1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
|
// Copyright 2019 The gVisor Authors.
//
// 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.
// Package hostmm provides tools for interacting with the host Linux kernel's
// virtual memory management subsystem.
package hostmm
import (
"fmt"
"os"
"path"
"gvisor.dev/gvisor/pkg/eventfd"
"gvisor.dev/gvisor/pkg/log"
)
// NotifyCurrentMemcgPressureCallback requests that f is called whenever the
// calling process' memory cgroup indicates memory pressure of the given level,
// as specified by Linux's Documentation/cgroup-v1/memory.txt.
//
// If NotifyCurrentMemcgPressureCallback succeeds, it returns a function that
// terminates the requested memory pressure notifications. This function may be
// called at most once.
func NotifyCurrentMemcgPressureCallback(f func(), level string) (func(), error) {
cgdir, err := currentCgroupDirectory("memory")
if err != nil {
return nil, err
}
pressurePath := path.Join(cgdir, "memory.pressure_level")
pressureFile, err := os.Open(pressurePath)
if err != nil {
return nil, err
}
defer pressureFile.Close()
eventControlPath := path.Join(cgdir, "cgroup.event_control")
eventControlFile, err := os.OpenFile(eventControlPath, os.O_WRONLY, 0)
if err != nil {
return nil, err
}
defer eventControlFile.Close()
eventFD, err := eventfd.Create()
if err != nil {
return nil, err
}
// Don't use fmt.Fprintf since the whole string needs to be written in a
// single unix.
eventControlStr := fmt.Sprintf("%d %d %s", eventFD.FD(), pressureFile.Fd(), level)
if n, err := eventControlFile.Write([]byte(eventControlStr)); n != len(eventControlStr) || err != nil {
eventFD.Close()
return nil, fmt.Errorf("error writing %q to %s: got (%d, %v), wanted (%d, nil)", eventControlStr, eventControlPath, n, err, len(eventControlStr))
}
log.Debugf("Receiving memory pressure level notifications from %s at level %q", pressurePath, level)
const sizeofUint64 = 8
// The most significant bit of the eventfd value is set by the stop
// function, which is practically unambiguous since it's not plausible for
// 2**63 pressure events to occur between eventfd reads.
const stopVal = 1 << 63
stopCh := make(chan struct{})
go func() { // S/R-SAFE: f provides synchronization if necessary
for {
val, err := eventFD.Read()
if err != nil {
panic(fmt.Sprintf("failed to read from memory pressure level eventfd: %v", err))
}
if val >= stopVal {
// Assume this was due to the notifier's "destructor" (the
// function returned by NotifyCurrentMemcgPressureCallback
// below) being called.
eventFD.Close()
close(stopCh)
return
}
f()
}
}()
return func() {
eventFD.Write(stopVal)
<-stopCh
}, nil
}
|
