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Source file src/runtime/mpagealloc_64bit.go

Documentation: runtime

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build amd64 || (!ios && arm64) || mips64 || mips64le || ppc64 || ppc64le || riscv64 || s390x
     6  // +build amd64 !ios,arm64 mips64 mips64le ppc64 ppc64le riscv64 s390x
     7  
     8  // See mpagealloc_32bit.go for why ios/arm64 is excluded here.
     9  
    10  package runtime
    11  
    12  import "unsafe"
    13  
    14  const (
    15  	// The number of levels in the radix tree.
    16  	summaryLevels = 5
    17  
    18  	// Constants for testing.
    19  	pageAlloc32Bit = 0
    20  	pageAlloc64Bit = 1
    21  
    22  	// Number of bits needed to represent all indices into the L1 of the
    23  	// chunks map.
    24  	//
    25  	// See (*pageAlloc).chunks for more details. Update the documentation
    26  	// there should this number change.
    27  	pallocChunksL1Bits = 13
    28  )
    29  
    30  // levelBits is the number of bits in the radix for a given level in the super summary
    31  // structure.
    32  //
    33  // The sum of all the entries of levelBits should equal heapAddrBits.
    34  var levelBits = [summaryLevels]uint{
    35  	summaryL0Bits,
    36  	summaryLevelBits,
    37  	summaryLevelBits,
    38  	summaryLevelBits,
    39  	summaryLevelBits,
    40  }
    41  
    42  // levelShift is the number of bits to shift to acquire the radix for a given level
    43  // in the super summary structure.
    44  //
    45  // With levelShift, one can compute the index of the summary at level l related to a
    46  // pointer p by doing:
    47  //   p >> levelShift[l]
    48  var levelShift = [summaryLevels]uint{
    49  	heapAddrBits - summaryL0Bits,
    50  	heapAddrBits - summaryL0Bits - 1*summaryLevelBits,
    51  	heapAddrBits - summaryL0Bits - 2*summaryLevelBits,
    52  	heapAddrBits - summaryL0Bits - 3*summaryLevelBits,
    53  	heapAddrBits - summaryL0Bits - 4*summaryLevelBits,
    54  }
    55  
    56  // levelLogPages is log2 the maximum number of runtime pages in the address space
    57  // a summary in the given level represents.
    58  //
    59  // The leaf level always represents exactly log2 of 1 chunk's worth of pages.
    60  var levelLogPages = [summaryLevels]uint{
    61  	logPallocChunkPages + 4*summaryLevelBits,
    62  	logPallocChunkPages + 3*summaryLevelBits,
    63  	logPallocChunkPages + 2*summaryLevelBits,
    64  	logPallocChunkPages + 1*summaryLevelBits,
    65  	logPallocChunkPages,
    66  }
    67  
    68  // sysInit performs architecture-dependent initialization of fields
    69  // in pageAlloc. pageAlloc should be uninitialized except for sysStat
    70  // if any runtime statistic should be updated.
    71  func (p *pageAlloc) sysInit() {
    72  	// Reserve memory for each level. This will get mapped in
    73  	// as R/W by setArenas.
    74  	for l, shift := range levelShift {
    75  		entries := 1 << (heapAddrBits - shift)
    76  
    77  		// Reserve b bytes of memory anywhere in the address space.
    78  		b := alignUp(uintptr(entries)*pallocSumBytes, physPageSize)
    79  		r := sysReserve(nil, b)
    80  		if r == nil {
    81  			throw("failed to reserve page summary memory")
    82  		}
    83  
    84  		// Put this reservation into a slice.
    85  		sl := notInHeapSlice{(*notInHeap)(r), 0, entries}
    86  		p.summary[l] = *(*[]pallocSum)(unsafe.Pointer(&sl))
    87  	}
    88  }
    89  
    90  // sysGrow performs architecture-dependent operations on heap
    91  // growth for the page allocator, such as mapping in new memory
    92  // for summaries. It also updates the length of the slices in
    93  // [.summary.
    94  //
    95  // base is the base of the newly-added heap memory and limit is
    96  // the first address past the end of the newly-added heap memory.
    97  // Both must be aligned to pallocChunkBytes.
    98  //
    99  // The caller must update p.start and p.end after calling sysGrow.
   100  func (p *pageAlloc) sysGrow(base, limit uintptr) {
   101  	if base%pallocChunkBytes != 0 || limit%pallocChunkBytes != 0 {
