Re: [PATCH 5/7] zsmalloc: embed struct zs_handle into zram and zswap entries

[Yosry Ahmed <yosry@kernel.org>]

> +#ifdef CONFIG_ZSMALLOC_REBIND_HANDLE
> +/**
> + * zs_rebind_handle() - Rebind an allocated object to a new handle.
> + * @pool: pool the object belongs to
> + * @dst: unallocated destination handle (must not be on the stack)
> + * @src: source handle that currently owns the object
> + *
> + * Rebinds the object from @src to @dst, updating the object header so
> + * compaction and page migration update @dst instead of @src, and resets
> + * @src.
> + */
> +void zs_rebind_handle(struct zs_pool *pool, struct zs_handle *dst,
> +		      struct zs_handle *src)
> +{
> +	struct size_class *class;
> +	struct zspage *zspage;
> +	unsigned long obj;
> +
> +	if (WARN_ON_ONCE(object_is_on_stack(dst) ||
> +			 zs_handle_is_allocated(dst) ||
> +			 !zs_handle_is_allocated(src)))
> +		return;
> +
> +	obj_class_get_and_lock(pool, src, &obj, &zspage, &class);
> +
> +	if (likely(!ZsHugePage(zspage))) {
> +		struct zpdesc *zpdesc;
> +		struct link_free *link;
> +		unsigned int obj_idx;
> +		unsigned long off;
> +		void *vaddr;

I think this would be easier to read if you move the declarations to the
top of the function, so that the different logic in the branches is more
obvious.

> +
> +		obj_to_location(obj, &zpdesc, &obj_idx);
> +		off = offset_in_page(class->size * obj_idx);
> +		vaddr = kmap_local_zpdesc(zpdesc);
> +		link = (struct link_free *)(vaddr + off);
> +		link->handle = (unsigned long)dst | OBJ_ALLOCATED_TAG;
> +		kunmap_local(vaddr);
> +	} else {
> +		zspage->first_zpdesc->handle =
> +			(unsigned long)dst | OBJ_ALLOCATED_TAG;
> +	}
> +
> +	record_obj(dst, obj);
> +	record_obj(src, 0);
> +	spin_unlock(&class->lock);
> +}
> +EXPORT_SYMBOL_GPL(zs_rebind_handle);
> +#endif