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Andrei VaginandgVisor bot
890a66acd4
FDTable.descriptorTable is a slice of unsafe.Pointer-s and its maximum length is MaxInt32. It requires up to 16GB of memory. A process can use just a few descriptors but sets one or more of them to high numbers. In this case, FDTable.descriptorTable is extended to the maximum size. The problem here is that go-runtime zeros memory regions when they are reused. In the case of fdtable, the memory region is 16GB, so it is a time consuming operation. Second, it forces the kernel to allocate physical pages to the entire region. This change adds another level to descriptorTable, so the first level is a slice of buckets where each bucket is a slice of descriptors. The bucket size is fixed to 512 entries to fit one page. Before: BenchmarkFDLookupAndDecRef-12 50834290 23.70 ns/op BenchmarkCreateWithMaxFD-12 2 7194873988 ns/op BenchmarkFDLookupAndDecRefConcurrent-12 23775555 49.68 ns/op BenchmarkTableLookup-12 412888780 2.835 ns/op BenchmarkTableMapLookup-12 87944782 12.84 ns/op After: BenchmarkFDLookupAndDecRef-12 46229940 25.03 ns/op BenchmarkCreateWithMaxFD-12 13 82573899 ns/op BenchmarkFDLookupAndDecRefConcurrent-12 21889380 54.13 ns/op BenchmarkTableLookup-12 415851230 2.821 ns/op BenchmarkTableMapLookup-12 97236267 11.89 ns/op Reported-by: [email protected] PiperOrigin-RevId: 539138632
55 lines
1.5 KiB
Go
55 lines
1.5 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package seqatomic doesn't exist. This file must be instantiated using the
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// go_template_instance rule in tools/go_generics/defs.bzl.
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package seqatomic
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import (
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"sync/atomic"
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"unsafe"
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)
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// Value is a required type parameter.
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type Value struct{}
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// An AtomicPtr is a pointer to a value of type Value that can be atomically
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// loaded and stored. The zero value of an AtomicPtr represents nil.
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//
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// Note that copying AtomicPtr by value performs a non-atomic read of the
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// stored pointer, which is unsafe if Store() can be called concurrently; in
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// this case, do `dst.Store(src.Load())` instead.
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//
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// +stateify savable
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type AtomicPtr struct {
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ptr unsafe.Pointer `state:".(*Value)"`
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}
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func (p *AtomicPtr) savePtr() *Value {
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return p.Load()
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}
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func (p *AtomicPtr) loadPtr(v *Value) {
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p.Store(v)
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}
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// Load returns the value set by the most recent Store. It returns nil if there
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// has been no previous call to Store.
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//
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//go:nosplit
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func (p *AtomicPtr) Load() *Value {
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return (*Value)(atomic.LoadPointer(&p.ptr))
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}
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// Store sets the value returned by Load to x.
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func (p *AtomicPtr) Store(x *Value) {
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atomic.StorePointer(&p.ptr, (unsafe.Pointer)(x))
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}
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// Swap atomically stores `x` into *p and returns the previous *p value.
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func (p *AtomicPtr) Swap(x *Value) *Value {
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return (*Value)(atomic.SwapPointer(&p.ptr, (unsafe.Pointer)(x)))
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}
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