxt.LinkMode == LinkExternal {
+                       r.InitExt()
+               }
+
                // TODO(mundaym): remove this special case - see issue 14218.
                if ctxt.Arch.Family == sys.S390X {
                        switch r.Type {
                        case objabi.R_PCRELDBL:
+                               r.InitExt()
                                r.Type = objabi.R_PCREL
                                r.Variant = sym.RV_390_DBL
                        case objabi.R_CALL:
+                               r.InitExt()
                                r.Variant = sym.RV_390_DBL
                        }
                }
@@ -499,8 +505,11 @@ func relocsym(ctxt *Link, s *sym.Symbol) {
                        o = r.Add
                }
 
-               if r.Variant != sym.RV_NONE {
-                       o = thearch.Archrelocvariant(ctxt, r, s, o)
+               if ctxt.Arch.Family == sys.PPC64 || ctxt.Arch.Family == sys.S390X {
+                       r.InitExt()
+                       if r.Variant != sym.RV_NONE {
+                               o = thearch.Archrelocvariant(ctxt, r, s, o)
+                       }
                }
 
                if false {

diff --git a/src/cmd/link/internal/ppc64/asm.go b/src/cmd/link/internal/ppc64/asm.go
index 365a45ec135c40d4afb6925601fb34bf7f75399a..c315b4bfc2d4415df8faab2ebf4bd38dd2e6283c 100644 (file)
--- a/src/cmd/link/internal/ppc64/asm.go
+++ b/src/cmd/link/internal/ppc64/asm.go
@@ -272,6 +272,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
 }
 func addelfdynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
        targ := r.Sym
+       r.InitExt()
 
        switch r.Type {
        default:

diff --git a/src/cmd/link/internal/s390x/asm.go b/src/cmd/link/internal/s390x/asm.go
index 85403774004fef435b7e26f8002811da91e8963a..040c5737058dcfae6c610830cf00c5ba9a6391fc 100644 (file)
--- a/src/cmd/link/internal/s390x/asm.go
+++ b/src/cmd/link/internal/s390x/asm.go
@@ -104,6 +104,7 @@ func gentext(ctxt *ld.Link) {
 
 func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
        targ := r.Sym
+       r.InitExt()
 
        switch r.Type {
        default:

diff --git a/src/cmd/link/internal/sym/reloc.go b/src/cmd/link/internal/sym/reloc.go
index 9c862f109d76d3f6a0e149670060a250c83be7d4..4809db8c800506224bb3dccaa8bc3db345adb753 100644 (file)
--- a/src/cmd/link/internal/sym/reloc.go
+++ b/src/cmd/link/internal/sym/reloc.go
@@ -22,15 +22,27 @@ import (
 //
 // Some relocations are created by cmd/link.
 type Reloc struct {
-       Off     int32            // offset to rewrite
-       Siz     uint8            // number of bytes to rewrite, 1, 2, or 4
-       Done    bool             // set to true when relocation is complete
-       Variant RelocVariant     // variation on Type
-       Type    objabi.RelocType // the relocation type
-       Add     int64            // addend
-       Xadd    int64            // addend passed to external linker
-       Sym     *Symbol          // symbol the relocation addresses
-       Xsym    *Symbol          // symbol passed to external linker
+       Off       int32            // offset to rewrite
+       Siz       uint8            // number of bytes to rewrite, 1, 2, or 4
+       Done      bool             // set to true when relocation is complete
+       Type      objabi.RelocType // the relocation type
+       Add       int64            // addend
+       Sym       *Symbol          // symbol the relocation addresses
+       *relocExt                  // extra fields (see below), may be nil, call InitExt before use
+}
+
+// relocExt contains extra fields in Reloc that are used only in
+// certain cases.
+type relocExt struct {
+       Xadd    int64        // addend passed to external linker
+       Xsym    *Symbol      // symbol passed to external linker
+       Variant RelocVariant // variation on Type, currently used only on PPC64 and S390X
+}
+
+func (r *Reloc) InitExt() {
+       if r.relocExt == nil {
+               r.relocExt = new(relocExt)
+       }
 }
 
 // RelocVariant is a linker-internal variation on a relocation.

diff --git a/src/cmd/link/internal/sym/symbol.go b/src/cmd/link/internal/sym/symbol.go
index 88a28f5b9960886b91a66d098c7e4d41a573b43f..d115a3326f438870492ea85f10434b3d5987aff6 100644 (file)
--- a/src/cmd/link/internal/sym/symbol.go
+++ b/src/cmd/link/internal/sym/symbol.go
@@ -211,6 +211,9 @@ func (s *Symbol) AddPCRelPlus(arch *sys.Arch, t *Symbol, add int64) int64 {
        r.Add = add
        r.Type = objabi.R_PCREL
        r.Siz = 4
+       if arch.Family == sys.S390X || arch.Family == sys.PPC64 {
+               r.InitExt()
+       }
        if arch.Family == sys.S390X {
                r.Variant = RV_390_DBL
        }