On Tue, Sep 10, 2019 at 10:41:31AM +0900, Tetsuo Handa wrote: > Yu Zhao wrote: > > I think we can safely assume PAGE_SIZE is unsigned long aligned and > > page->objects is non-zero. But if you don't feel comfortable with these > > assumptions, I'd be happy to ensure them explicitly. > > I know PAGE_SIZE is unsigned long aligned. If someone by chance happens to > change from "dynamic allocation" to "on stack", get_order() will no longer > be called and the bug will show up. > > I don't know whether __get_free_page(GFP_ATOMIC) can temporarily consume more > than 4096 bytes, but if it can, we might want to avoid "dynamic allocation". With GFP_ATOMIC and ~~__GFP_HIGHMEM, it shouldn't. > By the way, if "struct kmem_cache_node" is object which won't have many thousands > of instances, can't we embed that buffer into "struct kmem_cache_node" because > max size of that buffer is only 4096 bytes? It seems to me allocation in error path is better than always keeping a page around. But the latter may still be acceptable given it's done only when debug is on and, of course, on a per-node scale.
