Re: [PATCH v10 05/14] mm: multi-gen LRU: groundwork

[Peter Zijlstra]

On Mon, Apr 11, 2022 at 07:16:15PM -0700, Andrew Morton wrote:

> > +{
> > +	int gen;
> > +	unsigned long old_flags, new_flags;
> > +
> > +	do {
> > +		new_flags = old_flags = READ_ONCE(folio->flags);
> > +		if (!(new_flags & LRU_GEN_MASK))
> > +			return false;
> > +
> > +		VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
> > +		VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio);
> > +
> > +		gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
> > +
> > +		new_flags &= ~LRU_GEN_MASK;
> > +		/* for shrink_page_list() */
> > +		if (reclaiming)
> > +			new_flags &= ~(BIT(PG_referenced) | BIT(PG_reclaim));
> > +		else if (lru_gen_is_active(lruvec, gen))
> > +			new_flags |= BIT(PG_active);
> > +	} while (cmpxchg(&folio->flags, old_flags, new_flags) != old_flags);

Also; please use the form:

	unsigned long new, old = READ_ONCE(folio->flags);

	do {
		new = /* something */ old;
	} while (!try_cmpxchg(&folio->flags, &old, new))