Commit b09e3efad444a0008f8a6cd858f9b4c45f23f743 | zig

author	Andrew Kelley <andrew@ziglang.org> 2025-02-08 16:20:51-08:00
committer	Andrew Kelley <andrew@ziglang.org> 2025-02-08 16:20:51-08:00
log	b09e3efad444a0008f8a6cd858f9b4c45f23f743
tree	ff628049f75ce8e52855cd299281b81aad3af1fd
parent	bb5a4036e82ef15ac73003124fbf1adf3455e6d7

std.heap.SmpAllocator: alternate freelist accounting

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.

1 files changed, 5 insertions(+), 6 deletions(-)

lib
- std
  - heap
    SmpAllocator.zig

lib/std/heap/SmpAllocator.zig+5-6

...	@@ -51,9 +51,9 @@ const slab_len: usize = @max(std.heap.page_size_max, 64 * 1024);	...	@@ -51,9 +51,9 @@ const slab_len: usize = @max(std.heap.page_size_max, 64 * 1024);
51	/// Because of storing free list pointers, the minimum size class is 3.	51	/// Because of storing free list pointers, the minimum size class is 3.
52	const min_class = math.log2(@sizeOf(usize));	52	const min_class = math.log2(@sizeOf(usize));
53	const size_class_count = math.log2(slab_len) - min_class;	53	const size_class_count = math.log2(slab_len) - min_class;
54	/// When a freelist length exceeds this number, a `free` will rotate up to	54	/// When a freelist length exceeds this number of slabs, a `free` will rotate
55	/// `max_free_search` times before pushing.	55	/// up to `max_free_search` times before pushing.
56	const max_freelist_len: u8 = 255;	56	const max_freelist_len = 255;
57	const max_free_search = 1;	57	const max_free_search = 1;
58	/// Before mapping a fresh page, `alloc` will rotate this many times.	58	/// Before mapping a fresh page, `alloc` will rotate this many times.
59	const max_alloc_search = 1;	59	const max_alloc_search = 1;
...	@@ -142,7 +142,6 @@ fn alloc(context: *anyopaque, len: usize, alignment: mem.Alignment, ra: usize) ?	...	@@ -142,7 +142,6 @@ fn alloc(context: *anyopaque, len: usize, alignment: mem.Alignment, ra: usize) ?
142	defer t.unlock();	142	defer t.unlock();
143	const node: *usize = @ptrFromInt(top_free_ptr);	143	const node: *usize = @ptrFromInt(top_free_ptr);
144	t.frees[class] = node.*;	144	t.frees[class] = node.*;
145	t.freelist_lens[class] -\|= 1;
146	return @ptrFromInt(top_free_ptr);	145	return @ptrFromInt(top_free_ptr);
147	}	146	}
148		147
...	@@ -223,7 +222,7 @@ fn free(context: *anyopaque, memory: []u8, alignment: mem.Alignment, ra: usize)	...	@@ -223,7 +222,7 @@ fn free(context: *anyopaque, memory: []u8, alignment: mem.Alignment, ra: usize)
223	if (freelist_len < max_freelist_len) {	222	if (freelist_len < max_freelist_len) {
224	@branchHint(.likely);	223	@branchHint(.likely);
225	defer t.unlock();	224	defer t.unlock();
226	t.freelist_lens[class] = freelist_len +\| 1;	225	t.freelist_lens[class] = freelist_len +\| @intFromBool((@intFromPtr(node) % slab_len) == 0);
227	node.* = t.frees[class];	226	node.* = t.frees[class];
228	t.frees[class] = @intFromPtr(node);	227	t.frees[class] = @intFromPtr(node);
229	return;	228	return;
...	@@ -231,7 +230,7 @@ fn free(context: *anyopaque, memory: []u8, alignment: mem.Alignment, ra: usize)	...	@@ -231,7 +230,7 @@ fn free(context: *anyopaque, memory: []u8, alignment: mem.Alignment, ra: usize)
231		230
232	if (search_count >= max_free_search) {	231	if (search_count >= max_free_search) {
233	defer t.unlock();	232	defer t.unlock();
234	t.freelist_lens[class] = freelist_len +\| 1;	233	t.freelist_lens[class] = freelist_len +\| @intFromBool((@intFromPtr(node) % slab_len) == 0);
235	node.* = t.frees[class];	234	node.* = t.frees[class];
236	t.frees[class] = @intFromPtr(node);	235	t.frees[class] = @intFromPtr(node);
237	return;	236	return;