Re: [RFC PATCH v2 1/6] slub: Keep track of whether slub is on the per-node partial list

[Matthew Wilcox]

On Sat, Oct 21, 2023 at 02:43:12PM +0000, chengming.zhou@xxxxxxxxx wrote:
> +++ b/include/linux/page-flags.h
> @@ -478,6 +478,8 @@ PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
>  	TESTCLEARFLAG(Active, active, PF_HEAD)
>  PAGEFLAG(Workingset, workingset, PF_HEAD)
>  	TESTCLEARFLAG(Workingset, workingset, PF_HEAD)
> +	__SETPAGEFLAG(Workingset, workingset, PF_HEAD)
> +	__CLEARPAGEFLAG(Workingset, workingset, PF_HEAD)

This makes me nervous.  The __ versions can only be used when there are
guaranteed to be no other accesses to the flags.  It's never going to
be the case that we want code to call __folio_set_workingset().

_Assuming_ that it's safe to use the non-atomic flag setting, I'd
rather see this done as ...

static inline void slab_set_node_partial(struct slab *slab)
{
	__folio_set_workingset(slab_folio(slab));
	__set_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
}