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fix DirectAllocator not unmapping unused pages on large alignments 

Fixes #2306
master
Ryan Liptak 2019-04-19 17:27:20 -07:00 committed by Andrew Kelley
parent d44d2784e6
commit 1030cc97ca
1 changed files with 15 additions and 14 deletions
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29
std/heap.zig
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@ -68,21 +68,22 @@ pub const DirectAllocator = struct {
if (addr == p.MAP_FAILED) return error.OutOfMemory;
if (alloc_size == n) return @intToPtr([*]u8, addr)[0..n];
const aligned_addr = (addr & ~usize(alignment - 1)) + alignment;
const aligned_addr = mem.alignForward(addr, alignment);
// We can unmap the unused portions of our mmap, but we must only
// pass munmap bytes that exist outside our allocated pages or it
// will happily eat us too.
// Since alignment > page_size, we are by definition on a page boundary.
const unused_start = addr;
const unused_len = aligned_addr - 1 - unused_start;
const err = p.munmap(unused_start, unused_len);
assert(p.getErrno(err) == 0);
// It is impossible that there is an unoccupied page at the top of our
// mmap.
// Unmap the extra bytes that were only requested in order to guarantee
// that the range of memory we were provided had a proper alignment in
// it somewhere. The extra bytes could be at the beginning, or end, or both.
const unused_start_len = aligned_addr - addr;
if (unused_start_len != 0) {
const err = p.munmap(addr, unused_start_len);
assert(p.getErrno(err) == 0);
}
const aligned_end_addr = std.mem.alignForward(aligned_addr + n, os.page_size);
const unused_end_len = addr + alloc_size - aligned_end_addr;
if (unused_end_len != 0) {
const err = p.munmap(aligned_end_addr, unused_end_len);
assert(p.getErrno(err) == 0);
}
return @intToPtr([*]u8, aligned_addr)[0..n];
},