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std.heap.SmpAllocator: alternate freelist accounting

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Freelist length accounting in alloc had a negative impact, especially
with the integer type bumped up to u16, so I changed the system to be
based on counting slabs rather than total allocations.
This commit is contained in:
Andrew Kelley 2025-02-08 16:20:51 -08:00
parent bb5a4036e8
commit b09e3efad4
1 changed files with 5 additions and 6 deletions
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11
lib/std/heap/SmpAllocator.zig
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@ -51,9 +51,9 @@ const slab_len: usize = @max(std.heap.page_size_max, 64 * 1024);
/// Because of storing free list pointers, the minimum size class is 3.
const min_class = math.log2(@sizeOf(usize));
const size_class_count = math.log2(slab_len) - min_class;
/// When a freelist length exceeds this number, a `free` will rotate up to
/// `max_free_search` times before pushing.
const max_freelist_len: u8 = 255;
/// When a freelist length exceeds this number of slabs, a `free` will rotate
/// up to `max_free_search` times before pushing.
const max_freelist_len = 255;
const max_free_search = 1;
/// Before mapping a fresh page, `alloc` will rotate this many times.
const max_alloc_search = 1;
@ -142,7 +142,6 @@ fn alloc(context: *anyopaque, len: usize, alignment: mem.Alignment, ra: usize) ?
defer t.unlock();
const node: *usize = @ptrFromInt(top_free_ptr);
t.frees[class] = node.*;
t.freelist_lens[class] -|= 1;
return @ptrFromInt(top_free_ptr);
}
@ -223,7 +222,7 @@ fn free(context: *anyopaque, memory: []u8, alignment: mem.Alignment, ra: usize)
if (freelist_len < max_freelist_len) {
@branchHint(.likely);
defer t.unlock();
t.freelist_lens[class] = freelist_len +| 1;
t.freelist_lens[class] = freelist_len +| @intFromBool((@intFromPtr(node) % slab_len) == 0);
node.* = t.frees[class];
t.frees[class] = @intFromPtr(node);
return;
@ -231,7 +230,7 @@ fn free(context: *anyopaque, memory: []u8, alignment: mem.Alignment, ra: usize)
if (search_count >= max_free_search) {
defer t.unlock();
t.freelist_lens[class] = freelist_len +| 1;
t.freelist_lens[class] = freelist_len +| @intFromBool((@intFromPtr(node) % slab_len) == 0);
node.* = t.frees[class];
t.frees[class] = @intFromPtr(node);
return;