   102  		print("runtime: base = ", hex(base), ", limit = ", hex(limit), "\n")
   103  		throw("sysGrow bounds not aligned to pallocChunkBytes")
   104  	}
   105  
   106  	// addrRangeToSummaryRange converts a range of addresses into a range
   107  	// of summary indices which must be mapped to support those addresses
   108  	// in the summary range.
   109  	addrRangeToSummaryRange := func(level int, r addrRange) (int, int) {
   110  		sumIdxBase, sumIdxLimit := addrsToSummaryRange(level, r.base.addr(), r.limit.addr())
   111  		return blockAlignSummaryRange(level, sumIdxBase, sumIdxLimit)
   112  	}
   113  
   114  	// summaryRangeToSumAddrRange converts a range of indices in any
   115  	// level of p.summary into page-aligned addresses which cover that
   116  	// range of indices.
   117  	summaryRangeToSumAddrRange := func(level, sumIdxBase, sumIdxLimit int) addrRange {
   118  		baseOffset := alignDown(uintptr(sumIdxBase)*pallocSumBytes, physPageSize)
   119  		limitOffset := alignUp(uintptr(sumIdxLimit)*pallocSumBytes, physPageSize)
   120  		base := unsafe.Pointer(&p.summary[level][0])
   121  		return addrRange{
   122  			offAddr{uintptr(add(base, baseOffset))},
   123  			offAddr{uintptr(add(base, limitOffset))},
   124  		}
   125  	}
   126  
   127  	// addrRangeToSumAddrRange is a convienience function that converts
   128  	// an address range r to the address range of the given summary level
   129  	// that stores the summaries for r.
   130  	addrRangeToSumAddrRange := func(level int, r addrRange) addrRange {
   131  		sumIdxBase, sumIdxLimit := addrRangeToSummaryRange(level, r)
   132  		return summaryRangeToSumAddrRange(level, sumIdxBase, sumIdxLimit)
   133  	}
   134  
   135  	// Find the first inUse index which is strictly greater than base.
   136  	//
   137  	// Because this function will never be asked remap the same memory
   138  	// twice, this index is effectively the index at which we would insert
   139  	// this new growth, and base will never overlap/be contained within
   140  	// any existing range.
   141  	//
   142  	// This will be used to look at what memory in the summary array is already
   143  	// mapped before and after this new range.
   144  	inUseIndex := p.inUse.findSucc(base)
   145  
   146  	// Walk up the radix tree and map summaries in as needed.
   147  	for l := range p.summary {
   148  		// Figure out what part of the summary array this new address space needs.
   149  		needIdxBase, needIdxLimit := addrRangeToSummaryRange(l, makeAddrRange(base, limit))
   150  
   151  		// Update the summary slices with a new upper-bound. This ensures
   152  		// we get tight bounds checks on at least the top bound.
   153  		//
   154  		// We must do this regardless of whether we map new memory.
   155  		if needIdxLimit > len(p.summary[l]) {
   156  			p.summary[l] = p.summary[l][:needIdxLimit]
   157  		}
   158  
   159  		// Compute the needed address range in the summary array for level l.
   160  		need := summaryRangeToSumAddrRange(l, needIdxBase, needIdxLimit)
   161  
   162  		// Prune need down to what needs to be newly mapped. Some parts of it may
   163  		// already be mapped by what inUse describes due to page alignment requirements
   164  		// for mapping. prune's invariants are guaranteed by the fact that this
   165  		// function will never be asked to remap the same memory twice.
   166  		if inUseIndex > 0 {
   167  			need = need.subtract(addrRangeToSumAddrRange(l, p.inUse.ranges[inUseIndex-1]))
   168  		}
   169  		if inUseIndex < len(p.inUse.ranges) {
   170  			need = need.subtract(addrRangeToSumAddrRange(l, p.inUse.ranges[inUseIndex]))
   171  		}
   172  		// It's possible that after our pruning above, there's nothing new to map.
   173  		if need.size() == 0 {
   174  			continue
   175  		}
   176  
   177  		// Map and commit need.
   178  		sysMap(unsafe.Pointer(need.base.addr()), need.size(), p.sysStat)
   179  		sysUsed(unsafe.Pointer(need.base.addr()), need.size())
   180  	}
   181  }
   182  

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