bcachefs: Use mmap() instead of vmalloc_exec() in userspace

Calling mmap() directly is much better than malloc() then mprotect(), we
end up with much less address space fragmentation.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_cache.c

@@ -33,21 +33,21 @@ static inline unsigned btree_cache_can_free(struct btree_cache *bc)
 	return max_t(int, 0, bc->used - bc->reserve);
 }
 
-static void __btree_node_data_free(struct bch_fs *c, struct btree *b)
+static void btree_node_data_free(struct bch_fs *c, struct btree *b)
 {
+	struct btree_cache *bc = &c->btree_cache;
+
 	EBUG_ON(btree_node_write_in_flight(b));
 
 	kvpfree(b->data, btree_bytes(c));
 	b->data = NULL;
+#ifdef __KERNEL__
 	kvfree(b->aux_data);
+#else
+	munmap(b->aux_data, btree_aux_data_bytes(b));
+#endif
 	b->aux_data = NULL;
-}
 
-static void btree_node_data_free(struct bch_fs *c, struct btree *b)
-{
-	struct btree_cache *bc = &c->btree_cache;
-
-	__btree_node_data_free(c, b);
 	bc->used--;
 	list_move(&b->list, &bc->freed);
 }
@@ -75,8 +75,15 @@ static int btree_node_data_alloc(struct bch_fs *c, struct btree *b, gfp_t gfp)
 	b->data = kvpmalloc(btree_bytes(c), gfp);
 	if (!b->data)
 		return -ENOMEM;
-
+#ifdef __KERNEL__
 	b->aux_data = kvmalloc(btree_aux_data_bytes(b), gfp);
+#else
+	b->aux_data = mmap(NULL, btree_aux_data_bytes(b),
+			   PROT_READ|PROT_WRITE|PROT_EXEC,
+			   MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
+	if (b->aux_data == MAP_FAILED)
+		b->aux_data = NULL;
+#endif
 	if (!b->aux_data) {
 		kvpfree(b->data, btree_bytes(c));
 		b->data = NULL;