revert use of mmap-go (#706)

We have a suspicion that when we switched to using the mmap-go library
it contributed to an issue where zoekt-webserver stops responding on
some linux versions. Our suspicion has something to do from us
hardcoding the page size to 4k to asking the kernel and how that
interacts with THP. Given we don't actually build for windows anymore,
we are partially reverting the mmap changes from
7424ac8

Test Plan: go test ./... on darwin. Then CI for linux testing.

go.mod

@@ -7,7 +7,6 @@ require (
 	github.com/andygrunwald/go-gerrit v0.0.0-20230628115649-c44fe2fbf2ca
 	github.com/bmatcuk/doublestar v1.3.4
 	github.com/dustin/go-humanize v1.0.1
-	github.com/edsrzf/mmap-go v1.1.0
 	github.com/felixge/fgprof v0.9.3
 	github.com/fsnotify/fsnotify v1.6.0
 	github.com/gfleury/go-bitbucket-v1 v0.0.0-20230626192437-8d7be5866751

go.sum

@@ -78,8 +78,6 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
-github.com/edsrzf/mmap-go v1.1.0 h1:6EUwBLQ/Mcr1EYLE4Tn1VdW1A4ckqCQWZBw8Hr0kjpQ=
-github.com/edsrzf/mmap-go v1.1.0/go.mod h1:19H/e8pUPLicwkyNgOykDXkJ9F0MHE+Z52B8EIth78Q=
 github.com/elazarl/goproxy v0.0.0-20221015165544-a0805db90819 h1:RIB4cRk+lBqKK3Oy0r2gRX4ui7tuhiZq2SuTtTCi0/0=
 github.com/elazarl/goproxy v0.0.0-20221015165544-a0805db90819/go.mod h1:Ro8st/ElPeALwNFlcTpWmkr6IoMFfkjXAvTHpevnDsM=
 github.com/emirpasic/gods v1.18.1 h1:FXtiHYKDGKCW2KzwZKx0iC0PQmdlorYgdFG9jPXJ1Bc=

indexfile_other.go

@@ -0,0 +1,62 @@
+// Copyright 2016 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !linux && !darwin
+// +build !linux,!darwin
+
+package zoekt
+
+import (
+	"fmt"
+	"os"
+)
+
+// NewIndexFile returns a new index file. The index file takes
+// ownership of the passed in file, and may close it.
+func NewIndexFile(f *os.File) (IndexFile, error) {
+	return &indexFileFromOS{f}, nil
+}
+
+type indexFileFromOS struct {
+	f *os.File
+}
+
+func (f *indexFileFromOS) Read(off, sz uint32) ([]byte, error) {
+	r := make([]byte, sz)
+	_, err := f.f.ReadAt(r, int64(off))
+	return r, err
+}
+
+func (f indexFileFromOS) Size() (uint32, error) {
+	fi, err := f.f.Stat()
+	if err != nil {
+		return 0, err
+	}
+
+	sz := fi.Size()
+
+	if sz >= maxUInt32 {
+		return 0, fmt.Errorf("overflow")
+	}
+
+	return uint32(sz), nil
+}
+
+func (f indexFileFromOS) Close() {
+	f.f.Close()
+}
+
+func (f indexFileFromOS) Name() string {
+	return f.f.Name()
+}

indexfile.go → indexfile_unix.go

@@ -12,24 +12,22 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux || darwin
+
 package zoekt
 
 import (
 	"fmt"
 	"log"
 	"os"
-	"runtime"
 
-	// cross-platform memory-mapped file package.
-	// Benchmarks the same speed as syscall/unix Mmap
-	// see https://github.com/peterguy/benchmark-mmap
-	mmap "github.com/edsrzf/mmap-go"
+	"golang.org/x/sys/unix"
 )
 
 type mmapedIndexFile struct {
 	name string
 	size uint32
-	data mmap.MMap
+	data []byte
 }
 
 func (f *mmapedIndexFile) Read(off, sz uint32) ([]byte, error) {
@@ -48,25 +46,11 @@ func (f *mmapedIndexFile) Size() (uint32, error) {
 }
 
 func (f *mmapedIndexFile) Close() {
-	if err := f.data.Unmap(); err != nil {
-		log.Printf("WARN failed to memory unmap %s: %v", f.name, err)
+	if err := unix.Munmap(f.data); err != nil {
+		log.Printf("WARN failed to Munmap %s: %v", f.name, err)
 	}
 }
 
-func bufferSize(f *mmapedIndexFile) int {
-	// On Unix/Linux, mmap likes to allocate memory in
-	// page-sized chunks, so round up to the OS page size.
-	// mmap will zero-fill the extra bytes.
-	// On Windows, the Windows API CreateFileMapping method
-	// requires a buffer the same size as the file.
-	bsize := int(f.size)
-	if runtime.GOOS != "windows" {
-		pagesize := os.Getpagesize() - 1
-		bsize = (bsize + pagesize) &^ pagesize
-	}
-	return bsize
-}
-
 // NewIndexFile returns a new index file. The index file takes
 // ownership of the passed in file, and may close it.
 func NewIndexFile(f *os.File) (IndexFile, error) {
@@ -86,10 +70,11 @@ func NewIndexFile(f *os.File) (IndexFile, error) {
 		size: uint32(sz),
 	}
 
-	r.data, err = mmap.MapRegion(f, bufferSize(r), mmap.RDONLY, 0, 0)
+	rounded := (r.size + 4095) &^ 4095
+	r.data, err = unix.Mmap(int(f.Fd()), 0, int(rounded), unix.PROT_READ, unix.MAP_SHARED)
 	if err != nil {
-		return nil, fmt.Errorf("NewIndexFile: unable to memory map %s: %w", f.Name(), err)
+		return nil, err
 	}
 
-	return r, nil
+	return r, err
 }