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

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Date:   Tue, 12 Apr 2022 09:06:16 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Yu Zhao <yuzhao@...gle.com>, Stephen Rothwell <sfr@...hwell.id.au>,
        linux-mm@...ck.org, Andi Kleen <ak@...ux.intel.com>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
        Barry Song <21cnbao@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, page-reclaim@...gle.com,
        x86@...nel.org, Brian Geffon <bgeffon@...gle.com>,
        Jan Alexander Steffens <heftig@...hlinux.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Steven Barrett <steven@...uorix.net>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Daniel Byrne <djbyrne@....edu>,
        Donald Carr <d@...os-reins.com>,
        Holger Hoffstätte 
        <holger@...lied-asynchrony.com>,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>,
        Shuang Zhai <szhai2@...rochester.edu>,
        Sofia Trinh <sofia.trinh@....works>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v10 05/14] mm: multi-gen LRU: groundwork

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))