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std.heap.PageAllocator: align hint

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rpkak 2026-02-01 11:21:16 +01:00 • committed by Andrew Kelley
parent e9b442db5a
commit 184c8f9545
1 changed files with 9 additions and 7 deletions
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16
lib/std/heap/PageAllocator.zig
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@ -87,12 +87,14 @@ pub fn map(n: usize, alignment: mem.Alignment) ?[*]u8 {
}
const aligned_len = mem.alignForward(usize, n, page_size);
const max_drop_len = alignment_bytes - @min(alignment_bytes, page_size);
const overalloc_len = if (max_drop_len <= aligned_len - n)
aligned_len
else
mem.alignForward(usize, aligned_len + max_drop_len, page_size);
const hint = @atomicLoad(@TypeOf(std.heap.next_mmap_addr_hint), &std.heap.next_mmap_addr_hint, .unordered);
const max_drop_len = alignment_bytes -| page_size;
const overalloc_len = aligned_len + max_drop_len;
const maybe_unaligned_hint = @atomicLoad(@TypeOf(std.heap.next_mmap_addr_hint), &std.heap.next_mmap_addr_hint, .unordered);
// Aligning hint does not use mem.alignPointer, because it is slow.
// Aligning hint does not use mem.alignForward, because it asserts that there will be no overflow.
const hint: ?[*]align(page_size_min) u8 = @ptrFromInt(((@intFromPtr(maybe_unaligned_hint)) +% (alignment_bytes - 1)) & ~(alignment_bytes - 1));
const slice = posix.mmap(
hint,
overalloc_len,
@ -110,7 +112,7 @@ pub fn map(n: usize, alignment: mem.Alignment) ?[*]u8 {
const remaining_len = overalloc_len - drop_len;
if (remaining_len > aligned_len) posix.munmap(@alignCast(result_ptr[aligned_len..remaining_len]));
const new_hint: [*]align(page_size_min) u8 = @alignCast(result_ptr + aligned_len);
_ = @cmpxchgStrong(@TypeOf(std.heap.next_mmap_addr_hint), &std.heap.next_mmap_addr_hint, hint, new_hint, .monotonic, .monotonic);
_ = @cmpxchgStrong(@TypeOf(std.heap.next_mmap_addr_hint), &std.heap.next_mmap_addr_hint, maybe_unaligned_hint, new_hint, .monotonic, .monotonic);
return result_ptr;
}