mpagealloc_32bit.go

     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 386 || arm || mips || mipsle || wasm
     6  
     7  // wasm is a treated as a 32-bit architecture for the purposes of the page
     8  // allocator, even though it has 64-bit pointers. This is because any wasm
     9  // pointer always has its top 32 bits as zero, so the effective heap address
    10  // space is only 2^32 bytes in size (see heapAddrBits).
    11  
    12  package runtime
    13  
    14  import "unsafe"
    15  
    16  const (
    17  	// The number of levels in the radix tree.
    18  	summaryLevels = 4
    19  
    20  	// Constants for testing.
    21  	pageAlloc32Bit = 1
    22  	pageAlloc64Bit = 0
    23  
    24  	// Number of bits needed to represent all indices into the L1 of the
    25  	// chunks map.
    26  	//
    27  	// See (*pageAlloc).chunks for more details. Update the documentation
    28  	// there should this number change.
    29  	pallocChunksL1Bits = 0
    30  )
    31  
    32  // See comment in mpagealloc_64bit.go.
    33  var levelBits = [summaryLevels]uint{
    34  	summaryL0Bits,
    35  	summaryLevelBits,
    36  	summaryLevelBits,
    37  	summaryLevelBits,
    38  }
    39  
    40  // See comment in mpagealloc_64bit.go.
    41  var levelShift = [summaryLevels]uint{
    42  	heapAddrBits - summaryL0Bits,
    43  	heapAddrBits - summaryL0Bits - 1*summaryLevelBits,
    44  	heapAddrBits - summaryL0Bits - 2*summaryLevelBits,
    45  	heapAddrBits - summaryL0Bits - 3*summaryLevelBits,
    46  }
    47  
    48  // See comment in mpagealloc_64bit.go.
    49  var levelLogPages = [summaryLevels]uint{
    50  	logPallocChunkPages + 3*summaryLevelBits,
    51  	logPallocChunkPages + 2*summaryLevelBits,
    52  	logPallocChunkPages + 1*summaryLevelBits,
    53  	logPallocChunkPages,
    54  }
    55  
    56  // See mpagealloc_64bit.go for details.
    57  func (p *pageAlloc) sysInit() {
    58  	// Calculate how much memory all our entries will take up.
    59  	//
    60  	// This should be around 12 KiB or less.
    61  	totalSize := uintptr(0)
    62  	for l := 0; l < summaryLevels; l++ {
    63  		totalSize += (uintptr(1) << (heapAddrBits - levelShift[l])) * pallocSumBytes
    64  	}
    65  	totalSize = alignUp(totalSize, physPageSize)
    66  
    67  	// Reserve memory for all levels in one go. There shouldn't be much for 32-bit.
    68  	reservation := sysReserve(nil, totalSize)
    69  	if reservation == nil {
    70  		throw("failed to reserve page summary memory")
    71  	}
    72  	// There isn't much. Just map it and mark it as used immediately.
    73  	sysMap(reservation, totalSize, p.sysStat)
    74  	sysUsed(reservation, totalSize)
    75  
    76  	// Iterate over the reservation and cut it up into slices.
    77  	//
    78  	// Maintain i as the byte offset from reservation where
    79  	// the new slice should start.
    80  	for l, shift := range levelShift {
    81  		entries := 1 << (heapAddrBits - shift)
    82  
    83  		// Put this reservation into a slice.
    84  		sl := notInHeapSlice{(*notInHeap)(reservation), 0, entries}
    85  		p.summary[l] = *(*[]pallocSum)(unsafe.Pointer(&sl))
    86  
    87  		reservation = add(reservation, uintptr(entries)*pallocSumBytes)
    88  	}
    89  }
    90  
    91  // See mpagealloc_64bit.go for details.
    92  func (p *pageAlloc) sysGrow(base, limit uintptr) {
    93  	if base%pallocChunkBytes != 0 || limit%pallocChunkBytes != 0 {
    94  		print("runtime: base = ", hex(base), ", limit = ", hex(limit), "\n")
    95  		throw("sysGrow bounds not aligned to pallocChunkBytes")
    96  	}
    97  
    98  	// Walk up the tree and update the summary slices.
    99  	for l := len(p.summary) - 1; l >= 0; l-- {
   100  		// Figure out what part of the summary array this new address space needs.
   101  		// Note that we need to align the ranges to the block width (1<<levelBits[l])
   102  		// at this level because the full block is needed to compute the summary for
   103  		// the next level.
   104  		lo, hi := addrsToSummaryRange(l, base, limit)
   105  		_, hi = blockAlignSummaryRange(l, lo, hi)
   106  		if hi > len(p.summary[l]) {
   107  			p.summary[l] = p.summary[l][:hi]
   108  		}
   109  	}
   110  }
   111
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