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Date:   Tue, 12 Apr 2022 09:06:16 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Yu Zhao <yuzhao@google.com>, Stephen Rothwell <sfr@rothwell.id.au>,
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Subject: Re: [PATCH v10 05/14] mm: multi-gen LRU: groundwork
Message-ID: <20220412070616.GT2731@worktop.programming.kicks-ass.net>
References: <20220407031525.2368067-1-yuzhao@google.com>
 <20220407031525.2368067-6-yuzhao@google.com>
 <20220411191615.a34959bdcc25ef3f9c16a7ce@linux-foundation.org>
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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))