Re: [PATCH] zsmalloc: fix a race with deferred_handles storing

Sergey Senozhatsky
2023-02-01T01:16:15Z

On (23/01/10 15:17), Nhat Pham wrote:
> +#ifdef CONFIG_ZPOOL
> +/*
> + * The second least-significant bit in the object's header identifies if the
> + * value stored at the header is a deferred handle from the last reclaim
> + * attempt.
> + *
> + * As noted above, this is valid because we have room for two bits.
> + */
> +#define OBJ_DEFERRED_HANDLE_TAG 2
> +#define OBJ_TAG_BITS 2
> +#define OBJ_TAG_MASK (OBJ_ALLOCATED_TAG | OBJ_DEFERRED_HANDLE_TAG)
> +#else
> +#define OBJ_TAG_BITS 1
> +#define OBJ_TAG_MASK OBJ_ALLOCATED_TAG
> +#endif /* CONFIG_ZPOOL */
> +
> #define OBJ_INDEX_BITS (BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
> #define OBJ_INDEX_MASK ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
>
> @@ -222,6 +238,12 @@ struct link_free {
> * Handle of allocated object.
> */
> unsigned long handle;
> +#ifdef CONFIG_ZPOOL
> + /*
> + * Deferred handle of a reclaimed object.
> + */
> + unsigned long deferred_handle;
> +#endif

A nit:
Do we really need to have that #ifdef and add a member to anon uion?
I see that we use ->deferred_handle only in one place, so I'm not sure
if it makes code any simpler.