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std.heap.GeneralPurposeAllocator: fix large alloc accounting

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when mremap relocates an allocation
This commit is contained in:
Andrew Kelley 2025-02-03 21:38:08 -08:00
parent becd16859d
commit 601f632c27
1 changed files with 29 additions and 4 deletions
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33
lib/std/heap/general_purpose_allocator.zig
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@ -608,7 +608,7 @@ pub fn GeneralPurposeAllocator(comptime config: Config) type {
if (config.safety and old_mem.len != entry.value_ptr.bytes.len) {
var addresses: [stack_n]usize = [1]usize{0} ** stack_n;
var free_stack_trace = StackTrace{
var free_stack_trace: StackTrace = .{
.instruction_addresses = &addresses,
.index = 0,
};
@ -635,9 +635,15 @@ pub fn GeneralPurposeAllocator(comptime config: Config) type {
self.total_requested_bytes = new_req_bytes;
}
const opt_resized_ptr = if (may_move)
self.backing_allocator.rawRemap(old_mem, alignment, new_size, ret_addr)
else if (self.backing_allocator.rawResize(old_mem, alignment, new_size, ret_addr))
const opt_resized_ptr = if (may_move) b: {
// So that if the allocation moves, we can memcpy the
// `LargeAlloc` value directly from old to new location.
// It's also not clear to me whether removing one item from std
// lib hash map guarantees that unused capacity increases by
// one.
self.large_allocations.ensureUnusedCapacity(self.backing_allocator, 1) catch return null;
break :b self.backing_allocator.rawRemap(old_mem, alignment, new_size, ret_addr);
} else if (self.backing_allocator.rawResize(old_mem, alignment, new_size, ret_addr))
old_mem.ptr
else
null;
@ -660,6 +666,25 @@ pub fn GeneralPurposeAllocator(comptime config: Config) type {
}
entry.value_ptr.bytes = resized_ptr[0..new_size];
entry.value_ptr.captureStackTrace(ret_addr, .alloc);
// Update the key of the hash map if the memory was relocated.
if (resized_ptr != old_mem.ptr) {
const gop = self.large_allocations.getOrPutAssumeCapacity(@intFromPtr(resized_ptr));
if (config.retain_metadata and !config.never_unmap) {
// Backing allocator may be reusing memory that we're retaining metadata for
assert(!gop.found_existing or gop.value_ptr.freed);
} else {
assert(!gop.found_existing); // This would mean the kernel double-mapped pages.
}
gop.value_ptr.* = entry.value_ptr.*;
if (!config.retain_metadata) {
self.large_allocations.removeByPtr(entry.key_ptr);
} else {
entry.value_ptr.freed = true;
entry.value_ptr.captureStackTrace(ret_addr, .free);
}
}
return resized_ptr;
}